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In this study, we propose an advanced tunnel oxide passivated contact (TOPCon) solar cell structure for bifacial usage. The proposed structure, named advanced industrial TOPCon (Ai-TOPCon), adopts rear-side local carrier-selective contacts to avoid rear-side light-absorption loss. Ai-TOPCon features larger rear-side light currents and improves the power density by approximately 0.28 mW/cm2 for bifacial usage in a 20% albedo scenario. Several types of Ai-TOPCon and industrial TOPCon (i-TOPCon) are evaluated, and the optimization of the structure resulted in a power density of 28.73 mW/cm2. Loss analysis revealed that the reduced Auger recombination volume was the main factor contributing to the improvement of cell performance, and the light-absorption problem was solved by reducing the rear-side heavy-doped region. [ABSTRACT FROM AUTHOR]

Ion-induced SETs were captured from a germanium photodiode (PD) in an integrated silicon photonics technology platform. Statistics from 400 ion-strike events were extracted for various optical powers and LETs incident on the PD. The results show that the transient peak decreases with increasing optical power. TCAD simulation results indicate that photo-generated carriers decrease the built-in electric field of the PD, thereby decreasing the transient peak. The photo-generated carriers also increase the probability of Auger recombination, which further reduces the transient peak under illuminated conditions, but this effect is small and does not contribute significantly to the transient peak reduction. Finally, a short case study with an ON–OFF keying modulation scheme is presented to show how these transients have the potential to corrupt bits in realistic communication systems. Furthermore, it is also shown that hardening techniques can be utilized to mitigate bit errors in communication systems that use integrated Ge PDs. [ABSTRACT FROM AUTHOR]

The intrinsic toxicity-free indium phosphide (InP) quantum dots (QDs) are regarded as the most promising alternative to the heavy metal-containing QDs for quantum dot light-emitting diodes (QLEDs) in next-generation display and lighting applications. Here, a stepwise hole injection layer consisting of PEDOT:PSS and solution-processed molybdenum oxide is employed to improve the hole injection for solution-processed green QLEDs based on InP/ZnSe/ZnS colloidal QDs. The hole transport layer (HTL) of poly(vinylcarbazole) with high-lying LUMO level is further used to block electrons. As a result, the electron-hole recombination zone is restricted in the middle of the InP/ZnSe/ZnS QDs emissive layer, reducing the possibility of exciton quenching at HTL and/or the HTL/QDs interface. This enables high-efficiency green InP-based QLEDs with the peak external quantum efficiency, current efficiency, and luminance of 5.84%, 20.8 cd/A, 5145 cd/m2, respectively. [ABSTRACT FROM AUTHOR]

The effect of Auger electron–hole asymmetry on the efficiency droop in indium gallium nitride quantum well (InGaN-QW) light-emitting diodes (LEDs) is investigated through a new open boundary quantum solver based on variational principles: Open Boundary Quantum LED Simulator (OBQ-LEDsim). OBQ-LEDsim eliminates the need for forcing artificial boundary conditions in LED simulations and features explicit expression of wavefunction with high generality, enabling incorporation of wavefunction penetration into barriers, quantum-confined Stark effects, and excitonic effects. As such, the Auger recombination’s primary channel is found to be the hhe Auger recombination because holes are more localized than electrons in the quantum well. Varying the ratio of electron ($\text{C}_{\mathrm {n}}$) to hole ($\text{C}_{\mathrm {p}}$), Auger coefficient $\text{C}_{\mathrm {n}}/\text{C}_{\mathrm {p}}$ , from 0 to $\infty $ suppresses the hhe Auger recombination, resulting in 25% higher electron and hole sheet charge densities in the LED active layer. This increases carrier screening of the polarization-induced electric fields and weakens quantum-confined Stark effects. One observes a 75% increase in the electron and hole square wavefunction overlap and an 8 nm blueshift in the peak emission wavelength. As a result, the efficiency droop in an InGaN-QW LED is reduced by a factor of 2 when the $\text{C}_{\mathrm {n}}/\text{C}_{\mathrm {p}}$ is increased from 0 to $\infty $ , whereas the ambipolar Auger coefficient is overestimated by as much as 62% if the Auger electron–hole asymmetry is neglected ($\text{C}_{\mathrm {n}}/\text{C}_{\mathrm {p}} \sim ~1$). [ABSTRACT FROM AUTHOR]

In this study, the Gadolinium metal based organic framework (Gd-MOF) is synthesized using the hydrothermal route. The as-synthesized material is dissolved in solvent and used to fabricate organic light emitting diodes (OLEDs) in the device structure ITO/PEDOT:PSS/poly-TPD/Gd-MOF/TPBi/LiF/Al. The luminance of Gd-MOF based OLED is found to be of 35.9 cd/m2 at 8 V. In the emission spectra, three peaks viz. blue, green and red are obtained at 425 nm, 480 nm and 600 nm respectively with excitation at 325 nm. By tuning the operating voltage, we have been able to achieve a white emission from our device in which the peak at 425 nm arises due to poly-TPD however the other two peaks at 480 nm and 600 nm come from Gd-MOF respectively. The voltage dependent study of the electroluminescence spectra of our device indicates that poly-TPD peak intensity increases significantly with the increase in voltage and exceeds the intensity of Gd-MOF peak (488 nm) after 7.5 V. It is also observed that the luminance intensities of Gd-MOF peaks tend to be saturated after 7 V. This is due to the fact that the electron-hole recombination region of our device expands with increasing operating voltage. At lower voltage, the radiative recombination zone is mainly confined within the Gd-MOF region however with increasing voltage the exciton accumulation gradually expands to the Poly-TPD region resulting in a gradual increase in the poly-TPD emission keeping the Gd-MOF emission as to be saturated.

