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The effect of employing different carrier gases (H2 only and 1:1 vol% N2:H2) in the p-type GaN (p-GaN) layer on the wall-plug efficiency (WPE) of high-power light-emitting diodes (LEDs) is studied. Since GaN crystal could be a two-dimension (2-D) growth mode in H2 ambient, better quality and smoother surface of the p-GaN were obtained. The current spreading performance of the p-GaN layer using H2 alone as the carrier gas was enhanced, resulting in advanced light output power (LOP). In addition, turn-on voltage and dynamic resistance at 500 mA, which can strongly contribute to the WPE, were also reduced by 0.12 V and 0.13 Ω, respectively. The studied device with H2 as the carrier gas in the p-GaN layer (p-H2 layer) exhibits 9.5% and 12.4% improvements in LOP and WPE at 500 mA over the device (N2/H2 = 1:1), as well as significantly better electrostatic discharge robustness. Therefore, the use of a p-H2 layer can effectively improve the performance of GaN-based LEDs for high power applications.

The epitaxial growth of GaN on Si (111) substrates has been performed using plasma-assisted molecular beam epitaxy with a thin (∼19.3 nm) single-crystal layer of Sc 2 O 3 as a template/buffer layer. The structural properties and in situ epitaxial growth were studied using reflection high energy electron diffraction (RHEED), high-resolution transmission electron microscopy, and high-resolution X-ray diffraction. An orientation relationship of GaN(0 0 0 2)IISc 2 O 3 (111)∥Si(111) and GaN[1010]∥Sc 2 O 3 [422] off 60° with Si[422] was determined. The excellent growth of Sc 2 O 3 on Si and GaN on Sc 2 O 3 was achieved, as observed from streaky and bright RHEED patterns. The Sc 2 O 3 template serves as an effective barrier layer preventing diffusion of Si and Ga during the GaN growth at high temperatures under nitrogen plasma. No cracking was observed in the GaN layer with thickness around 0.2 μm when inspected with an optical microscope.

MBE-grown single-crystal Gd 2 O 3 epitaxially on GaN has exhibited excellent thermal stability, withstanding rapid thermal annealing (RTA) at 1100 °C. The high-K dielectric Gd 2 O 3 thin film 10 nm thick has a monoclinic phase with a high degree of crystallinity, characterized by X-ray diffraction using synchrotron radiation. The orientation relationship is (402) Gd2O3 ∥(0001) GaN and Gd2O3 ∥(2110> GaN . Interface between Gd 2 O 3 and GaN remains atomically sharp after the RTA, as demonstrated using X-ray reflectivity and high-resolution transmission electron microscopy. Gd 2 O 3 /GaN metal-oxide-semiconductor capacitors show well-behaved capacitance-voltage characteristics with small dispersion and hysterisis, a high dielectric constant of ∼17, and a low electrical leakage current density of 4.6 × 10 -9 A/cm 2 at 1 MV/cm.

Electrical properties and thermal stability have been studied in molecular beam epitaxy (MBE)-grown high-K dielectric Al 2 O 3 /HfO 2 on Ge substrate. An abrupt HfO 2 /Ge interface without any interfacial layer was revealed using high-resolution transmission electron microscope and angle-resolved X-ray photoelectron spectroscopy. Capacitance-voltage characteristics, exhibiting accumulation and inversion and a high K-value of about 20 for HfO 2 , and a low leakage current density at flat-band voltage +1 V of 8 x 10 -5 A/cm 2 were obtained for metal-oxide-semiconductor capacitors (MOSCAPs) of Al 2 O 3 (3.3 nm)/ HfO 2 (2.8 nm)/Ge annealed at 500 °C in N 2 ambient for 20 min. MBE-grown Al 2 O 3 /HfO 2 is the promising high-K dielectric to realize a high-performance Ge metal-oxide-semiconductor field-effect-transistor.

