Search

In this paper, InGaAs p-i-n photodetectors (PDs) on an InP/SiO2/Si (InPOI) substrate fabricated by ion-slicing technology are demonstrated and compared with the identical device on a commercial InP substrate. The quality of epitaxial layers on the InPOI substrate is similar to that on the InP substrate. The photo responsivities of both devices measured at 1.55 µm are comparable, which are about 0.808–0.828 A W−1. Although the dark current of PD on the InPOI substrate is twice as high as that of PD on the InP substrate at 300 K, the peak detectivities of both PDs are comparable. In general, the overall performance of the InPOI-based PD is comparable to the InP-based PD, demonstrating that the ion-slicing technology is a promising route to enable the high-quality Si-based InP platform for the full photonic integration on a Si substrate. [ABSTRACT FROM AUTHOR]

In this work, (-2 0 1) β-Ga2O3 films are grown on GaN substrate by metal organic chemical vapor deposition (MOCVD). It is revealed that the β-Ga2O3 film grown on GaN possesses superior crystal quality, material homogeneity and surface morphology than the results of common heteroepitaxial β-Ga2O3 film based on sapphire substrate. Further, the relevance between the crystal quality of epitaxial β-Ga2O3 film and the β-Ga2O3/GaN interface behavior is investigated. Transmission electron microscopy result indicates that the interface atom refactoring phenomenon is beneficial to relieve the mismatch strain and improve the crystal quality of subsequent β-Ga2O3 film. Moreover, the energy band structure of β-Ga2O3/GaN heterostructure grown by MOCVD is investigated by X-ray photoelectron spectroscopy and a large conduction band offset of 0.89 eV is obtained. The results in this work not only convincingly demonstrate the advantages of β-Ga2O3 films grown on GaN substrate, but also show the great application potential of MOCVD β-Ga2O3/GaN heterostructures in microelectronic applications. [ABSTRACT FROM AUTHOR]

After the carrier drift velocity at the semiconductor / metal interface is considered, current transport in Schottky diodes under a forward electric field is physically modelled. This model reveals that the ideality factor can be physically originated from the drift velocity and the drift velocity can also reduce the effective Schottky barrier height. This proposed model predicts that both the ideality factor and the Schottky barrier height depend on temperature, voltage and doping density, which agree well with the experimental results reported in the literature. The proposed diode current model also predicts a linear dependent relation between the reciprocal of the ideality factor and the effective Schottky barrier height, which is validated by experimental results. Such a model is useful to better understand the thermionic emission current physically in semiconductor / metal contact. It is also useful to characterise the material properties by using the ideality factor. [ABSTRACT FROM AUTHOR]

Au/polymer P2ClAn(H3BO3)/n-GaAs Schottky barrier diodes, where P2ClAn stands for poly(2-chloroaniline), have been fabricated. To fabricate Schottky diodes with polymer interface, n-type GaAs wafer was used. The P2ClAn polymer solution was applied on the front face of the n-GaAs wafer by a pipette. The P2ClAn emeraldine salt was chemically synthesized by using boric acid (H3BO3). Schottky diode parameters, such as ideality factor, barrier height and series resistance have been measured, as functions of hydrostatic pressure, using the current-voltage technique. The ideality factor values of Au/P2ClAn/n-GaAs Schottky barrier diodes have decreased from 3.38 to 3.01, the barrier height has increased from 0.653 to 0.731 eV at 0.36 kbar and series resistances were ranging from 14.95 to 14.69. The results obtained from I-V characteristics of Au/P2ClAn/n-GaAs Schottky barrier diodes show that pressure treatment improves the rectifying properties of the diodes. These diodes can be used as pressure-sensitive capacitors, due to pressure-dependence of diode parameters. [ABSTRACT FROM AUTHOR]

Gallium doped cadmium-oxide (CdO: Ga) thin films were successfully deposited by sol-gel spin coating method on p-type Si substrate. The electrical properties of the photodiode based on nanostructure Ga doped n-CdO/ p-Si junctions were investigated. The current-voltage ( I- V) characteristics of the structure were investigated under various light intensity and dark. It was observed that generated photocurrent of the Au/ n-CdO/p-Si junctions depended on light intensity. The capacitance-voltage and conductance-voltage measurements were carried out for this diode in the frequency range between 100 and 1000 kHz at room temperature by steps of 100 kHz. The capacitance decreased with increasing frequency due to a continuous distribution of the interface states. These results suggested that the Au/ n-CdO/ p-Si Schottky junctions could be utilized as a photosensor. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C- V and G/ω-V measurements and plotted as functions of voltage and frequency. The distribution profile of R - V gave a peak in the depletion region at low frequencies and disappeared with increasing frequencies. [ABSTRACT FROM AUTHOR]