The recombination rates in an In0.25Ga0.75N/Al0.48Ga0.52N/GaN multiple quantum well (MQW) structure are measured to identify the cause of low efficiencies in high In-content InGaN quantum wells. The MQWs emit from 640 to 565 nm and are grown using metal-organic chemical vapor deposition (MOCVD). The addition of AlGaN interlayers within the MQW provides strain balancing and suppresses defect formation in high In-content InGaN quantum wells. The rates are found by transforming the optically measured radiative efficiency, differential carrier lifetimes, and optical absorption. Both components of non-radiative recombination rates, Shockley-Read-Hall (SRH) and Auger recombination, are found to be similar to the values of blue-emitting InGaN MQWs. The low SRH recombination rate is attributed to the use of the AlGaN interlayer. The radiative recombination rate, however, is more than an order of magnitude lower compared to blue emitting (lower In-content) InGaN-based MQWs. While this large reduction in radiative rate can be attributed to differences in carrier overlap and transition energy, it may also include effects of variations in thickness and compositional inhomogeneities. [ABSTRACT FROM AUTHOR]

Mechanism of increase in the ON-state voltage of 4H-SiC PiN diodes due to the expansion of single-Shockley-stacking faults (1SSFs), so-called bipolar degradation, was investigated by performing a technology computer-aided design (TCAD) simulation. Electrical characteristics in 15-kV class PiN diodes with a 1SSF monolayer in a voltage-blocking layer were calculated while modeling the 1SSF as a quantum well (QW) for electron conduction. The simulation results clarified that a potential barrier formed by electrons trapped in the QW does not significantly deteriorate the current conduction under a low applied voltage due to hole current and recombination current paths. However, since the concentration of trapped carriers in the QW becomes extremely high especially when increasing the applied voltage, direct and Auger recombination occurs considerably around the 1SSF. This suppresses the conductivity modulation, and then the contribution of the hole current decreases, leading to significant disturbance of the current flow due to the potential barrier and large voltage drop at the 1SSF. Accordingly, the increase in the ON-state voltage of SiC bipolar devices is attributed to both electron trapping to the QW and enhanced carrier recombination around the 1SSF. [ABSTRACT FROM AUTHOR]

We determine the uncertainties on simulated efficiencies of silicon solar cells due to uncertainties of the fundamental physical models. To determine these, we refit their parameters to the underlying measurement data. Using a metamodeling and Monte Carlo simulation approach, we then deduce how these propagate to the simulated solar cell efficiency. This is evaluated for 150- $\mu \text{m}$ -thick 1 $\Omega $ cm p-type standard and advanced silicon passivated emitter and rear cells (PERC), as well as for an ideal silicon solar cell. When sticking to the best-known set of physical models, we determine resulting efficiency uncertainties as low as 0.06%abs for usual PERC cells and 0.1%abs for an ideal cell. In a variance-based sensitivity analysis, we find the uncertainties of the bandgap and the hole density-of-states effective mass as well as the Auger recombination in the limiting case to dominate the efficiency uncertainty. In addition to these relatively low uncertainties, larger discrepancies may arise when applying different physical models for otherwise fixed device properties. We determine comparably large efficiency discrepancies of up to 0.6%abs for the two most prominent bandgap narrowing (BGN) models, and up to 0.15%abs for the two most recent parameterizations of free carrier absorption. We also show evidence that for the specific case of a strong space charge region being present at a recombining surface, Schenk’s BGN model fails to replicate experiments. Those discrepancies highlight the necessity of further research on those models. Finally, an error of up to 0.08%abs is observed by simplifying diffused regions on textured surfaces to a planar geometry. [ABSTRACT FROM AUTHOR]

This paper investigates the influences of various topside cell structures of insulated gate bipolar transistor (IGBT) on the current crowding effect during high current turn-off by symmetricalmulticell numerical simulations. It is observed that lower breakdown electric field in the drift region can reduce the negative differential resistance in the forward blocking curve and therefore suppress the current crowding effect during high current turn-off. We refer to this characteristic as the self-suppressing current crowding effect (SSCCE). Different topside cell structures of IGBT have considerable influence on the SSCCE. Amodest increment of the SSCCE by proper topside structure design provides an alternative solution to improve the ruggedness of IGBT, especially for the strong punchthrough or low current gain IGBTs. [ABSTRACT FROM AUTHOR]