In this article, we report the influence of InGaP barrier layer on the performance of 1.3 μm InAsP/InP/InGaP strain-compensated multiquantum-well (SCMQW) laser diodes (LDs) grown by metalorganic chemical vapor deposition. Sharp satellite peaks with narrow width in double-crystal X-ray diffraction measurements and abrupt interface in secondary ion mass spectrometry analyses are observed, indicating that a good epitaxial-layer quality can be obtained through the use of strain-compensation coupled by InGaP barrier layers. By increasing InGaP barrier thickness to above 6 nm, a redshift of the photoluminescence peak is observed in the (1 0 0)-oriented strained layers. It is probably attributed to redistribution across the samples of the huge built-in electric field induced by the piezoelectric effect. The threshold current of InAsP/InP/InGaP SCMQW ridge-waveguide LDs decreases from 78.8 to 33.8 mA through the employ of tensile-strained InGaP barrier layer and the lasing wavelength is 1.307 μm under 44 mA. In addition, the experimental data of broad-area LDs for the InAsP/InP strained multiquantum-well and InAsP/InP/InGaP SCMQW structures are compared in detail.

Elastocaloric cooling and heating is an alternative cooling technology that has the potential to be highly efficient and environmentally friendly. Experimental results are reported for two elastocaloric regenerators made of Ni-Ti alloys in the form of parallel plates in two plate thicknesses. For the regenerator made of 0.2 mm plates, a maximum no-load temperature span of 17.6 K was achieved for an applied strain of 4.3%. For the regenerator with 0.35 mm plates, a maximum temperature span of 19.9 K was reached for a strain of 3.5%. The 0.2 mm regenerator failed after approximately 5200 cycles and the 0.35 mm regenerator failed after approximately 5500 cycles.

In this article, we report the growth and characterization of InAsP/InP strained single quantum well (SSQW), strained single quantum well (SSQW) stack, and strained multiple quantum well (SMQW) structures on (1 0 0)-oriented InP substrates grown by metalorganic chemical vapor deposition. Double-crystal X-ray diffraction, photoluminescence (PL) and transmission electron microscope (TEM) are used to characterize the strained quantum wells. The high-quality crystalline InAs y P 1 −y (72A)/InP SSQW structure with y ⩽0.36 exhibits a 9.9 meV full-width at half-maximum (FWHM) of 10 K PL spectra. The peaks in the PL spectra for SSQW stack structure with a well thickness of 8, 14, and 35 A vanish above 100, 150, and 296 K, respectively, presumably due to the decrease of photons yielded by electron–hole recombination in thinner quantum well regions on increasing the temperature. The PL peak emission energy dependence of well thickness in the InAsP/InP SSQW stack structure is in good agreement with the calculated results. In addition, the variations of the PL peak energy and FWHM in all the InAsP/InP SSQW, SSQW stack, and SMQW structures are described in detail.

An interesting AlGaInP multiple-quantum-well light-emitting diode (LED) with a direct ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. The direct ohmic contact structure is performed by the deposition of an AuBe diffused thin layer and the following activation process on the surface of a Mg-doped GaP window layer. Experimental results demonstrate that a dynamic resistance of 5.7 Omega and a forward voltage of 1.91 V, under an injection current of 20 mA, are obtained. In addition, the studied LED exhibits a higher external quantum efficiency of 9.7% and a larger maximum light-output power of 26.6 mW. The external quantum efficiency is increased by 26% under the injection current of 100 mA, as compared with the conventional LED without this structure. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior of the studied LED, under a 20-mA operation condition, is comparable to the conventional LED without this structure.

