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In this paper, a theory is developed to study the anisotropic scattering effect of the inclined misfit dislocation on the two-dimensional electron gas in Al(In)GaN/GaN heterostructures. The inclined misfit dislocation, which differs from the well-known vertical threading dislocation, has a remarkable tilt angle from the vertical. The predicted electron mobility shows a remarkable anisotropy. It has a maximum mobility value along the direction perpendicular to the projection of the inclined dislocation line, and a minimum mobility value along the direction parallel to the projection. The degree of the anisotropic scattering effect will be even greater with the increase of the tilt angle. [ABSTRACT FROM AUTHOR]

In this letter, quantum cascade lasers (QCLs) based on excited-states injection are presented. The operating voltage is significantly reduced compared with the conventional groundstate injection design. Devices emitting at ~5.25 μm were fabricated through standard buried-heterostructure processing. Stable single-mode emission was observed by implementing a buried first-order distributed feedback (DFB) grating. The maximum output power of the DFB QCL with 2-mm cavity length was more than 300 mW at 10 °C with a high wall-plug efficiency of 5.6% in continuous-wave mode. [ABSTRACT FROM AUTHOR]

We demonstrate a buried grating coupled substrate emitting distributed-feedback quantum cascade laser with high power room temperature continuous wave (cw) operation at 4.97 μm. A second-order semiconductor/semiconductor grating is used for in-plane feedback and vertical out-coupling. A surface emitting power of 248 mW is attained in cw operation at 20 °C. Single-mode operation is obtained with a good linear wavelength tuning with injection current. The far field shows a low divergence about 0.14° × 16°, indicating that the device operates in symmetric mode. [ABSTRACT FROM PUBLISHER]

We demonstrate a quantum dot quantum cascade photodetector with a hybrid active region of InAs quantum dots and an InGaAs quantum well, which exhibited a temperature independent response at 4.5 lm. The normal incident responsivity reached 10.3 mA/W at 120 K and maintained a value of 9 mA/W up to 260 K. It exhibited a specific detectivity above 1011 cm Hz1/2 W-1 at 77 K, which remained at 108 cm Hz1/2 W-1 at 260 K. We ascribe the device's good thermal stability of infrared response to the three-dimensional quantum confinement of the InAs quantum dots incorporated in the active region. [ABSTRACT FROM AUTHOR]

A phase-locked quantum cascade laser (QCL) array consisting of one hundred elements that were integrated in parallel was achieved at λ ~ 4.6 μm. The proposed Fraunhofer's multiple slits diffraction model predicted and explained the far-field pattern of the phase-locked laser array. A single-lobed far-field pattern, attributed to the emission of an in-phase-like supermode, is obtained near the threshold (Ith). Even at 1.5 Ith, greater than 73.3% of the laser output power is concentrated in a low-divergence beam with an optical power of up to 40 W. [ABSTRACT FROM AUTHOR]

A coupled ridge waveguide quantum cascade laser (QCL) array consisting of fifteen elements with parallel integration was presented. In-phase fundamental mode operation in each element is secured by both the index-guided nature of the ridge and delicate loss management by properly designed geometries of the ridges and interspaces. Single-lobe lateral far-field with a nearly diffraction limited beam pattern was obtained. By incorporating a one-dimensional buried distributed feedback grating, the in-phase-operating coupled ridge waveguide QCL design provides an efficient solution to obtaining high output power and stable single longitudinal mode emission. The simplicity of this structure and fabrication process makes this approach attractive to many practical applications. [ABSTRACT FROM AUTHOR]

We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 μm. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski-Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64×1011 and 4.83×106 Jones at zero bias were obtained at 80K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging. [ABSTRACT FROM AUTHOR]

We report a beam reshaping phenomena via nanopore array defined on the emission window of a substrate emitting quantum cascade lasers. A pronounced beam divergence reduction by a factor of 6 in the elongated beam direction is achieved. A collimated laser beam with small divergence (2.9° × 0.12°) is observed. These single-mode devices preserve good power and spectral performances at room temperature continuous wave operation. This beam reshaping design is simple to fabricate and able to be adapted for other wavelengths ranging from the visible to mid-infrared regimes, which would open up major opportunities for the control of beam divergence. [ABSTRACT FROM AUTHOR]