Safe-operating-area (SOA) in a high-voltage complementary silicon–germanium (SiGe) (= n-p-n + p-n-p) on silicon-on-insulator (SOI) technology is investigated from 24 °C to 300 °C. Three key reliability degradation regions are identified, including: 1) high-current; 2) mixed-mode; and 3) high-power. The degradation mechanisms, which are operative, including Auger damage, mixed-mode damage, and electrothermal runaway as well as their temperature dependences are identified. Mixed-mode damage exhibits a strong negative temperature coefficient for both n-p-n and p-n-p SiGe heterojunction bipolar transistors (HBTs) up to 300 °C, which leads to an increase in the SOA from a high-voltage perspective. Electrothermal boundaries are also explored by finding JC,{\textsf {crit}} and V{\textsf {CB},{\textsf {crit}}} across the JC – V\textsf {CB} plane up to 300 °C. Both n-p-n and p-n-p SiGe HBTs show an increase in the SOA for the electrothermal boundary as temperature increases. High-current-induced damage, on the other hand, exhibits a positive temperature coefficient, which implies that high current drive should carefully be considered when using SiGe HBT circuits operated in a high-temperature environment. However, at very high temperatures (>200°C), the high current damage processes show annealing properties, which implies that at sufficiently high temperatures, annealing can dominate over Auger damage and potentially extend the SOA of the technology. [ABSTRACT FROM PUBLISHER]

In addition to the traditional existed static model, the dynamic model is proposed to investigate the thickness (${d}$) dependence of tribo-dielectric layer (TDL) with the device performance in the triboelectric nanogenerators (Tengs) in this work. With the involvement of one material parameter, i.e., electron-hole recombination rate (${r}$) near the TDL in our developed dynamic model, the d dependence of TDL for the effective surface charge (${Q}_{s}$) and output current (${I}$) in the Tengs is derived. The maximum ${I}$ (${I}_{{\text {max}}}$) with the optimized TDL thickness (${d}_{{\text {max}}}$) is further obtained with the consideration of different r. It can be found that the larger value of ${r}$ in the material results in the smaller value of ${I}_{{\text {max}}}$ and the larger value of ${d}_{{\text {max}}}$. At the same time, the theoretical dynamic model is compared with the experimental data. With the designed spin coating speed and time for the TDL deposition, the Tengs with different ${d}$ is demonstrated and studied experimentally. The experimental data and the theoretical dynamic model agree very well with each other. [ABSTRACT FROM AUTHOR]

This paper presents a Q-band orthomode transducer (OMT) that has been designed according to the mechanical constraints of the platelet (multi-layer) manufacturing strategy. It is composed of a twofold symmetric coupling section with two electrically identical recombination networks. The two OMT outputs lay on the same plane to provide a suitable interface to the correlation unit. The two channels are equalized in both magnitude and phase according to the correlation polarimeter requirements. They also exhibit a very low cross-coupling (-50 dB) and good reflection levels (-28 dB) in the 21% bandwidth. [ABSTRACT FROM PUBLISHER]

The characteristics of InGaN-based blue light-emitting diodes (LEDs) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al molar fraction below the active region are analyzed numerically. The output power, internal quantum efficiency, electrostatic fields, energy band diagrams, carrier concentrations, radiative recombination, and electron leakage current are investigated. The results indicate that the LED with n-type AlGaN/GaN SL EBL of gradual Al molar fraction has smaller electrostatic fields and lower electron leakage in its active region than the LED with a rectangular p-AlGaN EBL or n-AlGaN EBL. These result in a markedly reduced efficiency droop. [ABSTRACT FROM PUBLISHER]

This paper presents theoretical and experimental results on the energy loss characteristics of reversely switched dynistor (RSD) under high-current conditions. Theoretical analysis was performed based on a 1-D modified model by taking account into the carrier-carrier scattering effect and auger recombination effect during the conducting process. The experimental results of energy losses in RSD at various amplitudes of high pulse current were accurately obtained using the direct current injection method. The typical experimental results show that a single RSD has a voltage drop of approximately 9 V with a pulse current of 150 kA, transferred charge of 26.5 C. The theoretical calculated voltage drop based on 1-D modified model is approximately 7.7 V under the same conditions. The theoretical results based on the 1-D modified model almost agree well with the experimental results. [ABSTRACT FROM AUTHOR]

We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 × 6 k ·p method and, considering carrier distribution, recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on AlaGa1-aN (barrier)/AlbGa1-bN (MLI)/AlcGa1-cN (well)/AldGa1-dN (barrier), where b d a c. A large bandgap AlbGa1 - bN mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection. [ABSTRACT FROM PUBLISHER]

This paper exhibits systematic results for lateral light emitting diodes (LEDs) with various conditions. The simulation results and circuit model are both included to describe the current spreading effect at the same time. A fully 2-D model that solves Poisson and drift-diffusion equations to investigate the current flow and radiative recombination distribution specifies the uniformity of the carrier distribution, which is combined with the Monte Carlo ray tracing technique to calculate the light extraction efficiency (LEE). This paper focuses on the modulation of the transparent conducting layer. In addition, this paper will discuss bottom emission LEDs addressing the current spreading effect and LEE compared with top emission LEDs. We also examine the droop effect to verify our discussion. A thorough analysis provides deep insights for achieving high efficiency lateral LEDs. [ABSTRACT FROM PUBLISHER]

