Design Of High Efficiency AlGaInP Light-emitting Devices

The quaternary alloy AlGaInP is a wide direct bandgap semiconductor, which is widely used in many optoelectronics devices. The high-brightness light emiting diodes (HB-LED) made from AlGaInP have been received widespread atention, because its light emission spectra extendsfrom red to yellow-green.The applications for quaternary AlGaInP HB-LEDs are in the process of being developed. Some of those applications include out-door display, automotive light, traffic signal lights, information signals.In order to improve the device performance for the requirement of new applications, much eforts have been done on the material system to design new material structure and to develop the new device processing for high efficiency in our research work.In this paper we make a series of research on the design of AlGaInP HB-LED structure, material grown by MOCVD and the epitaxy processing.1.Theoretical analysis and efficiency measurement:Spontaneous emission spectrum of AlGaInP material was calculated theroetically and make in-depth analysis of intenal quantum efficiency based on recombination mechanisms in LEDs.A measurement of internal quantum efficiency was raised. The changes of external quantum efficiency over the temperature range from 30K to 300K are measured, and the external quantum efficiency increases with decreasing temperature firstly and then reaches maximum value and gets saturated. The IQE is attained by analyzing various recombination mechanisms in LEDs. The light extraction efficiency is calculated by a ray-tracing simulation taking into account the influence of photon recycling. Then analyze the IQE from the relations of extraction efficiency and external quantum efficiency.2.Optimize.material epitaxy : The heavily p-type AlGaInP epitaxy layer was discussed deeply and the affect of Al composition and substrate temperature on p-type AlGaInP epitaxy layer were observed in experiment and explained qualitatively. Hole concentration would increase severalfold after anneal processing and excessed 1×10¹⁸cm^-3 . A special method of high quality GaP cap layer which grown on AlGaInP epitaxy layer was innovated. The surface of GaP epitaxy layer is mirror-like only with some pinstripe and hole concentration reached 1×10¹⁹cm^-3. Afte some reliability analysis of GaP cap layer processing,the result was very optimistic.