Growth Process And Optoelectronic Properties Of High-quality GaN-based Materials

This thesis is mainly divides into two major parts:the first part illustrates research on the growth of semi-polar GaN and InGaN multiple quantum wells (MQWs) on sapphire substrates by facet-controlled epitaxial lateral overgrowth in metal organic chemical vapor deposition (MOCVD) system. The samples of GaN and InGaN MQWs grow under different condition. We draw a conclusion on the microstructure, luminescence properties and stress distribution by studying those samples'optical feature and surface morphology.(1) The influence of quality of GaN on graphics sapphire substrates has been analyzed. It shows that the "dump" graphic on sapphire has been available to lower dislocation density GaN layer and higher output power in light emitting diode has size 1×1cm2 chip device.(2) The optimization of semi-polar (11-22) facet GaN on sapphire substrate in growth temperature has been explored. It indicates that a smoother surface and better morphology of semi-polar GaN has been obtained in low temperature than in high temperature because the growth of low temperature environment can not only eliminate the migration of SiO2, but also reduce the probability of overgrowth. It also illustrates that the compressive stress of semi-polar GaN gradually decreases along the growth direction.(3) The study on structural and optical properties of semi-polar InGaN quantum wells is confirmed that the growth temperature can adjust the emission wavelength of InGaN.(4) When comparing the growth properties of deep-wavelength InGaN multi-quantum wells on coalescence with non-coalescence of semi-polar GaN, we will find the growth on the coalescence of GaN can transmit a wider color gamut. The tuning of emission wavelength and the multi-color emission has been achieved by using deep-shallow InGaN quantum well system with different indium composition.The second part is to demonstrate the growth techniques for high quality GaN on Si via MOCVD. Around the difficulties of GaN layer on Si substrate fabrication, we have done a lot of research and achieved some amazing results are as following:Firstly, the optimization of pre-deposition Al time on Si substrate is investigated. The study shows that the deposition time of Al on Si will affect the quality and surface of GaN layer greatly, however, with the different buffer layer; the time is not the same. There is no need pre-deposition A1 when high temperature (HT) A1N is the buffer layer.Secondly, the influence of the growth thickness of A1N buffer layer on the properties of GaN expilayer has been surveyed.The optimum thickness of HT-A1N and low temperature (LT) A1N has a range. The HT-A1N buffer is more conducive to the growth of GaN layer than LT-A1N buffer. The research is also concluded that the optimization of A1N buffer growth is essential for separation of Ga and Si and epitaxy of GaN.Thirdly, the design of strain-relaxed interlayer structures is applied to eliminate cracks in GaN epilayers caused by large tensile stress. Crack-free GaN layers over 1.8μm with high crystal quality are achieved by inserting optimal growth rate uniform graded AlxGa1-xN interlayer between GaN layer and HT-AIN/Si template. To get the 2um crack-free GaN layer on Si Substrate, the first occurrences of HT-AlN/AlxGa1-xN composite interlayers are designed for GaN growth on Si. The results is confirmed that the new interlayer structure is greatly improved the quality of GaN due to the reduced dislocation density in 2μm GaN layer.