We deposited a p-i-n structure device with alternative amorphous Si (a-Si) and amorphous SiC (a-SiC) multilayers as an intrinsic layer in a plasma-enhanced chemical vapor deposition (PECVD) system. A KrF pulsed excimer laser-induced crystallization of a-Si/a-SiC stacked structures was used to prepare Si quantum dots (Si QDs)/SiC multilayers. The formation of Si QDs with an average size of 4 nm was confirmed by Raman spectra, whereas the layered structures were revealed by cross-sectional transmission electron microscopy. Electroluminescence (EL) devices containing Si QDs/SiC multilayers embedded in a p-n junction were fabricated, and the device performance was studied and compared with the reference device without the p-i-n structure. It was found that the turn-on voltage was reduced and that luminescence efficiency was significantly enhanced by using the p-i-n device structure. The recombination mechanism of carriers in a Si-QD-based EL device was also discussed, and the improved device performance can be attributed to the enhanced radiative recombination probability in a p-i-n EL device. [ABSTRACT FROM PUBLISHER]

The variations of the very low frequency noise (i.e., 100 mHz to 100 kHz) and the dc characteristics of unpassivated AlGaN/GaN modulation-doped field-effect transistors (MODFETs) with temperature from 300 to 500 K are investigated. The rise in temperature to 500 K is shown to reveal generation-recombination (G-R) noise characteristics within the 100 mHz to 1 Hz frequency range. It is experimentally evidenced that these manifestations can predict the existence of very slow transients in the drain-current characteristics of AlGaN/GaN MODFETs. Due to the very long time constant of the transients at room temperature (i.e., on the order of several hours or even days), the observed features can be classified as semipermanent. The comparison between the energy levels predicted by the noise data and the levels previously reported in literature supports these observations. [ABSTRACT FROM PUBLISHER]

In this paper, we report that low-density InAs/GaAs quantum dots (QDs) can be formed by postgrowth annealing the samples with 1.5-monolayer (ML) InAs coverage, which is thinner than the critical layer thickness for the Stranski-Krastanov growth. The annealing procedure was performed immediately after the deposition of the InAs layer. The effects of annealing time and annealing temperature on the dot density, dot size, and optical characteristics of the QDs were investigated. The optimum annealing conditions to obtain low-density QDs are longer than 60 s and higher than 500degC . Meanwhile, no luminescence can be observed for the wetting-layer, which may suggest that the postgrowth annealing will make the wetting layer thinner and thus reduce the effects of wetting layer on carrier relaxation and recombination. On the other hand, we observe that a decrease of the PL intensity at the annealing conditions of 60 s and 515degC , which is possibly due to the increasing surface dislocations resulted from the In adatom desorption at higher annealing temperature. [ABSTRACT FROM PUBLISHER]

Electrically driven thermal light emission (TLE) from individual metallic single-walled carbon nanotubes (mCNTs) is theoretically investigated by detailed simulations and compared to a recent experiment (Mann et al., Nature Nanotech.., vol. 2, p. 33, 2007). The electrical and thermal properties are determined by carrier transport in the metallic subband, which has a zero dipole matrix element and does not experience radiative carrier recombination. The light emission, however, is contributed by the semiconducting subbands, which are populated by a thermal process. The simulation results indicate that due to diameter-dependent thermal effects, the maximum current of suspended mCNTs has a much stronger dependence on the CNT diameter than in non suspended CNTs. The size and shape of the light spot are sensitive to the measured photon energy range. Although the temperature profile along the CNT is approximately parabolic, the light emission profile has a much sharper peak at the middle of the CNT, which is in good agreement with the experiment and confirms the thermal nature of the light emission. The light emission spectrum at high energies is affected by the subband and energy dependences of the radiative recombination lifetime. [ABSTRACT FROM PUBLISHER]

The role of changes in gain and nonradiative recombination as a function of temperature in p-doped quantum dot samples that exhibit a minimum in the threshold current versus temperature characteristics are examined using a detailed analysis based on the multisection measurement method. An injection level is defined as the difference between the transparency energy and the transition energy of the dot states so that the results at different temperatures may be compared. The temperature dependence of the injection level necessary to achieve the required gain produces the initial decrease in nonradiative recombination current and threshold current between 250-280 K. At higher temperatures, the nonradiative recombination increases due to both an increase in the injection level required to achieve a fixed value of gain and because of an increase in the nonradiative recombination at fixed injection level. Using measurements of the population inversion function it is shown that the reduction in the injection level required to achieve a fixed value of gain between 250-280 K is caused by the thermalization of the carrier distribution over this temperature range. Subsequent increases in the injection level required to achieve a fixed value of gain are due to the increasing thermal distribution of carriers over the available states at higher temperatures. [ABSTRACT FROM PUBLISHER]

We designed a silicon-processing compatible, simple, and cheap device operating at a power down to sub-muW. It has a pillar-shaped structure with a nanoscopic (10-100 nm in size) conductive link (the so-called antifuse) created between two electrodes separated by a SiO 2 layer. The device exhibits a diode-like behavior due to the depletion effects in the mono-silicon pillar. The device is capable of maintaining a microscopic hot-surface area of several hundreds degrees centigrade. The size of the hot area and its temperature can be manipulated by the sign of the applied bias. Two different heat-generation mechanisms (i.e., dissipation at a resistor and a non-radiative recombination of carriers) are proposed and modelled. Such a device can be used as a heat source, as a light source, and as a sensitive detector of light and heat. In this paper, we describe thermo-electrical properties of the fabricated devices and demonstrate their feasibility to perform as gas-, adsorption-, desorption sensors, and as units for activating chemisorption/decomposition of gaseous precursors, i.e., micro-reactors [ABSTRACT FROM PUBLISHER]