In this article, we describe the growth and characterization for 1.3 μm InAsP/InP strained multiple quantum well (SMQW) laser diodes (LDs) with separate confinement heterostructure grown at 580°C by metalorganic chemical vapor deposition. The grown strained single quantum well (SSQW) stack and strained multiple quantum well (SMQW) structures are characterized using double-crystal X-ray diffraction and photoluminescence (PL) to confirm the structural and optical qualities for practical device applications. The InAsP/InP SSQW stack grown at 580°C appears to be extremely abrupt, uniform, free of misfit dislocations and narrow PL half width. Although the InAsP/InP SMQWs grown at 580°C maintain its structural integrity throughout the deposition sequence, the slightly broader PL half width for InAsP/InP SMQW structure is attributed to the dislocations resulted from a large net strain. Laser emission can be achieved by using the InAsP/InP SMQWs and the lasing wavelength is in a good agreement with our designed structure. The experimental data of broad-area and ridge waveguide LDs are described in detail.

In this article, we investigate the influence of AlGaAs and GaP window layers on the device performance of 650 nm AlGaInP/GaInP multi-quantum-well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical-vapor deposition. The AlGaInP/GaInP MQW structure with different window layers are characterized by double-crystal X-ray diffraction, secondary ion mass spectrometry and photoluminescence. By using the AlGaAs window layer, the LEDs have a lower cut-in voltage, a smaller dynamic series resistance and a higher breakdown voltage, while the LEDs with a GaP window layer show a stronger electroluminescence intensity, a higher light output power, a higher external quantum efficiency and a slower degradation of light output with increasing bias current. These results indicate that the GaP material is more adequate to be used as a window layer for the AlGaInP optical devices.

A 1-mm2 AlGaInP light-emitting diode (LED) sandwiched by an omni-directional reflector (ODR) and current-spreading layer is presented. The vertical-conducting bottom ODR consists of p-GaP, dispersive dot-contacts of Au-AuBe-Au acting as ohmic contacts, an intermediate low-refractive index layer of indium-tin-oxide, and a silver layer. A Si substrate, which acted as a heat sink, was bonded to the ODR-covered LED structure using a metal-to-metal bonding process. It was found that the maximum output power of the ODR-LED on Si reached 304 mW at 650 mA, and the output power did not saturate up to 650-mA injection current. The external quantum efficiency of 31.8% was obtained at 100 mA, and 19.4% achieved even at currents of up to 800 mA. Furthermore, under a forward current of 350 mA, the ODR-LEDs remained highly reliable after 1000-h testing at room temperature

We have demonstrated enhanced output power from roughened GaN-based light-emitting diodes (LEDs) by using electrodeless photoelectrochemical etching with a chopped source (ELPEC-CS etching). It was found that the 20-mA output power of the ELPEC-CS treated LED (with roughened surfaces on the top p-type and bottom n-type GaN surface as well as the mesa sidewall) was 1.41 and 2.57 times as high as those LEDs with a roughened p-type GaN surface and a conventional surface, respectively. The light output pattern of the ELPEC-CS treated LED was five times greater than the conventional LED at 0deg which was caused by the roughened GaN surface that improved the light extraction efficiency of the LED

AlGaInP multiquantum-well (MQW) light-emitting diodes (LEDs), with the n-type modulation-doped (MD) structure, were grown by metal-organic vapor-phase epitaxy. On investigation, these n-type MD-MQW LEDs exhibited a higher luminescence (2.53 lm) and a higher luminous efficiency (16.05 lm/W) than those of conventional LEDs (2.04 lm and 14.49 lm/W, respectively). The junction temperature of the MD-MQW LEDs also showed the benefits of this structure over conventional LEDs with a 14 °C reduction achieved at 150 mA.

AlGaInP-AlInP multiple quantum-well (MQW) light-emitting diodes (LEDs) with n-type modulation-doped (MD) structure were grown by metal-organic vapor-phase epitaxy. Their characteristics were then evaluated using current-voltage (I-V), electroluminescence and output power measurements. Experimental results indicated that the LEDs exhibited a higher output power, a lower dynamic resistance, and a smaller wavelength variation than conventional LEDs. The n-type MD-MQW LEDs exhibited a higher external quantum efficiency (7.19%) and a larger maximum output power (14.84 mW) under the dc operation as compared to those of 6.73% and 12.55 mW for the conventional LEDs, respectively. This could be tentatively attributed to the better junction heating effect resulting from the n-type MD-MQW structure in which the electron thermal velocity is suppressed, especially at a high-level injection. These positive results could also be explained by the MD-MQW LED supplying a higher electron concentration than in the conventional structure.