We have investigated the electrical properties and current transport mechanisms of W/ p-InP Schottky diode using current-voltage ( I- V), capacitance-voltage-frequency ( C- V- f) and conductance-frequency ( G- f) techniques at room temperature. The W/ p-InP Schottky diode exhibits a good rectifying behavior. Measurements show that the Schottky barrier height (SBH) and ideality factor of the W/ p-InP Schottky diode are 0.84 eV ( I- V)/0.98 eV ( C- V) and 1.24, respectively. Also, the SBH and series resistance R of the diode are extracted by Cheung's functions and the values are in good agreement with each other. Ohmic and space charge-limited conduction mechanisms are found to govern the current flow in the W/ p-InP Schottky diode at low and high forward bias conditions, respectively. Experimental results reveal that the Poole-Frenkel mechanism is found to be dominant in the reverse bias region of W/ p-InP Schottky diode. Further, the interface state density N and their relaxation times τ of the W/ p-InP Schottky diode are estimated from the forward bias C- f and G- f characteristics and the values are in the range from 1.95 × 10 eV cm and 3.38 × 10 s at (0.81- E) eV to 1.78 × 10 eV cm and 2.78 × 10 s at (0.30- E) eV, respectively. Both the N and τ show an exponential rise with bias from the top of the valance band toward the mid gap. [ABSTRACT FROM AUTHOR]

In this study, titanium nitride (TiN) is synthesized using reactive sputtering for a self-aligned gate process. The Schottky barrier height of the TiN on n-GaN is around 0.5 to 0.6 eV and remains virtually constant with varying nitrogen ratios. As compared with the conventional Ni electrode, the TiN electrode presents a lower turn-on voltage, while its reverse leakage current is comparable with that of Ni. The results of annealing evaluation at different temperatures and duration times show that the TiN/W/Au gate stack can withstand the ohmic annealing process at 800°C for 1 or 3 min. Finally, the self-aligned TiN-gated AlGaN/GaN heterostructure field-effect transistors are obtained with good pinch-off characteristics. [ABSTRACT FROM AUTHOR]

Theoretical investigations of Cr doped GaAs in zinc blende phase are presented in this paper. The robustness of half metallicity of these compounds with correlation to their lattice compressions is discussed. Shifting of Fermi Level with compression of lattice constant is also addressed in this article. Results show that compounds exhibit their half-metallic nature (conductor for spin up state and semiconductor for spin down state) with their lattice compressions up to certain critical lattice constants. Abrupt changes in electronic and magnetic properties are observed for these robust transition lattice constants (RTLCs). These compounds lose their integer magnetic moments 4μ at RTLCs. Calculated RTLC for GaCrAs is 5.03 Å. Possible compressions in lattice constants from their relaxed states while maintaining their half-metallic nature is up to 4 %. [ABSTRACT FROM AUTHOR]

In this paper, a new gate-recessed AlGaN/GaN-based high electron mobility transistor (HEMT) on SiC substrate is proposed and its DC as well as microwave characteristics are discussed for SiN and SiO passivation layers using technology computer aided design (TCAD). The two-dimensional electron gas (2DEG) transport properties are discussed by solving Schrödinger and Poisson equations self-consistently resulting in various subbands having electron eigenvalues. From DC characteristics, the saturation drain currents are measured to be 600 mA/mm and 550 mA/mm for SiN and SiO passivation layers respectively. Apart from DC, small-signal AC analysis has been done using two-port network for various microwave parameters. The extrinsic transconductance parameters are measured to be 131.7 mS/mm at a gate voltage of V = −0.35 V and 114.6 mS/mm at a gate voltage of V = −0.4 V for SiN and SiO passivation layers respectively. The current gain cut-off frequencies ( f) are measured to be 27.1 GHz and 23.97 GHz in unit-gain-point method at a gate voltage of −0.4 V for SiN and SiO passivation layers respectively. Similarly, the power gain cut-off frequencies ( f) are measured to be 41 GHz and 38.5 GHz in unit-gain-point method at a gate voltage of −0.1 V for SiN and SiO passivation layers respectively. Furthermore, the maximum frequency of oscillation or unit power gain (MUG = 1) cut-off frequencies for SiN and SiO passivation layers are measured to be 32 GHz and 28 GHz respectively from MUG curves and the unit current gain, ∣ h ∣ = 1 cut-off frequencies are measured to be 140 GHz and 75 GHz for SiN and SiO passivation layers respectively from the abs ∣ h ∣ curves. HEMT with SiN passivation layer gives better results than HEMT with SiO passivation layer. [ABSTRACT FROM AUTHOR]