We analyze the temperature sensitivity of 1.5-μm GaInNAsSb lasers grown on GaAs. Building on the method of Tansu and coworkers, we find evidence that the characteristic temperatures for the threshold current T0 and external efficiency T1 are balanced by a combination of monomolecular recombination and temperature destabilizing mechanism(s) near room temperature. At elevated temperatures, the destabilizing process(es) dominate, due to increased threshold current density Jth. While it is difficult to definitively identify carrier leakage, Auger recombination, or a combination of the two as the responsible mechanism(s), results indicate that carrier leakage certainly plays a role. Evidence of intervalence band absorption was also found; T1 was reduced, but Jth and T0 were not significantly degraded. Conclusions are corroborated by supporting measurements of the Z-parameter with bias, spontaneous emission spectrum, and band-offsets. Spontaneous emission measurements show evidence of weak Fermi-level pinning within the active region at threshold, indicating a form of carrier leakage. This is consistent with the characteristic temperature analysis and a leakage mechanism is proposed. This process is partially responsible for the greater temperature sensitivity of device parameters and the poor internal efficiency. Methods for reducing the effects of each parasitic mechanism are also described. [ABSTRACT FROM PUBLISHER]

We show that even in quantum-dot (QD) lasers with very low threshold current densities (Jth=40--50 A/cm2 at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises ∼60% to 70% of Jth at 300 K, whereas the radiative part of Jth is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part of Jth, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-μm lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current. [ABSTRACT FROM PUBLISHER]

A simple and physical drain avalanche hot carrier lifetime model has been proposed. The model is based on a mechanism of interface trap generation caused by recombination of hot electrons and hot holes. The lifetime is modeled as τ(Id/W)2∝(Isub/Id)-m. The formula is different from the conventional τId/W-Isub/Id model in that the exponent of Id/W is 2, which results from the assumed mechanism of the two-carrier recombination. It is shown that the mechanism gives a physical basis of the empirical τ-Isub/W model for NMOSFETs. The proposed model has been validated experimentally both for NMOSFETs and for PMOSFETs. Model parameters extracted from experimental data show that carrier critical energies for creating damage are lower than the interface potential barriers. It is supposed that oxide band edge tailing enables low-energy carriers to create the damage. The channel hot electron condition becomes the worst case in short channel NMOSFETs, because gate voltage dependence of the maximum channel electric field decreases. [ABSTRACT FROM PUBLISHER]

We consider the combination of nonequilibrium Auger suppression with cavity enhancement, this being either resonant cavity enhancement (RCE) or photonic crystal enhancement (PCE) as a means to suppress generation-recombination processes in intrinsic semiconductor-based long wavelength infrared detectors. The aim is to approach the background-limited operation of narrow-bandgap compound semiconductor photodetectors in the 3-14 μm infrared wavelength range without cooling or possibly with slight cooling. Auger generation-recombination processes are suppressed utilizing exclusion, extraction, magnetoconcentration, or some of their combinations. The residual radiative recombination is removed by enclosing the detector active area into a cavity with a radiative shield (resonant cavity or photonic crystal) and using the benefits of reabsorption (photon recycling) to effectively increase radiative lifetime. [ABSTRACT FROM PUBLISHER]

InAs quantum-dot (QD) lasers were investigated in the temperature range 20-300 K and under hydrostatic pressure in the range of 0-12 kbar at room temperature. The results indicate that Auger recombination is very important in 1.3-μm QD lasers at room temperature and it is, therefore, the possible cause of the relatively low characteristic temperature observed, of T0=41K. In the 980-nm QD lasers where T0=110-130 K, radiative recombination dominates. The laser emission photon energy Elas increases linearly with pressure p at 10.1 and 8.3 meV/kbar for 980 nm and 1.3-μm QD lasers, respectively. For the 980-nm QD lasers the threshold current increases with pressure at a rate proportional to the square of the photon energy E2las. However, the threshold current of the 1.3-μm QD laser decreases by 26% over a 12-kbar pressure range. This demonstrates the presence of a nonradiative recombination contribution to the threshold current, which decreases with increasing pressure. The authors show that this nonradiative contribution is Auger recombination. The results are discussed in the framework of a theoretical model based on the electronic structure and radiative recombination calculations carried out using an 8×8 k·p Hamiltonian. [ABSTRACT FROM PUBLISHER]

We have investigated the temperature and pressure dependence of the threshold current (Ith) of 1.3 μm emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) and the equivalent edge-emitting laser (EEL) devices employing the same active region. Our measurements show that the VCSEL devices have the peak of the gain spectrum on the high-energy side of the cavity mode energy and hence operate over a wide temperature range. They show particularly promising Ith temperature insensitivity in the 250-350 K range. We have then used a theoretical model based on a 10-band k.P Hamiltonian and experimentally determined recombination coefficients from EELs to calculate the pressure and temperature dependency of Ith. The results show good agreement between the model and the experimental data, supporting both the validity of the model and the recombination rate parameters. We also show that for both device types, the super-exponential temperature dependency of Ith at 350 K and above is due largely to Auger recombination. [ABSTRACT FROM PUBLISHER]