We report the effect of InGaP barrier thickness on the performance of 1.3-µm InAsP/InP/InGaP strain-compensated multiple-quantum-well (SC-MQW) ridge waveguide laser diodes (LDs) grown by metalorganic chemical vapor deposition. By increasing the InGaP tensile-strained barrier thickness to above 6 nm in the InAsP/InP/InGaP SC-MQW structure, a redshift of the photoluminescence peak position can be observed due to the redistribution across the samples of the huge built-in electric field induced by the piezoelectric effect. By using the optimum thickness of 2 nm InGaP barrier layer, the threshold current decreases from 78.5 to 41.5 mA and the characteristic temperature significantly increases as compared to those of the strain-uncompensated LDs. These results indicate that an adequate thickness of tensile-strained InGaP barrier is necessary to be employed to compensate the compressive strain in the InAsP/InP alloy system for optoelectronic devices.

The performance of the AlGaAs/InGaP single‐heterostructure (SH) and AlGaAs/InGaP/AlGaAs double‐heterostructure (DH) light‐emitting diodes (LEDs) is compared. For these two types of LEDs, they have a very shining surface morphology and flat interface. However, the SH LEDs always exhibit better properties than the DH LEDs in the ideality factor, electroluminescence, light output power, and external quantum efficiency. From the x‐ray diffraction measurements, we find that the main problem for the undesirable performance of DH LEDs is attributed to the difficulty of obtaining the high quality InGaP/AlGaAs heterostructure. Furthermore, by the Auger‐depth‐profile measurements, it is found that the P atoms with a very high diffusivity will diffuse into the as‐grown AlGaAs layer during the growth of InGaP and thus destroy the heterostructure quality.

The temperature dependence of photoluminescence from the Mg‐doped In0.5Ga0.5P layers on (100) GaAs substrates grown by liquid‐phase epitaxy has been studied. At low temperature, the spectra show only two major emission peaks involving intrinsic recombination and conduction–band‐to‐acceptor transition. The intrinsic recombination dominates in the doping concentration range studied (1.0×1017–7.0×1018 cm−3) above 60 K. Below 50 K, these two peaks merged with each other when the doping concentration is higher than 1×1018 cm−3. The temperature dependence of band gap in In0.5Ga0.5P layers determined from the photoluminescence peak energy varies as 1.976 − [7.5 ×10−4 T2/(T + 500)] eV. For the moderately doped concentration (p < 1.4 × 1018 cm−3), the Mg acceptor ionization energy obtained from 50‐K photoluminescent spectra is in the range from 37 to 40 meV.

In this article we demonstrate the feasibility of growing n-AlGaAs/p-InGaP single heterostructures on a GaAs substrate by liquid-phase epitaxy. Good quality InGaP epitaxial layers as characterized by X-ray diffraction, Nomarski phase contrast microscope, photoluminescence and Hall measurements are obtained by optimizing the Ga liquid composition of 0.0093–0.0097 mole fraction in the InGaP growth solution. The minimum transition width of 200 A at the AlGaAsInGaP heterointerface is obtained by growing the AlGaAs epitaxial layer onto the as-grown InGaP layer with an 8°C supersaturation of AlGaAs growth solution. The p-n electrical junction is precisely controlled to be located at the metallurgical junction as measured by electron-beam induced current technique. Light-emitting diodes fabricated from the Al0.7Ga0.3As/In0.5Ga0.5P heterostructure have an emission peak wavelength of 660 nm. The forward-bias turn on voltage of 1.5 V with an ideality factor of 1.64 is obtained from the current-voltage measurements. The full-width at half-maximum of room-temperature electroluminescence and light output power at 100 mA of the uncoated red light-emitting diodes are 160 A and 400 μW, respectively. An external quantum efficiency of 0.3% is two-fold higher than those previously reported.