Comparative study of the photoluminescence (PL) from quantum wells (QWs) in forward-biased p-GaN/InGaN/ n-GaN structures and electroluminescence from these structures has been carried out. It is shown that, upon application of a forward bias, a characteristic red shift of the spectral peak is observed, together with a broadening of the PL line and simultaneous burning-up of the PL. This results from a decrease in the field strength in the space charge region of the p- n junction and suppression of the tunneling leakage of the carrier from band-tail states in the active InGaN layer. An analysis of the results obtained demonstrated that the tunneling strongly affects the quantum efficiency and enabled evaluation of the internal quantum efficiency of the structures. It is shown that nonequilibrium population of band-tail states in InGaN/GaN QWs depends on the injection type and is controlled by the capture of carriers injected into a QW, in the case of optical injection, and by carrier tunneling “below” the QW under electrical injection. [ABSTRACT FROM AUTHOR]

The nature of the external quantum efficiency’s drop in the AlInGaN-based light-emitting diode’s heterostructures at high pumping has been considered. The temperature dependence of the external quantum efficiency has been investigated for two types of heterostructures with an active region located in the n- and p-type regions. It is found experimentally that the temperature dependence of the external quantum efficiency at high pumping for these two types of heterostructures is different. It is shown by numerical simulation that this difference is due to the unlikely behavior of the carrier injection’s efficiency into the active region of heterostructures with n- and p-type active regions. The results obtained indicate a key role of the injection mechanism in the drop of the external quantum efficiency at high pumping. [ABSTRACT FROM AUTHOR]

The effect of the properties of interfaces with Group-III phosphides on characteristics of GaInP solar cells has been studied. It is shown that the large valence band offset at the p-GaAs/ p-AlInP interface imposes fundamental limitations on the use of p-AlInP layers as a wide-band-gap window in p- n structures of solar cells operating at ratios of high solar light concentration. It is demonstrated that characteristics of p-n solar cells can be, in principle, improved by using a double-layer wide-band-gap window constituted by p-Al0.8Ga0.2As and p-(Al0.6Ga0.4)0.51In0.49P layers. [ABSTRACT FROM AUTHOR]

Heterostructures with single strained InGaAs/GaAs quantum wells have been studied by measuring the capacitance-voltage characteristics in a wide range of temperatures and test signal frequencies. Based on the analysis of experimental capacitance-voltage characteristics, a temperature shift of the peak in the apparent profile of a majority carrier’s concentration is revealed and a quantitative model of this phenomenon is proposed. The effect of incomplete impurity ionization on the experimentally found quantum well’s charge is determined. It is established by numerical simulation and fitting of capacitance-voltage characteristics that the conduction band’s discontinuity for heterostructures with strained In xGa1 − xAs/GaAs quantum wells ( x = 0.225) remains constant and equal to 172 ± 10 meV at temperatures from 320 to 100 K. [ABSTRACT FROM AUTHOR]

The electric characteristics of the p+- i- n+ structures are analyzed for two types of GaAs epitaxial layers: the structures with an i layer based on undoped GaAs and an i layer based on GaAs:Cr. The forward currents of the first-type diodes are caused by recombination in the space-charge region. The reverse I–V characteristics at the voltages to 10–15 V are determined by the component of the generation current. At | U| > 20 V, the current growth is caused by the Poole-Frenkel effect, which is replaced by electron tunneling through the potential-barrier top with increasing the voltage as a result of the electron-phonon interaction. The forward branches of the I–V characteristics of the p+- i- n+ diodes with the i layer based on GaAs:Cr are explained by the unipolar injection in the semiconductor, which is replaced by the bipolar injection with increasing the voltage. The reverse I–V characteristics are linear in the range of 1–15 V; at | U| > 20 V, an increase in current is caused by the impact ionization. [ABSTRACT FROM AUTHOR]