The pressure dependence of the components of the recombination current at threshold in 1.3-μm GaInNAs single quantum-well lasers is presented using for the first time high-pressure spontaneous emission measurements up to 13 kbar. It is shown that, above 6 kbar, the rapid increase of the threshold current with increasing pressure is associated with the unusual increase of the Auger-related nonradiative recombination current, while the defect-related monomolecular nonradiative recombination current is almost constant. Theoretical calculations show that the increase of the Auger current can be attributed to a large increase in the threshold carrier density with pressure, which is mainly due to the increase in the electron effective mass arising from the enhanced level-anticrossing between the GaInNAs conduction band and the nitrogen level. [ABSTRACT FROM PUBLISHER]

A simple theory for the crosstalk in multichannel wavelength-division multiplexing (WDM) communication systems caused by the cross gain saturation in semiconductor optical amplifier (SOA) is developed. It is shown that increasing the carrier recombination lifetime while reducing the differential gain in the SOA greatly mitigates the crosstalk. An SOA using type-II quantum wells with reduced recombination probability is designed, and its characteristics are numerically modeled for a number of different WDM systems. It is shown that when used as a preamplifier or in local/metro networks with a small number of amplifiers, error-free transmission can be achieved with the type-II SOA. [ABSTRACT FROM PUBLISHER]

The temperature dependence of the characteristic temperature T0 of semiconductor quantum-well lasers is investigated using detailed simulations. The critical-temperature-dependent processes are the optical gain and the nonradiative recombination. The gain model is based on k · p theory with the multiple quantum wells in the active layer represented by a superlattice. The Auger process is assumed to be thermally activated. It is shown that, with inclusion of the continuum state filling and interband mixing, the most important features experimentally observed in the temperature dependence of the T0 value can be explained. The continuum state filling and band nonparabolicity cause a significant deviation from the ideal linear carrier density versus temperature relation for quantum wells. The results are compared to experiment for broad area devices lasing at 980 nm and 1.3, and 1.55 μm, and show good agreement over a broad range of temperature. [ABSTRACT FROM PUBLISHER]

Self-assembled GaN quantum dots (QDs), grown on AlN by molecular beam epitaxy, were investigated by time-resolved photoluminescence spectroscopy. We investigate the emission mechanism in GaN QDs by comparing the carrier recombination dynamics in single and multiple period QDs. At 100 K, the PL decay time in single period QD structures is considerably shorter than in stacked QDs. Compared to single period QDs, the room temperature PL efficiency is considerably enhanced in 20 period QDs due to the reduction in nonradiative recombination processes. [ABSTRACT FROM PUBLISHER]

By measuring the spontaneous emission (SE) from normally operating ∼1.3-μm GaInNAs-GaAs-based lasers we have quantitatively determined the variation of each of the current paths present in the devices as a function of temperature from 130 K to 370 K. From the SE measurements we determine how the current I close to threshold, varies as a function of carrier density n, which enables us to separate out the main current paths corresponding to monomolecular (defect-related), radiative or Auger recombination. We find that defect-related recombination forms ∼55% of the threshold current at room temperature (RT). At RT, radiative recombination accounts for ∼20% of Ith with the remaining ∼25% being due to nonradiative Auger recombination. Theoretical calculations of the threshold carrier, density as a function of temperature were also performed, using a ten-band k · p Hamiltonian. Together with the experimentally determined defect-related, radiative, and Auger currents we deduce the temperature variation of the respective recombination coefficients (A, B, and C). These are compared with theoretical calculations of the coefficients and good agreement is obtained. Our results suggest that by eliminating the dominant defect-related current path, the threshold current density of these GaInNAs-GaAs-based devices would be approximately halved at RT. Such devices could then have threshold current densities comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration. [ABSTRACT FROM PUBLISHER]

The report at the 1962 IRE Solid-State Device Research Conference (July, Durham, NH) of the generation and long-range transmission (and detection) of a recombination-radiation signal from a simple Zn-diffused GaAs p-n junction, a startling report, began the race to construct a semiconductor laser. The visible-spectrum II-V alloy GaAs1-xP x was in the middle of this activity and was (fall of 1962), with GaAs, a first semiconductor laser, not to mention the first laser in a semiconductor alloy or crystal that could be “tuned” in energy gap (and wavelength) from direct gap to indirect gap. The ternary GaAs1-xPx, the prototype of all present-day III-V alloys used in heterojunction and quantum-well devices, established uniquely the importance of a direct gap for a laser and inevitably for light emitting diodes (LEDs). The events leading to the GaAs1-x Px laser, as well as, in slightly different form, the first practical LED, are described. The significance of the work of 1962-1963 in launching the semiconductor laser is described, and the reasons why the semiconductor laser (an “ultimate lamp”) is predominant over all other forms of lasers [ABSTRACT FROM PUBLISHER]