Selection of a proper supercooled temperature to grow an Al0.7Ga0.3As window layer onto an as-grown In0.5P active layer on a GaAs substrate has resulted in an improve device performance of Al0.7Ga0.3As/In0.5Ga0.5P single heterostructure light-emitting diodes. The transition width at the AlGaAs-InGaP interface is drastically reduced from 750 A to a minimum value of 200 A as the supercooled temperature of the AlGaAs melt was increased from 4 to 8°C. The light-emitting diode fabricated from this heterostructure shows a very small reverse leakage current of less than 1x10-6 A prior to breakdown and a forward-bias turn-on voltage of 1.50 V with an ideality factor of 1.64. The narrowest full width at half maximum of 160 A at 20 mA measured by room-temperature electroluminescent spectra and the strongest light output power of 400 μW at 100 mA are obtained when the AlGaAs layer was grown with this optimized supercooled temperature of 8°C. The external quantum efficiency of 0.3% is twice higher than that previously reported.

High quality Te‐doped Al0.7Ga0.3As/Mg ‐doped In0.5Ga0.5P on p‐type GaAs substrate single‐heterostructure light‐emitting diodes have been reproducibly fabricated by liquid‐phase epitaxy using a supercooling technique. The growth conditions and properties of the undoped and Mg‐ and Zn‐doped In0.5Ga0.5P layers are described in detail. The strongest photoluminescence peak intensity occurs at a hole concentration of 1×1018 cm−3 of the Mg‐doped layer. Diodes fabricated from the heterostructure are characterized by electron‐beam‐induced current, current‐voltage measurement, electroluminescence, light output power, and external quantum efficiency. By appropriately controlling the hole concentration of the Mg‐doped In0.5Ga0.5P active layer and the electron concentration of the Te‐doped Al0.7Ga0.3As window layer, the p‐n junction can be precisely located at the metallurgical junction as measured by the electron‐beam‐induced current technique. A forward‐bias turn‐on voltage of 1.5 V with an ideality factor of 1.65 a...

We have demonstrated that the threshold current of InAsP/InP strained multiple quantum well ridge-waveguide (RWG) LDs decreased significantly by applying an optimal post-growth rapid thermal annealing procedure. It was found that the PL peak wavelengths of the InAsP/InP SSQW stack only slightly shifted of 1-4 nm and the FWHMs remained almost unaffected after 700/spl deg/C RTA, indicating that interdiffusion of group-V elements did not damage the device structures.

In this article, the authors present mobility and charge density tuning for metal organic chemical vapor deposition (MOCVD)-grown double δ-doped pseudomorphic high-electron-mobility transistors (PHEMTs). Good epitaxial wafers were obtained by MOCVD as indicated by uniform and abrupt interfaces seen in measurements taken using a transmission electron microscope and two pronounced Si-δ-doped peaks in the secondary ion mass spectrometry analysis. The 1-μm-gate-length PHEMT device exhibited good dc performance with a threshold voltage of −1.34V, a maximum drain current of 570mA∕mm, and a maximum transconductance of 279mS∕mm. From the dependences of mobility and charge density between the δ-doping level and spacer layer thickness, most PHEMT design requirements in the ranges between 5750 and 7500cm2∕Vs (for mobility) and 2.4×1012 and 3.6×1012cm−2 (for charge density) can be satisfied.

We present mobility and charge density tuning for metalorganic chemical vapor deposition (MOCVD)-grown double-doped enhancement-mode (E-mode) pseudomorphic high-electron-mobility transistors (PHEMTs) by varying the supplier layer doping level and spacer layer thickness. From the resolvable Pendellosung oscillation in double-crystal X-ray diffraction measurements and a pronounced two-dimensional electron-gas peak in capacitance–voltage (C–V) analyses, good epitaxial wafers are obtained by MOCVD. The 1-µm-gate-length E-mode PHEMT device exhibits a good pinch-off characteristic with a threshold voltage of 0.025 V and a maximum transconductance of 203 mS/mm. The dependences of the pinch-off characteristic in C–V measurement on sheet carrier concentration and spacer layer thickness for E-mode PHEMT application is also described in detail.

