Guangdi Shen

Barrier effect on hole transport and carrier distribution in InGaN∕GaN multiple quantum well visible light-emitting diodes

Carrier distributions governed by hole transport in InGaN∕GaN multiple quantum well (MQW) visible light-emitting diodes (LEDs) were investigated using conventional blue LEDs and dual-wavelength blue-green LEDs. It was found that holes were dominantly distributed in the QW close to the p-GaN layer in LEDs with conventional MQW active regions at a current of 20mA. A decrease in the thickness or the height of the quantum-well potential barrier enhanced hole injection into the MQWs located near the n-GaN layer. Reducing the thickness of a GaN quantum-well barrier between the blue QW and green QW did not degrade the electroluminescence (EL) intensity of the LED. In contrast, reducing the potential height of the barrier with material of possibly compromised quality resulted in a degradation of the EL intensity of the LED.

Tunnel-regenerated multiple-active-region light-emitting diodes with high efficiency

Tunnel-regenerated multiple-active-region (TRMAR) light-emitting diodes (LEDs) with high quantum efficiency and high brightness have been proposed and fabricated. We have proved experimentally that the efficiency of the electrical luminescence and the on-axis luminous intensity of such TRMAR LEDs scaled linearly approximately with the number of the active regions. The on-axis luminous intensity of such TRMAR LEDs with only 3 mum GaP current spreading layer have exceeded 5 cd at 20 mA dc operation under 15 degrees package. The high-quantum-efficiency and high-brightness LEDs under the low injection level were realized

EBSD measurements of elastic strain fields in a GaN/sapphire structure

An elastic strain field of the heteroepitaxial GaN layer grown on the sapphire substrate, containing a buffer interlayer, was measured using the electron backscatter diffraction (EBSD). Pattern qualities, Hough transforms and small misorientations of Kikuchi bands on EBSD patterns, as strain sensitive parameters and referred to diffraction intensities, were performed to evaluate the elastically distorted region within the sample. The elastic strain gradient parallel to the growth direction of GaN epilayers was mapped and a strain range from 100 nm to 200 nm was detected.

Novel large-coupled optical cavity semiconductor lasers and multiactive region light-emitting diodes with high performance

Novel multi-active region semiconductor lasers with large coupled optical cavity and high quantum efficiency, and new mechanism tunneling-regenerated multi-active region light emitting diodes with high quantum efficiency and high brightness have been proposed and fabricated. The external and differential quantum efficiency are 2.9 and 3.0 W/A, and the output light power as high as approximately 5 W when the injecting current equals 2A for the four active region 980 nm strained InGaAs/GaAs QW lasers. The fundamental mode light output with perpendicular angle <EQ 17 degrees for this type of large coupled optical cavity laser has been achieved. The on-axis luminous intensity of the new mechanism 620 nm AlGaInP/AlInP LEDs with two active regions is more than 5 cd. It was theoretically and experimentally resulted in that the electro-luminescence efficiency and the on-axis luminous intensity are linearly increasing approximately with the number of the active regions.

High-power coupled large-cavity lasers and multiactive light-emitting diodes

For increasing laser diode (LD) output power, improving laser beam quality and enhancing the light emitting diode (LED) brightness, the coupled large optical cavity semiconductor lasers and multi-active LEDs with tunneling- regenerated current transport have been presented and experimented. Both the external and differential quantum efficiency and both the LDs output power and LEDs brightness are together increasing approximately with the number of the active regions. The very high power Lds and and the very high brightness LEDs working the low injecting current and also the fundamental mode stimulated light with good beam quality have been achieved in our laboratory.

High efficiency tunneling-regenerated multi-active region light-emitting diodes

A new mechanism of tunneling-regenerated multi-active region LEDs with high quantum efficiency and high brightness has been presented. The layer structure, MOCVD growth, device technology, a several of measured curves and their analysis of these new mechanism LEDs were shown in the paper. It was theoretically and experimentally resulted in that efficiency of the electro-luminescence and the on-axis luminous intensity can linearly increase approximately with the number of active regions.

The RPS method applied to the numerical solution of multimode slab waveguides with complex indexes

In order to obtain the numerical solution of multimode slab waveguides with complex indexes, we propose a method named RPS, which integrates real index numerical method, perturbation method and shooting method. This RPS method avoids searching the solution in the whole complex plane, meanwhile, it is simple, fast and precise. The application shows that the RPS method is suitable for both the transverse electric (TE) and the transverse magnetic (TM) mode.

The resistance characteristics of the Ni-Cr thin films and their influence on the integrated circuits

Ni-Cr thin films with different thicknesses have been fabricated on the dielectric substrate silicon dioxide (SiO/sub 2/) by using magnetron sputtering and vacuum evaporation and annealed at different temperatures. The sheet resistance and the strip line microwave impedance of the Ni-Cr thin film are measured. The results show that they are influenced strongly by the thickness and the annealing temperature. These problems are analyzed in detail including the effects of the carrier tunnel transport, the oxidation, the condensation and the stabilization in the thin film.

Investigation of high extraction efficiency flip-chip GaN-based light-emitting diodes

In order to obtain higher light output power, the flip-chip structure is used. We studied the ratio of the light of GaN sides before and after fabricating metal reflector on p-GaN. The SiO2/SiNx dielectric film reflectors were deposited through plasma enhance chemical vapor deposition following the fabrication of metal reflector, and then the dielectric film reflectors on the electrodes were etched in order to expose the electrodes to the air. It is found that comparing with the flip-chip GaN-LED without dielectric film reflectors, light output power can be increased by as high as 10.2% after the deposition of 2 pairs of SiO2/SiNx dielectric film reflectors on GaN-LEDs, which cover the sidewalls and the areas without the metal reflector. This result indicates that the high reflector formed by multi-layer dielectric films is useful to enhance the light output power of GaN-based LED, which reflects light from step sidewalls and p-GaN without metal reflector to internal, and then light emits from the surface.

Enhanced output of GaN-based light-emitting diodes with stripe-contact electrodes

High brightness GaN-based light-emitting diodes(LEDs) with stripe-contact electrodes have been developed. The p-type Ohmic contact layer is composed of oxidized Ni∕Au stripes and NiO stripes. A Ag (3000A) omnidirectional reflector covers the p-type contact. The n-type contact is a Ti∕Al planar film with a Ti∕Al stripe. All Ni∕Au, NiO, and Ti∕Al stripes surround the center of the LED mesa. At 20mA current operation, the light output power of GaN-based LEDs with the stripe-contact electrodes is 16.26%–35.37% higher than that of the conventional LEDs.