This paper reports recent developments of our self-assembled InGaAs quantum-dot (QD) lasers and their unique physical properties. We achieved a low-threshold current of 5.4 mA at room temperature with our originally designed columnar-shaped QD's, and also, room-temperature 1.3-μm continuous-wave (CW) lasing with self-assembled dots grown at a decreased growth rate and covered by a strained InGaAs layer. We discuss influence of homogeneous broadening of single-dot optical gain on lasing spectra, influence of nonradiative carrier recombination on temperature characteristics of threshold currents, a model for the origin of the homogeneous broadening, a finding of random telegraph signals, and suppression of temperature sensitivity of interband emission energy by covering dots with a strained InGaAs layer [ABSTRACT FROM PUBLISHER]

In this letter, we propose a novel trench power MOSFET structure with a p-n junction in trench to reduce the gate charge. We utilize the 2-D device simulator, ATLAS, to investigate the characteristics of the proposed structure and compare with the conventional structure. As a result, the proposed structure exhibits 49.5% enhancement in gate-charge Q\mathrm {\mathbf {g}} as compared with the conventional structure, without degrading the other electrical characteristics. [ABSTRACT FROM PUBLISHER]

We investigate loss mechanisms in 1.55-μm InGaAsP-InP multiquantum-well ridge-waveguide laser diodes at room temperature. The common method of measuring light versus current curves and plotting the inverse slope efficiency versus laser length is employed to extract the internal optical loss αi and the differential internal efficiency η. This method neglects the dependence of both the parameters on the laser cavity length L. We analyze physical mechanisms behind these loss parameters and their length dependence using the commercial laser simulation software PICS3D. Internal optical losses are dominated by carrier density dependent absorption. The differential internal efficiency above threshold is found to be mainly restricted by carrier recombination losses within the quantum wells, i.e., Fermi level pinning is not observed. Both loss mechanisms are enhanced with shorter cavity length due to the higher quantum well carrier density. For the shortest device measured (L=269 μm), we extract αi=20 cm-1 and ηi=66%. With increasing cavity length, the loss parameters approach αi =15 cm-1 and ηi=70%. From the inverse slope efficiency versus cavity length plot, we obtain αi=14 cm-1 and ηi=67% independent of laser length [ABSTRACT FROM PUBLISHER]

We present a novel analysis for correcting the measured differential carrier lifetime to account for carrier population in both the barrier and separate confinement heterostructure (SCH) regions of quantum-well (QW) lasers. This analysis uses information obtained from the measured spontaneous emission spectra to correct the measured lifetime and obtain the intrinsic well lifetime. Once the intrinsic well lifetime is obtained, the intrinsic well recombination coefficients can also be obtained. We show that the carrier population in the barrier/SCH layers can significantly affect the measured carrier lifetime and the extracted recombination coefficients. We also show that this analysis yields transparency carrier density and differential gain numbers which are very different from those obtained with the traditional analysis and much closer to what is predicted for highly strained QW lasers. These differences indicate the importance of accounting for barrier/SCH carriers on the measurement of basic QW laser material properties [ABSTRACT FROM PUBLISHER]

We have studied experimentally and theoretically the spontaneous emission from 1.3- and 1.5-μm compressively strained InGaAsP multiple-quantum-well lasers in the temperature range 90-400 K to determine the variation of carrier density n with current I up to threshold. We find that the current contributing to spontaneous emission at threshold IRad is always well behaved and has a characteristic temperature T0 (IRad)≈T, as predicted by simple theory. This implies that the carrier density at threshold is also proportional to temperature. Below a breakpoint temperature TB, we find I α nZ, where Z=2. And the total current at threshold Ith also has a characteristic temperature T0 (Ith)≈T, showing that the current is dominated by radiative transitions right up to threshold. Above TB, Z increases steadily to Z≈3 and T0 (Ith) decreases to a value less than T/3. This behavior is explained in terms of the onset of Auger recombination above TB; a conclusion supported by measurements of the pressure dependence of Ith. From our results, we estimate that, at 300 K, Auger recombination accounts for 50% of Ith in the 1.3-μm laser and 80% of Ith in the 1.5-μm laser. Measurements of the spontaneous emission and differential efficiency indicate that a combination of increased optical losses and carrier overflow into the barrier and separate confinement heterostructure regions may further degrade T0 (Ith) above room temperature [ABSTRACT FROM PUBLISHER]

We have analyzed experimentally the temperature and pressure dependences of the lasing characteristics of 1.3-μm AlGaInAs-InP strained multiple-quantum-well lasers, by focusing on the ratio of the nonradiative recombination current to the total current. The temperature dependence of the radiative current was studied by observing the spontaneous emission through a window in the substrate. It was found to increase linearly with temperature, exactly as expected for an ideal quantum well over the entire temperature range from 100 to 360 K. Further, it was shown that pure radiative recombination dominated the total current below a breakpoint temperature Tb of 220 K. Above this temperature, the onset of loss processes including Auger recombination caused a superlinear increase in the threshold current. Analysis of the linear and nonlinear components allowed us to determine the ratio of the nonradiative to radiative currents at threshold. We find that, relative to similar GaInAsP/InP lasers, there is a decrease in the nonradiative component of the current, resulting in a higher characteristic temperature T0 in the AlGaInAs-InP lasers. At 300 K, the radiative recombination current is more than 70% of the total threshold current. This result is consistent with the observation that the threshold current increases by about 8% in 12-kbar hydrostatic pressure, while in GaInAsP lasers, a decrease of 10% or more is always observed over this pressure range [ABSTRACT FROM PUBLISHER]