The effects of V/III growth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated. The surface morphology, crystalline quality, strain states, and density of basal stacking faults were found to depend heavily upon the V/III ratio. With decreasing V/III ratio, the surface morphology and crystal quality first improved and then deteriorated, and the density of the basal-plane stacking faults also first decreased and then increased. The optimal V/III ratio growth condition for the best surface morphology and crystalline quality and the smallest basal-plane stacking fault density of a-GaN films are found. We also found that the formation of basal-plane stacking faults is an effective way to release strain. [ABSTRACT FROM AUTHOR]

We designed and fabricated a six-channel complex-coupled distributed feedback (DFB) quantum cascade laser arrays based on a sampled Bragg grating. The six-channel DFB laser arrays exhibit a linear tuning range of 74 nm centered at a wavelength of 7.55 μm at room temperature. Robust single-mode emission with a side mode suppression ratio about 20 dB was observed, even at full power. The used sampled grating and reflectivity coating on the back facet lead to the peak output power varying from 55 to 82mW with a small difference in slope efficiency from 100 to 128mW/A. [ABSTRACT FROM AUTHOR]

The mobility limited by cluster scattering in ternary alloy semiconductor quantum wire (QWR) is theoretically investigated under Born approximation. We calculate the screened mobility due to clusters (high indium composition InGaN) scattering in the InxGa1−xN QWR structure. The characteristics of the cluster scattering mechanism are discussed in terms of the indium composition of clusters, the one-dimensional electron gas (1DEG) concentration, and the radius of QWR. We find that the density, breadth of cluster, and the correlation length have a strong effect on the electron mobility due to cluster scattering. Finally, a comparison of the cluster scattering is made with the alloy-disorder scattering. It is found that the cluster scattering acts as a significant scattering event to impact the resultant electron mobility in ternary alloy QWR. [ABSTRACT FROM AUTHOR]

Homoepitaxial growth of 4H-SiC epilayers is conducted in a SiH4-C2H4-H2 system by low pressure hot-wall vertical chemical vapor deposition (CVD). Thick epilayers of 45 μm are achieved at a high growth rate up to 26 μm/h under an optimized growth condition, and are characterized by using a Normaski optical microscope, a scanning electronic microscope (SEM), an atomic force microscope (AFM) and an x-ray diffractometer (XRD), indicating good crystalline quality with mirror-like smooth surfaces and an rms roughness of 0.9 nm in a 5 μm × 5μm area. The dependence of the 4H-SiC growth rate on growth conditions on 4° off-axis 4H-SiC substrates and its mechanism are investigated. It is found that the H2 flow rate could influence the surface roughness, while good surface morphologies without Si droplets and epitaxial defects such as triangular defects could be obtained by increasing temperature. [ABSTRACT FROM AUTHOR]

Broadband light emission is obtained from a chirped multiple InAs/InGaAs/GaAs quantum dot (QD) structure. The thickness of the InGaAs strain-reducing layer (SRL) is used as the tuning parameter to adjust the light emission property of each QD layer in the chirped structure. It is shown from the photoluminescence (PL) measurement that the SRL thickness has a strong influence on the PL peak position, linewidth, and intensity. By constructing the chirped QD structure comprising five groups of QD layers with different SRL thicknesses, a broadband electroluminescence emission with the full width at half maximum of 202 nm is realized, indicating the feasibility of chirped multiple InAs QD layers on broadening the emission spectrum. [ABSTRACT FROM AUTHOR]

A mode-locked external-cavity laser emitting at 1.17-μm wavelength using an InAs/GaAs quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated. By changing the external-cavity length, repetition rates of 854, 912, and 969 MHz are achieved respectively. The narrowest −3-dB radio-frequency linewidth obtained is 38 kHz, indicating that the laser is under stable mode-locking operation. [ABSTRACT FROM AUTHOR]

By using x-ray diffraction analysis, we investigate the major structural parameters such as strain state and crystal quality of non-polar a-plane InxGa1−xN thin films grown on r-sapphire substrates by metalorganic chemical vapour deposition. The results of the inplane grazing incidence diffraction technique are analyzed and compared with a complementary out-of-plane high resolution x-ray diffraction technique. When the indium composition is low, the a-plane InxGa1−xN layer is tensile strain in the growth direction (a-axis) and compressive strain in the two in-plane directions (m-axis and c-axis). The strain status becomes contrary when the indium composition is high. The stress in the m-axis direction σyy is larger than that in the c-axis direction σzz. Furthermore, strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the InxGa1−xN film. [ABSTRACT FROM AUTHOR]