In this article, we report the fabrication and analysis of 1.3 μm InAsP multiquantum well laser diodes (MQW LDs) with the n-type modulation-doped (MD) InAsP/InP/InGaP active region grown by metalorganic chemical vapor deposition. We theoretically analyze the threshold current density, differential quantum efficiency, internal quantum efficiency, and internal optical loss as a function of thickness and doping concentration of n-type Si-doped InGaP barrier and InP intermediate layer for the 1.3 μm MD-MQW LDs. The optimum thickness is 2 nm for the n-type doped barrier and 6.2 nm for the doped intermediate layer while remaining 4.4-nm-thick undoped in the InP intermediate layer to prevent from lateral diffusion of Si-doped atoms into the InAsP well. Besides, the optimum doping concentration of doped InGaP barrier and doped InP intermediate layer is 1×1018 cm−3. With these optimum conditions, the LDs will reduce the threshold current density and threshold gain to 0.8 kA/cm2 and 43.08 cm−1 as compared to those of 1.6 kA/cm2 and 44.1 cm−1 for the undoped active region, respectively.In this article, we report the fabrication and analysis of 1.3 μm InAsP multiquantum well laser diodes (MQW LDs) with the n-type modulation-doped (MD) InAsP/InP/InGaP active region grown by metalorganic chemical vapor deposition. We theoretically analyze the threshold current density, differential quantum efficiency, internal quantum efficiency, and internal optical loss as a function of thickness and doping concentration of n-type Si-doped InGaP barrier and InP intermediate layer for the 1.3 μm MD-MQW LDs. The optimum thickness is 2 nm for the n-type doped barrier and 6.2 nm for the doped intermediate layer while remaining 4.4-nm-thick undoped in the InP intermediate layer to prevent from lateral diffusion of Si-doped atoms into the InAsP well. Besides, the optimum doping concentration of doped InGaP barrier and doped InP intermediate layer is 1×1018 cm−3. With these optimum conditions, the LDs will reduce the threshold current density and threshold gain to 0.8 kA/cm2 and 43.08 cm−1 as compared to those ...

The authors report on the effect of rapid thermal annealing (RTA) on the performance of InAsP/InP strained multiquantum well (SMQW) laser diodes (LDs) grown by metal organic chemical vapour deposition. From the photoluminescence (PL) measurements, the optimal RTA temperature for the InAsP/InP strained single quantum well (SSQW) stack was found to be 700/spl deg/C. The 700/spl deg/C annealed SSQW stack was found to have a stronger PL peak intensity, no halfwidth broadening and small peak shift, indicating that the degree of interdiffusion of group-V elements can be much reduced. The threshold current and slope efficiency of the 700/spl deg/C RTA SMQW LDs can be reduced significantly as compared to those of as-grown LDs.

In this article, we report the influence of growth temperature on the luminescent and structural properties of InAsyP1−y/InP strained multiple quantum wells (SMQWs) and strained single quantum wells (SSQWs) grown by metalorganic chemical vapor deposition (MOCVD). The strained quantum wells are characterized by high-resolution transmission electron microscope (TEM), photoluminescence (PL), and double-crystal x-ray diffraction (DC-XRD). An AsH3/(AsH3+PH3) gas flow ratio of 0.50% and 1.48% at 580 and 650 °C growth temperatures, respectively, will result in an InAsP layer with y=0.3 solid composition. The experimental PL emission energies at 10 K at different well thicknesses for the InAsyP1−y/InP SSQWs grown at 580 and 650 °C are in well agreement with the trend of the calculated curves. The TEM lattice image of an InAsP/InP SSQW grown at 580 °C on the order of two monolayers has been demonstrated. The InAsP/InP SSQW structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocatio...