Improving GaN Thin Film Crystalline Quality By High Temperature Pre-growth

GaN,Which is representive of third generation semiconductor materials, has been appliedin solid State Lighting and electronic information. As a new generation of solid-state lightingsource, GaN-based LEDs become the focus of current research, but LED chips performancecould not achieve the people’s goal, among various factors the most important is that peoplecould not produce high quality GaN thin films.Based on the existing wafer growth process, before the epitaxy of low-temperature bufferlayer, the patterned sapphire substrate was prepared by a pre-growth treatment with a smallamount of trimethyl gallium (TMGa) and a great quantity of ammonia (NH3) at a hightemperature. Four types of blue light-emitting diode (LED) wafers with different growth timewere fabricated. It was shown that as the growth time increased, the PL and EL intensity fellafter the first rise. At20mA, high temperature pre-growth samples could increase the lightoutput power by14.9%which compares to the traditional sample, while the forward woltagewas significantly reduced.High temperature pre-growth blue LED samples with different flow-rate of TMGa on thepatterned sapphire substrate were further studied, and four samples with different flow-rate ofTMGa were fabricated. The interference graph of GaN thin film showed that the hightemperature pre-growth could benefit the lateral growth of three-dimensional GaN islands inepitaxy and leads to fast coalescence from three-dimensional to two-dimensional GaN. Thephotoluminescence spetrum and high resolution XRD results showed the threadingdislocation could be suppressed and the quality of epitaxial film would be improved. Theenhancement of light-output power of LED chips could be raised up to29.1%withoutdegradation of electrical performance, but the improvement effect would decrease with theincreasing of TMGa flow.A p-InGaN layer and a p-GaN transition layer were inserted between the last multiplequantum barrier and p-AlGaN electron blocking layer to improve wafer’s lighting property.Three samples with different Cp2Mg flow were fabricated by MOCVD. Metalloscope andphotoluminescence spetrum were used to perform the surface morphology and light-outputperformance of the samples. It was found that the Cp2Mg flow had an significantly effect onsurface morphology and PL intensity. With the rise of Cp2Mg flow, the samples’ surfacebecame rough and PL intensity began to decrease.