The optical performance of a grating-coupled external cavity laser based on InAs/InP quantum dots is investigated. Continuous tuning from 1391 nm to 1468 nm is realized at an injection current of 1900 mA. With the injection current increasing to 2300 mA, the tuning is blue shifted to some extent to the range from 1383 nm to 1461 nm. By combining the effect of the injection current with the grating tuning, the total tuning bandwidth of the external cavity quantum-dot laser can reach up to 85 nm. The dependence of the threshold current on the tuning wavelength is also presented. [ABSTRACT FROM AUTHOR]

Low-density (∼109 cm−2), long-wavelength (more than 1300 nm at room temperature) InAs/GaAs quantum dots (QDs) with only 1.75-mono-layer (ML) InAs deposition were achieved by using a formation-dissolution-regrowth method. Firstly, small high-density InAs QDs were formed at 490°C, then the substrate temperature was ramped up to 530°C, and another 0.2 ML InAs was added. After this process, the density of the InAs QDs became much lower, and their size became much larger. The full width at half maximum of the photoluminescence peak of the low density, long-wavelength InAs QDs was as small as 27.5 meV. [ABSTRACT FROM AUTHOR]

Metalorganic chemical vapor deposition growth of InAs/GaSb superlattices is reported using an AsxSb1-x plane that connects the InAs and GaSb layers to compensate the tensile strain introduced by the InAs layers. The effects of gas switching sequences for growing the AsxSb1-x planes on the interface structure and crystalline quality of InAs/GaSb superlattices were investigated by Raman scattering spectroscopy and X-ray diffraction. It is found that uniform interfaces and high-quality superlattice can be obtained by growing the AsxSb1-x planes through the exchange interaction of As and Sb atoms at the surfaces of InAs or GaSb layers. [ABSTRACT FROM AUTHOR]

Semi-polar ZnO (10&bar11;) epitaxial films are demonstrated using a methanol oxidant by metalorganic chemical vapor deposition on Si (111) substrates at 500°C. X-ray Ø scanning indicates that there are six kinds of in-plane domain growths, with the ZnO [10&bar12;] parallel to the Si <11&bar2;> direction families. The crystallographic orientation of ZnO is supposed to be caused by surface passivation. The methanol, as a polar molecule, may be adsorbed on the Si (111) surface to form a passivation layer, which inhibits the (0001) ZnO plane deposition on the substrate surface, and as a result the ZnO (10&bar11;) plane becomes preferred. The optical properties, examined by a roomtemperature photoluminescence spectrum, exhibit a strong near-band-edge emission peak at 379 nm, indicating that the (10&bar11;) ZnO film has good crystal quality. These results are significant for research into and for the applications of semi-polar ZnO films. [ABSTRACT FROM AUTHOR]

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energy E b and spin-orbit split energy Г of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well $$ \overline{\text{W}} $$ decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Г decreases drastically. (4) The maximum of Г is 1.22 meV when the electric field of heterointerface is 1 MV/cm. [ABSTRACT FROM AUTHOR]

This work discusses the fabrication of two-dimensional photonic crystal mask layer patterns. Photonic crystal patterns having holes with smooth and straight sidewalls are achieved by optimizing electron beam exposure doses during electron beam lithography process. Thereafter, to precisely transfer the patterns from the beam resist to the SiO2 mask layer, we developed a pulse-time etching method and optimize various reaction ion etching conditions. Results show that we can obtain high quality two-dimensional photonic crystal mask layer patterns. [ABSTRACT FROM AUTHOR]