Technological modes in which high-efficiency GaAs: Si/GaAs: C tunneling structures can be fabricated by MOS-hydride epitaxy have been determined. It was demonstrated that use of C and Si dopants makes it possible to obtain a p-n junction with low diffusion spreading of dopant profiles. It was shown that fabrication of high-efficiency tunnel diodes requires that GaAs layers should be doped with acceptor and donor impurities to a level of ∼9 × 1019 cm−3. Tunnel diodes were fabricated using the tunnel structures and their current-voltage characteristics were studied. Peak current densities Jp ≈ 1.53 kA cm−2 and a differential resistance R ≈ 30 mΩ under a reverse bias were obtained in the tunnel diodes. [ABSTRACT FROM AUTHOR]

It is shown that it is possible to grow a continuous series of (GaSb)1 − x (Si2) x ( x = 0−1) alloys on silicon substrates by the method of liquid-phase epitaxy from a tin solution—melt. The X-ray patterns and the spectral and current-voltage characteristics of the obtained p-Si- n-(GaSb)1 − x (Si2) x in the temperature range of 20–200°C are studied. An extended section of the type V ∞ exp( JaW) corresponding to the effect of injection-caused depletion is observed in the current-voltage characteristics. [ABSTRACT FROM AUTHOR]

In this article, a novel InGaP/GaAs pnp δ-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a δ-doped sheet between two spacer layers at the emitter-base (E-B) junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and a relatively low E-B offset voltage of 60 mV are achieved. The offset voltage is much smaller than the conventional InGaP/GaAs pnp HBT. The proposed device could be used for linear amplifiers and low-power complementary integrated circuit applications. [ABSTRACT FROM AUTHOR]

The control effect of the ferroelectric polarization on the two-dimensional electron gas (2DEG) in a ferroelectric/AlGaN/GaN metal–ferroelectric–semiconductor (MFS) structure is theoretically analyzed by a self-consistent approach. With incorporating the hysteresis nature of the ferroelectric into calculation, the nature of the control effect is disclosed, where the 2DEG density is depleted/restored after poling/depoling operation on the MFS structure. The orientation of the ferroelectric polarization is clarified to be parallel to that of the AlGaN barrier, which, based on an electrostatics analysis, is attributed to the pinning effect of the underlying polarization. Reducing the thickness of the AlGaN barrier from 25 nm to 20 nm leads to an improved control modulation of the 2DEG density from 36.7% to 54.1%. [ABSTRACT FROM AUTHOR]

The effect of negative resistivity observed at anomalously low voltages in output characteristics of modulation-doped In0.53Ga0.47As/In0.52Al0.48As field-effect transistors is considered. In the discussed experiments, the threshold for appearance of negative resistivity depends not only on the gate length, which was mentioned before, but also on the gate-drain voltage. It is shown that the negative differential resistivity observed at output characteristics of the short-channel In0.53Ga0.47As/In0.52Al0.48As field-effect transistor at anomalously low threshold voltages is related to the formation of the second transport channel as a result of resonance transition of hot electrons from upper levels of the quantum well to the above-barrier layer via the states of ionized donor impurity. The results of the analysis of the low-frequency experiment are used to interpret splitting of the line of emission of the short-channel transistor in the region of terahertz frequency. [ABSTRACT FROM AUTHOR]

Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V, has been studied. The resistanceless J-V j characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-V j characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-VOC, and the dependence of the luminescence intensity on the forward current L-J. Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-V j characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation ( C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation. [ABSTRACT FROM AUTHOR]

The influence of some parameters of nitrogen-containing heterostructures InAs/GaAsN/InGaAsN with strain-compensated superlattices (SCSL) on their emission characteristics has been studied. It is established that the net strain in the structure affects the photoluminescence (PL) linewidth, internal quantum efficiency, intensity, and wavelength. The maximum PL intensity and minimum full width at half maximum (FWHM) of the PL line were achieved with small strains (0–0.2%), whereas the maximum wavelengths (∼1.76 μm) observed for large strain (about +1%). By adding multilayer InAs inserts in the active InGaAsN quantum well in combination with using strain-compensated GaAsN/InGaAsN superlattices, it is possible to control the room-temperature emission wavelength in the range of 1.45–1.76 μm without significantly deteriorating the emissiion characteristics. [ABSTRACT FROM AUTHOR]