In this letter, we develop a nearly white-light-emitting device by integrating blue/green emission from a GaN-based light-emitting diode with red emission from a porous SiO2 layer. The porous SiO 2 layer was fabricated by a novel process procedure to create Si nanocrystals on top of the n-type GaN layer. Red light is generated from the metal-oxide-semiconductor (Ni-Au-SiO2 oxide-n-type GaN) structure due to the electron-hole recombination in the Si nanocrystals. The device shows a blue light emission at a low biased voltage and nearly white-light emission (green and red colors) at a bias voltage between 14 and 16 V. Our results show the potential of applying such an integrated structure to white-light illumination [ABSTRACT FROM PUBLISHER]

An improved formulation of the frequency-dependent impedance for p-i-n diodes from physical and geometrical parameters is presented. This work is addressed to diode designers and allows them to evaluate quickly and accurately the diode impedance. It comes in parallel with existing SPICE p-i-n diode model used in CAD software. Under forward bias conditions, important recombinations occur in the heavily doped end regions of thin p-i-n diodes that seriously affects the diode impedance. This effect is taken into account to increase the accuracy of existing numerical models and to extend their validity domain to any I-region thicknesses. This improvement has been validated by measurement results on a 5-mum I-region width silicon p-i-n diode [ABSTRACT FROM PUBLISHER]

We demonstrate a high-speed GaN-based light-emitting diode at a wavelength of around 500 nm for the application to plastic optical fiber communication. By use of the n-type doping in the GaN barrier layers of the InxGa1-xN-GaN-based multiple-quantum-well (MQW), superior performance of modulation-speed (120 versus 40 MHz) and output power to the undoped control under the same bias current has been observed. According to the measured electrical-to-optical bandwidths and extracted RC-limited bandwidths of both devices, the superior speed performance can be attributed to higher electron/hole radiative recombination rate in the n-doped MQW than that of undoped MQW [ABSTRACT FROM PUBLISHER]

A comprehensive model for photomixing phenomenon in a dc-biased ultrafast photoconductor is proposed. The dependence of the carrier lifetime and carrier velocity on the electric field is taken into account, and the significance of carrier transport and carrier generation and recombination mechanisms in a terahertz photomixer are evaluated. A method for calculating the nonuniform induced electric field due to excess charge density resulting from unequal electron and hole recombination lifetimes is presented [ABSTRACT FROM PUBLISHER]

The recombination lifetime of metal-organic chemical vapor deposition grown InGaAsN-GaAsP-GaAs lasers with nitrogen content of 0% and 0.5% has been investigated from below threshold modulation frequency response measurements. Using an analysis that removes the contribution of electrical parasitic effects from the measured lifetime, it is shown that the recombination lifetime is significantly reduced when nitrogen is added into the quantum well. Furthermore, it is shown that this reduction is mainly the result of approximately a factor of four increase in the monomolecular recombination rate. [ABSTRACT FROM PUBLISHER]

The dependence of radiative recombination rate and efficiency on GaN quantum-dot (QD) size and temperature is studied by time-resolved photoluminescence (PL) spectroscopy. The emission is dominated by radiative recombination at low temperatures (<125 K) and exhibits high PL efficiency at room temperature. The radiative lifetime and the relative quantum efficiency decrease with the decreasing QD size. [ABSTRACT FROM PUBLISHER]

A thick gold layer is deposited on indium tin oxide (ITO) to improve the interface quality between the ITO anode and the organic layer in organic light-emitting diodes (LEDs). With this improvement, the device with structure ITO/Au/hole-transport-layer(HTL)/poly(p-phenylenevinylene)/Ca/Ag, achieved a lower turn-on voltage from 4 V to about 1.6 V and an increase in luminescence intensity by more than a factor of two at the same voltage. The work function of the Au facilitates the formation of an ohmic contact and good mechanical adhesion to the HTL. The experimental results suggest that the ITO contact limits the supply of current for radiative recombination. The improvement of the device performance is due to the smoother Au surface and the matching of the Au work function with the highest occupied molecular orbital level of adjacent HTL layer. [ABSTRACT FROM PUBLISHER]

We propose a type-II AlGaAsSb-AlGaInAs heterostructure superlattice for improved electronically tunable laser diodes exploiting the free-carrier plasma effect. In electronically tunable laser diodes, commonly type-I heterostructure diodes (e.g., GaInAsP-InP) are used as tuning region; however, at equal tuning, the type-II heterostructure superlattices provide the advantage of significantly smaller recombination rates due to the spatial separation of electrons and holes. As a consequence, the required tuning currents can be reduced and the maximum achievable carrier density in an optimized type-II diode can be enhanced by about a factor of two. [ABSTRACT FROM PUBLISHER]

We have extracted the ratio between the carrier capture and escape times, η, for In0.25Ga0.75As-GaAs lasers containing one, two, or three quantum wells, from high-frequency subthreshold impedance measurements at different temperatures. Our results show that the carrier capture process dominates over the diffusion along the confinement region in the overall transport/capture process. The obtained value for η is comparable to unity, and this fact has to be taken into account to obtain real material parameters, such as the carrier lifetime and the radiative recombination coefficient [ABSTRACT FROM PUBLISHER]