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The absorption of valacyclovir presents a highly negative correlation with the level of P-glycoprotein expression. • It has been confirmed that a polymorphism of the MDR1 gene in exon 26 is related to the level of P-glycoprotein expression in intestine. • This study was conducted to find the relationship between polymorphism of MDR1 gene and absorption of valacyclovir. WHAT THIS STUDY ADDS • Linkage disequilibrium exists between G2677T/A in exon 21 and C3435T in exon 26, between C1236T in exon 12 and C3435T, but not between C1236T and G2677T/A of MDR1 gene in the Chinese Han ethnic population. • Three single nucleotide polymorphisms of MDR1 gene do not influence the absorption of valacyclovir in the healthy Chinese Han ethnic population. AIMS To investigate the influence of three single nucleotide polymorphisms (SNPs) in exon 12 (C1236T), exon 21 (G2677T/A) and exon 26 (C3435T) of MDR1 gene on the absorption of valacyclovir after a single oral administration in the Chinese Han ethnic population. METHODS Two hundred healthy Chinese subjects were genotyped for the SNPs of C1236T, G2677T/A and C3435T in the MDR1 gene using allele-specific polymerase chain reaction. Linkage disequilibrium (LD) was analysed. Twenty-four subjects derived from a large random sample ( n = 200) received a single oral dose of 600 mg valacyclovir. Plasma concentrations of acyclovir were determined up to 14 h after administration to obtain a pharmacokinetic profile. RESULTS LD existed between G2677T/A in exon 21 and C3435T in exon 26 ( P < 0.001), between C1236T in exon 12 and C3435T ( P < 0.001), but not between C1236T and G2677T/A ( P > 0.05). Cmax, AUC0–1.5 h and AUC0–∞ were used as indices of valacyclovir absorption. AUC0–∞ for the 2677TA genotype was 17.45 ± 2.40 µg × h/ml, which was much higher compared with the 2677GG, GA and TT genotypes of 10.44 ± 1.00, 11.84 ± 2.83, 11.34 ± 2.32 µg × h/ml, respectively ( P < 0.05). Similarly, a statistically significant difference of AUC0–∞ was also observed for different linked genotypes at position 2677 vs. 3435, and 1236 vs. 3435 ( P < 0.05). However, there was no significant difference in valacyclovir absorptive pharmacokinetics between carriers and noncarriers of different haplotypes ( P > 0.05). CONCLUSIONS Three SNPs of MDR1 gene did not influence the absorption of a single oral dose of 600 mg valacyclovir in healthy Chinese Han ethnic subjects. [ABSTRACT FROM AUTHOR]

High-power broad area substrate-emitting distributed feedback (DFB) quantum cascade laser emitting at λ ~ 4.6 μm is reported. Proper second-order DFB grating coupling, low waveguide loss mechanism, and epilayer-down mounting bring about a high vertical radiative optical power. The maximum peak power is as high as 1.82 W at 20 °C and still 1.22 W at 50 °C operated in pulsed mode with a pulsed width of 1 μs and duty cycle of 0.2%. A single-lobed radiation far-field with a divergence angle of 7.9 ° in the ridge-width direction and two-lobed radiation far-field with a divergence angle of 0.61 ° in the cavity-length direction are achieved by depositing the high-reflection coatings on both facets. Robust single-mode emission is continuously tunable by the heat sink temperature up to 115 °C. [ABSTRACT FROM PUBLISHER]

We investigate the triangular defects with different structural features on 4H-SiC epilayers by a Nomarski microscope, a Candela optical surface analyzer and ultraviolet photoluminescence (UV-PL) imaging. Both the foreign particles and the substrate scratches can cause the formation of the obtuse triangular defects. The central area of some obtuse triangular defects can have the spatially confined core, in which the in-grown stacking faults can be observed under the UV-PL imaging. In contrast, the obtuse triangular defects induced by the scratches appear in the form of band-like defects, of which the width depends on the scratch direction and reaches the maximum when the scratch direction is parallel to the step flow direction. The formation mechanisms of these obtuse triangular defects are discussed. [ABSTRACT FROM AUTHOR]

We present a surface metal grating distributed feedback quantum cascade laser emitting at &lgr;∼8.3&mgr;m and operating above 400K in pulsed mode. A very high peak power of 463mW at 290K and still more than 18mW at 400K is achieved for a high-reflectivity-coated 13-&mgr;m-wide and 2.5-mm-long laser. Single-mode emission with a high side mode suppression ratio and wide temperature tuning range is observed. Such a high-power single-mode laser with a simple device process is important for practical applications. [ABSTRACT FROM AUTHOR]

We demonstrate room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers emitting at 4.7 μm. A rectangular photonic crystal lattice perpendicular to the cleaved facet was defined using holographic lithography. The anticrossing of the index- and Bragg-guided dispersions of rectangular lattice forms the band-edge mode with extended mode volume and reduced group velocity. Utilizing this coupling mechanism, single mode operation with a near-diffractive-limited divergence angle of 12° is obtained for 33 μm wide devices in a temperature range of 85–300 K. The reduced threshold current densities and improved heat dissipation management contribute to the realization of devices’ room temperature operation. [ABSTRACT FROM AUTHOR]

Fascinating features of porous InP array-directed assembly of InAs nanostructures are presented. Strained InAs nanostructures are grown by molecular-beam epitaxy on electrochemical etched porous InP substrate. Identical porous substrate with different pore depths defines different growth modes. Shallow pores direct the formation of closely spaced InAs dots at the bottom. Deep pores lead to progressive covering of the internal surface of pores by epitaxial material followed by pore mouth shrinking. For any depth an obvious dot depletion feature occurs on top of the pore framework. This growth method presages a pathway to engineer quantum-dot molecules and other nanoelements for fancy physical phenomena. [ABSTRACT FROM AUTHOR]

Analyzes the effectivity of photoluminescence in identifying optical properties of gallium[sub 0.5]indium[sub0.5]phosphorous (GaInP[sub2]) epitaxial layers. Relevance of temperatures and excitation densities on optical properties; Creation of a quantum well structure model; Use of metalorganic vapor phase epitaxy for the growth of GaInP[sub 2] samples.

Examines the influence of DX centers on low-temperature density and mobility of two-dimensional electron gas (2DEG) in gallium arsenide/aluminum gallium arsenide heterostructure. Adoption of a triangular quantum well approximation; Factors limiting the 2DEG mobility; Agreement of calculated and experimental results.

Examines interface roughness scattering on the mobility of two-dimensional electron gas (2DEG) in GaAs-AlGaAs modulation-doped heterostructures. Dominance of scattering in 2DEG density; Comparison between interface roughness and alloy disorder scattering.

The spin-polarized photocurrent is used to study the in-plane electric field dependent spin transport in undoped InGaAs/AlGaAs multiple quantum wells. In the temperature range of 77–297 K, the spin-polarized photocurrent shows an anisotropic spin transport under different oriented in-plane electric fields. We ascribe this characteristic to two dominant mechanisms: the hot phonon effect and the Rashba spin-orbit effect which is influenced by the in-plane electric fields with different orientations. The formulas are proposed to fit our experiments, suggesting a guide of potential applications and devices. [ABSTRACT FROM AUTHOR]

Metal organic chemical vapor deposition (MOCVD) growth systems are one of the main types of equipment used for growing single crystal materials, such as GaN. To obtain film epitaxial materials with uniform performance, the flow field and temperature field in a GaN-MOCVD reactor are investigated by modeling and simulating. To make the simulation results more consistent with the actual situation, the gases in the reactor are considered to be compressible, making it possible to investigate the distributions of gas density and pressure in the reactor. The computational fluid dynamics method is used to study the effects of inlet gas flow velocity, pressure in the reactor, rotational speed of graphite susceptor, and gases used in the growth, which has great guiding significance for the growth of GaN film materials. [ABSTRACT FROM AUTHOR]

As one of the most important tumor-associated antigens of colorectal adenocarcinoma, the carcinoembryonic antigen (CEA) threatens human health seriously all over the globe. Fast electrical and highly sensitive detection of the CEA with AlGaN/GaN high electron mobility transistor is demonstrated experimentally. To achieve a low detection limit, the Au-gated sensing area of the sensor is functionalized with a CEA aptamer instead of the corresponding antibody. The proposed aptasensor has successfully detected different concentrations (ranging from 50 picogram/milliliter (pg/ml) to 50 nanogram/milliliter (ng/ml)) of CEA and achieved a detection limit as low as 50 pg/ml at . The drain-source current shows a clear increase of 11.5 μA under this bias. [ABSTRACT FROM AUTHOR]

AlGaN epitaxial layer has been studied by means of temperature-dependent time-integrated photoluminescence (PL) and time-resolved photoluminescence (TRPL). An enhancing redshift phenomenon in TRPL spectra with increasing temperature was observed, and the localized excitons behaved like quasi two-dimensional excitons between 6 K and 90 K. We demonstrated that these behaviors are caused by a change in the carrier dynamics with increasing temperature due to the competition of carriers’ localization and delocalization in the AlGaN alloy. [ABSTRACT FROM AUTHOR]

Two kinds of InAs/GaAs quantum dot (QD) structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the GaAs barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs. [ABSTRACT FROM AUTHOR]

Gallium nitride- (GaN) based high electron mobility transistors (HEMTs) provide a good platform for biological detection. In this work, both Au-gated AlInN/GaN HEMT and AlGaN/GaN HEMT biosensors are fabricated for the detection of deoxyribonucleic acid (DNA) hybridization. The Au-gated AlInN/GaN HEMT biosensor exhibits higher sensitivity in comparison with the AlGaN/GaN HEMT biosensor. For the former, the drain-source current ( V) shows a clear decrease of 69 μA upon the introduction of 1 μmolL(μM) complimentary DNA to the probe DNA at the sensor area, while for the latter it is only 38 μA. This current reduction is a notable indication of the hybridization. The high sensitivity can be attributed to the thinner barrier of the AlInN/GaN heterostructure, which makes the two-dimensional electron gas channel more susceptible to a slight change of the surface charge. [ABSTRACT FROM AUTHOR]

An external cavity quantum cascade laser (QCL) array with a wide tuning range and high output power is presented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capability of 30.6 cm−1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications. [ABSTRACT FROM AUTHOR]

We report on the design and fabrication of λ ∼ 7.2 μm distributed feedback quantum cascade lasers for very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90°C. For a 2-mm-long and 10-μm-wide laser coated with high-reflectivity on the rear facet, more than 170 mW of output power is obtained at 20°C with a threshold power consumption of 2.4 W, corresponding to 30mW with a threshold power consumption of 3.9 W at 90°C. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) grown on Fe-modulation-doped (MD) and unintentionally doped (UID) GaN buffer layers are investigated and compared. Highly resistive GaN buffers (109 Ω·cm) are induced by individual mechanisms for the electron traps' formation: the Fe MD buffer (sample A) and the UID buffer with high density of edge-type dislocations (7.24 × 109 cm−2, sample B). The 300 K Hall test indicates that the mobility of sample A with Fe doping (2503 cm2V−1s−1) is much higher than sample B (1926 cm2V−1s−1) due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage (−2.63 V) compared with device B (−3.71 V). Lower gate leakage current |IGS| of device A (3.32 × 10−7 A) is present compared with that of device B (8.29 × 10−7 A). When the off-state quiescent points Q2 (VGQ2 = −8 V, VDQ2 = 0 V) are on, Vth hardly shifts for device A while device B shows +0.21 V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance Gm−VGS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress. [ABSTRACT FROM AUTHOR]

The exciton–phonon interaction in Al0.4Ga0.6N/Al0.53Ga0.47N multiple quantum wells (MQWs) is studied by deep-ultraviolet time-integrated and time-resolved photoluminescence (PL). Up to four longitudinal-optical (LO) phonon replicas of exciton recombination are observed, indicating the strong coupling of excitons with LO phonons in the MQWs. Moreover, the exciton–phonon coupling strength in the MQWs is quantified by the Huang–Rhys factor, and it keeps almost constant in a temperature range from 10 K to 120 K. This result can be explained in terms of effects of fluctuations in the well thickness in the MQWs and the temperature on the exciton–phonon interaction. [ABSTRACT FROM AUTHOR]

We demonstrate continuous-wave (CW) high power-efficiency terahertz quantum cascade laser based on semi-insulating surface-plasmon waveguide with epitaxial-side down (Epi-down) mounting process. The performance of the device is analyzed in detail. The laser emits at a frequency of ∼ 3.27 THz and has a maximum CW operating temperature of ∼ 70 K. The peak output powers are 177 mW in pulsed mode and 149 mW in CW mode at 10 K for 130-μm-wide Epi-down mounted lasers. The record wall-plug efficiencies in direct measurement are 2.26% and 2.05% in pulsed and CW mode, respectively. [ABSTRACT FROM AUTHOR]

Double-wavelength intersubband electroluminescence at ∼7 and ∼10 µm was obtained using a simple five-well quantum cascade structure. Electron injection from a common injector level to two neighboring emitting wells was realized by resonant tunneling or phonon-assisted tunneling, determined by the energy separation between the injector level E0 and the upper-emitting levels under various bias electric fields. Such simple quantum cascade structures might lead to a new solution for dual-color mid-infrared lasers. [ABSTRACT FROM AUTHOR]

A strain-compensated InP-based quantum cascade laser (QCL) structure emitting at 4.6 μm is demonstrated, based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy (MBE). By optimizing the growth parameters, a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated. Threshold current densities as low as 0.47 kA/cm2 in pulsed operation and 0.56 kA/cm2 in continuous-wave (cw) operation at 293 K were achieved for this state-of-the-art QCL. A minimum power consumption of 3.65 W was measured for the QCL, uncooled, with a high-reflectivity (HR) coating on its rear facet. [ABSTRACT FROM AUTHOR]