Simulation of multicomponent AlInGaN-based heterostructures for their use in light-emitting diodes is performed. The effect of nonuniform distribution of In atoms in the light-emitting “nanodiodes” on the working characteristics of the device in general are determined. A model describing the structure of multicomponent AlInGaN heterostructures for light-emitting diodes is developed. [ABSTRACT FROM AUTHOR]

Resonance detection of terahertz radiation by submicrometer field-effect GaAs/AlGaAs transistors (with the gate length L = 250 nm) with two-dimensional electron gas in the channel has been studied at T = 4.2 K. For these transistors, it is shown for the first time that the maximum of the response (the drain-source photovoltage) shifts with an increasing frequency to the region of higher gate voltages in accordance with the Dyakonov-Shur theory. It is shown that, as temperature is increased to 77 K, the dependence of the photovoltage on the gate voltage becomes nonresonant, which is caused by a decrease in the mobility. [ABSTRACT FROM AUTHOR]

It is experimentally found that the maximum drift velocity of electrons in quantum wells of differently arranged AlGaAs/GaAs heterostructures and pseudoamorphous Al0.36Ga0.64As/In0.15Ga0.85 As heterostructures is higher than the maximum drift velocity of electrons in bulk materials. It is established that no negative differential conductivity is exhibited by the field dependence of the drift velocity of two-dimensional electrons in GaAs and In0.15Ga0.85As. The drift velocity in the GaAs quantum well is saturated in fields several times higher than the field corresponding to the Γ- L intervalley transitions of electrons in bulk GaAs. [ABSTRACT FROM AUTHOR]

Spectral, current-voltage, and light-current characteristics of p-InAsSbP/ n-InGaAsSb/ n+-InAs narrow-gap diode structures with 130 × 130 μm lateral dimensions of active elements are presented. The 2D distribution of light emitted by the samples fabricated in the form of emitting flip-chip 1 × 4 arrays is examined, including analysis of the emission uniformity. The limiting effective temperature created by an emitter of this type is determined. [ABSTRACT FROM AUTHOR]

We describe experiments investigating the quality of ohmic contacts to both bulk GaN and to III-nitride heterostructures. Titanium-based contacts were investigated to assess the role of intermixing and surface impurities for contact formation to n-type GaN. Direct contact to the two-dimensional electron gas in GaN/AlGaN heterostructures was also studied. These contacts were made by photochemical etching of the samples to expose the heterointerface. It was observed that even in the latter case contact annealing leads to a lower contact resistance by consuming surface contaminants and promoting beneficial interfacial reactions. Various passivation techniques were tried to reduce surface leakage current between contact pads and PECVD-deposited silicon nitride was found to be the best material for this application. [ABSTRACT FROM AUTHOR]

The photoresponse time of the cyclotron resonance detector to terahertz radiation under integer quantum Hall effect conditions in the GaAs/AlGaAs heterostructure is shown to have a deep minimum at the Hall plateau center and two sharp maxima at the plateau edges. The minimum at the plateau center is associated with the fundamental property of vanishing of the random impurity potential screening under quantum Hall effect conditions. The decrease in the response time outside the plateau is related to the equilibrium population of the Landau level above (under) the Fermi level by electrons (holes), respectively, which increases the probability of photoexcited carrier recombination. It is shown that, under conditions of background radiation (300 K), relaxation times decrease by two orders of magnitude while retaining the characteristic magnetic field dependence. [ABSTRACT FROM AUTHOR]

