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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.

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 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.

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.

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...