The efficiency of photoconversion in solar cells based on GaAs with InGaAs quantum wells under the AM 1.5 conditions for various levels of base doping has been simulated using the software package Sim-Windows. The results obtained are compared with the efficiency of photoconversion in conventional solar cells. It is shown that solar cells with quantum wells can exhibit a fairly high efficiency of photoconversion in comparison with the photoconversion efficiency of conventional solar cells under the following conditions: (i) the lifetimes of for charge carriers in the quantum wells are longer than those in the barrier material and (ii) the level of doping of the base is not very high. It is established that the maximum efficiency of photoconversion in conventional solar cells is higher than the photoconversion efficiency in solar cells with quantum wells. This efficiency is attained at high doping levels in the base (∼3 × 1018 cm−3 at the parameters used in calculations). This is related to a more intense radiative recombination and also to specific features of screening and charge transport in solar cells with quantum wells at high doping levels. It is shown that, at fairly large values for the degree of concentration of incident radiation, the values for the photoconversion efficiency in solar cells with quantum wells for the low and high levels of doping of the base come closer to each other. [ABSTRACT FROM AUTHOR]

For field-effect transistors based on heterostructures with selective doping, the results of calculations for the output characteristics of devices on the basis of the hydrodynamic model are compared with those based on the quasi-hydrodynamic (temperature-related) model. It is shown that the transverse spatial transport and heavy dependences of relaxation times on energy lead to the situation where the results of calculations based on the above models differ appreciably from one another at the gate lengths that much exceed the length of electron relaxation by momentum. [ABSTRACT FROM AUTHOR]

The effect of heating of electrons and holes on the nonideality coefficient of the current-voltage characteristic for a p-n junction in a high microwave field is studied. It is established that the nonideality coefficient for a diode depends on the type of charge carriers that make the major contribution to the current in the p-n junction. It is shown that, in some cases in silicon samples, the nonideality coefficient for the diode is governed by the temperature for holes in spite of the fact that the temperature for electrons is higher than the temperature for holes. [ABSTRACT FROM AUTHOR]

Layers of the GaSb1 − x As x alloy with arsenic content in the range x = 0.06–0.15 have been grown for the first time on InAs (100) substrates by metal-organic vapor-phase epitaxy. A new approach to the calculation of the band diagram of the GaSbAs alloy is suggested. It is demonstrated on the basis of magnetotransport measurements in p-GaSbAs/ p-InAs heterostructures and with the method suggested by the authors for the calculation of band diagrams for alloys in the GaSbAs system that, in the composition range under study, the GaSbAs/InAs heterojunction is a type II broken-gap heterojunction. [ABSTRACT FROM AUTHOR]

We have studied the electrical characteristics of photodiodes based on p-GaSb/ p-GaInAsSb/ N-GaAlAsSb heterojunctions and investigated the mechanisms of current transfer in these heterostructures at various temperatures. A comparison of the theoretical results and experimental data showed that the tunneling charge transfer mechanism dominates at low temperatures ( T < 150 K) under both forward and reverse bias conditions. The tunneling current becomes a determining factor at an electric field strength in the p- n junction of no less that 105 V/cm, which is related to a small bandgap width of the materials studied and low effective masses of electrons and holes. [ABSTRACT FROM AUTHOR]

The current-voltage and brightness-voltage characteristics and the electroluminescence spectra of blue InGaN/GaN-based light-emitting diodes are studied to clarify the cause of the decrease in the emission efficiency at high current densities and high temperatures. It is found that the linear increase in the emission intensity with increasing injection current changes into a sublinear increase, resulting in a decrease in efficiency as the observed photon energy shifts from the mobility edge. The emission intensity decreases with increasing temperature when the photon energy approaches the mobility edge; this results in the reduction in efficiency on overheating. With increasing temperature, the peak of the electroluminescence spectrum shifts to lower photon energies because of the narrowing of the band gap. The results are interpreted taking into account the fact that the density-of-states tails in InGaN are filled not only via trapping of free charge carriers, but also via tunneling transitions into the tail states. The decrease in the emission efficiency at high currents is attributed to the suppression of tunneling injection and the enhancement of losses via the nonradiative recombination channel “under” the quantum well. [ABSTRACT FROM AUTHOR]

The formation of axial heterostructures in filamentary nanocrystals (nanowhiskers) is considered within the framework of a two-component diffusion growth model. An expression for the thickness of a heteroboundary is obtained, which is consistent with the available experimental data. Under the usual growth conditions, the thickness of the zone of diffusion smearing of the heteroboundary is on the order of one atomic monolayer, which ensures the high quality of heteroboundaries in nanowhiskers. [ABSTRACT FROM AUTHOR]

Studies of the properties of InGaAsN compounds and methods of controlling the emission wavelength in InAs/GaAsN/InGaAsN heterostructures grown by molecular beam epitaxy on GaAs substrates are reviewed. The results for different types of heterostructures with quantum-size InGaAsN layers are presented. Among those are (1) traditional InGaAsN quantum wells in a GaAs matrix, (2) InAs quantum dots embedded in an (In)GaAsN layer, and (3) strain-compensated superlattices InAs/GaAsN/InGaAsN with quantum wells and quantum dots. The methods used in the study allow controllable variations in the emission wavelength over the telecommunication range from 1.3 to 1.76 μm at room temperature. [ABSTRACT FROM AUTHOR]

Structural and electrical properties of Au-TiB x - nn + n ++-InP and TiB x - nn + n ++-InP multilayer barrier structures on standard (“rigid”) and soft (“porous”) n ++-InP substrates have been studied, with the semiconductor layers deposited by vapor-phase epitaxy, metallic layers formed by magnetron sputtering, and porous substrates fabricated by electrochemical etching of the standard InP. Samples on porous substrates have the following advantages: leakage currents in their reverse current-voltage characteristics are ten times lower; the range of the exponential rise in current in the forward characteristics is an order of magnitude wider; the changes in the ideality factor and the Schottky barrier height, observed as the contact area varies by a factor of 100, are three and ∼10 times smaller, respectively; and the structure of the layers is more stable in annealing at up to 800°C. [ABSTRACT FROM AUTHOR]

The crystal structure and surface morphology of native oxide emerging on the surface of the (0001) cleavage of undoped and Cd-doped or Dy-doped single crystals of layered GaSe due to prolonged storage in air are studied. The factors that lead to the differences in the outward appearance of oxide films on the surface of undoped (dull surface) and doped samples (transparent films) are analyzed. The results of studies of electrical properties of the 〈gallium selenide〉-〈native oxide〉 systems are reported. It is shown that the films of native oxide on the GaSe surface feature current instability with an N-like current-voltage characteristic. Attention is paid to low values of effective permittivity of native oxide. [ABSTRACT FROM AUTHOR]

The dc performances of an InP/InGaAs pnp heterostructure-emitter bipolar transistor are investigated by theoretical analysis and experimental results. Though the valence band discontinuity at the InP/InGaAs heterojunction is relatively large, the addition of a heavily-doped as well as thin p +-InGaAs emitter layer between p-InP confinement and n +-InGaAs base layers effectively eliminates the potential spike at emitter-base junction and simultaneously lowers the emitter-collector offset voltage and increases the potential barrier for electrons. Experimentally, a high current gain of 88 and a low offset voltage of 54 mV have been achieved. [ABSTRACT FROM AUTHOR]

We have studied the influence of structural design on the optical properties of heterostructures comprising InAs quantum wells (QWs) and quantum dots (QDs) in strain-compensated GaAsN/InGaAsN superlattices. It is established that, using such superlattices with various QW and barrier thicknesses and different numbers (from one to three) InAs inserts in the active region, it is possible to control the wavelength of room-temperature emission within 1.3–1.76 μ m without deteriorating the output radiation characteristics. [ABSTRACT FROM AUTHOR]

The magnetoresistance oscillations that occur in a two-dimensional electron system exposed to strong microwave radiation when the microwave frequency ω coincides with the nth subharmonic of the cyclotron frequency ω c have been investigated for n = 2, 3, and 4. It is shown that these subharmonic features can be explained within a nonequilibrium energy distribution function picture without invoking multiphoton absorption processes. The existence of a frequency threshold above which such oscillations disappear lends further support to this explanation. [ABSTRACT FROM AUTHOR]

Confinement and localization of optical phonons in narrow phonon wells with thin phonon barriers decreases the rate of electron-phonon scattering by polar optical phonons by a factor of many times. An increase in mobility and drift velocity of electrons is experimentally observed in strong electric fields upon introduction of thin phonon barriers into the AlGaAs/GaAs/AlGaAs quantum well. [ABSTRACT FROM AUTHOR]

It is shown that capture of the surface (interface) phonons can occur in a double-barrier heterostructure in addition to the capture of bulk polar optical phonons. The strength of interaction of electrons with confined interface phonons becomes lower as the thickness of the phonon well (a semiconductor layer where phonons are captured) is decreased. A new approach is suggested for reducing the scattering of electrons by polar optical phonons in a double-barrier quantum well; this approach is based on separate capture of phonons in narrow phonon wells. The calculated scattering rate with the capture of interface phonons into the GaAs/InAs/GaAs and AlAs/GaAs/AlAs quantum wells taken into account is found to be much lower than the rate obtained in the approximation of scattering of electrons by bulk phonons. A multifold decrease in the rate of electron-phonon scattering in the AlAs/GaAs/AlAs quantum well is obtained by separating this well by the monomolecular InAs layer that is transparent for electrons but acts as a reflecting barrier for polar optical phonons. [ABSTRACT FROM AUTHOR]

The properties of multiple-junction solar cells depend on the properties of the constituent photovoltaic and tunneling p-n junctions. In this study, the properties of the space-charge region for photovoltaic and tunneling p-n junctions were examined using the dark current-voltage characteristics for two semiconductors: GaSb (a narrow-gap semiconductor) and GaAs (a wide-gap semiconductor). The effects of irradiation with protons (the energy of 6.78 MeV and the maximum fluence of 3 × 1012 cm−2), electrons (the energy of 1 MeV and the maximum fluence of 3 × 1016 cm−2), and γ-ray photons (the energy of 1.17–1.33 MeV and the maximum dose of 17 Mrad) on the lifetime of charge carriers in the space-charge region of photovoltaic p-n junctions and on the peak current of connecting tunneling p-n junctions were studied. The coefficients of the damage for the inverse lifetime are determined for photovoltaic p-n junctions. The coefficients of equivalence between the used types of radiation are determined; these coefficients are found to be almost independent, on the order of magnitude, of the type and material of the p-n-junction (and nearly equal for photovoltaic GaAs p-n junctions and tunneling GaAs and GaSb p-n junctions). [ABSTRACT FROM AUTHOR]

The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications. [ABSTRACT FROM AUTHOR]

White electroluminescence (EL) from ZnO/GaN structures fabricated by pulsed laser deposition of ZnO:In onto GaN:Mg/GaN structures MOCVD-grown on Al2O3 substrates has been observed. The white light is produced by superposition of the two strongest emission lines, narrow blue and broad yellow, peaked at 440 and 550 nm, respectively. The intensity ratio of different EL lines from ZnO/GaN/Al2O3 structures depends on the ZnO film quality and drive current. The white EL is due to the high density of structural defects at the n-ZnO/ p-GaN interface. A band diagram of the n-ZnO/ p-GaN/ n-GaN structure is constructed and a qualitative explanation of the EL is suggested. [ABSTRACT FROM AUTHOR]

The Fourier spectra of oscillations of magnetoresistance in the heavily doped Al x Ga1 − x As:Si/GaAs heterostructure, with filling of the two size-quantization subbands, the ground subband E m and the excited subband E p , are studied. In the concept of the probabilities of intrasubband and intersubband transitions involving the Landau levels, the origin of harmonics at the frequencies F m ± F p in the oscillations of magnetoresistance are interpreted. The ratio between the peak amplitudes A m and A p at the frequencies F m and F p of the harmonics is close to unity, with equal probabilities of the relations A m / A p > 1 and A m / A p < 1. At A m / A p > 1, the damping of the Landau quantization is controlled by the Coulomb potential, whereas at A m / A p < 1 it is controlled by relaxation of two-dimensional electrons due to the heterointerfacial roughness. [ABSTRACT FROM AUTHOR]

Simulation methods based on the energy-balance equation are used to study the electrical conductivity of layered nanosized heterostructures in high electric fields. A quasi-hydrodynamic description of the electron drift is used with regard to the diffusion and thermal-diffusion components of the current, the divergence of the electron heat flux, and the temperature dependence of the electron mobility and energy relaxation time. Current-voltage characteristics are obtained for a layered heterostructure with a barrier height of 0.3 eV and with lengths of both the narrow-and wide-gap layers equal to 50 nm. Depending on the doping level in the range (5–1) × 1017 cm−3, the characteristics exhibit either a sharp peak of the differential conductivity or a bistability loop corresponding to the thermal-injection instability. A physical model is suggested that attributes the shape of the calculated current-voltage characteristics to the cumulative effect of the electrostatic lowering of the heterobarrier height and the increase in electron temperature near the injecting heteroboundaries. [ABSTRACT FROM AUTHOR]