Study On Fabrication Of Gan-based Green LEDs On SiC Substrates

At present,group ? metal nitride semiconductor material,especially of gallium nitride(GaN),have attracted considerable interest owing to their greatly promising application value in solid state lighting.In recent years,the research on blue and red light emitting diode(LED)has made great progress,however,the research on green LED progressed slowly because InGaN active layer with high In components were difficult to fabricate.The crystal quality,interface and luminescence efficiency of InGaN active layer which have been fabricated were not approved.In the paper,metal-organic chemical vapor deposition(MOCVD)was employed to fabricate high-quality GaN template and green LED with the optimized GaN template.Crystallinity,surface morphologies,stress states,optical properties and electrical properties were examined by different analysis techniques.The main research contents are as follows:GaN template has been grown with AIN buffer on SiC substrates.The effects of AlN buffer thickness on crystallinity,optical properties and stress states of GaN template were studied in detail.Experimental results showed that the properties of GaN template achieved to the best when the thickness of AIN buffer is 120 nm.GaN template has been grown on SiC substrates with AlN buffer and step-graded AIGaN buffer with different growth temperature and NH3 flux.Experimental results demonstrated that the lower the tensile stress in GaN template,the higher the crystallinity of the template.The densities of screw and edge dislocations decreased to the best values of 7×107 and 3.1×108 cm-2.The root-mean-squared roughness value was 0.381 nm.GaN template has been further optimized with SiNx interlayer on the basis of the previous experiments.The effects of the number of SiNx interlayer on properties of GaN template were precisely investigated.We found that the tensile stress of GaN template reduced,meanwhile,epitaxial quality of GaN template was improved further with multiple SiNx interlayer.InGaN/GaN multi-quantum-well green LEDs have been prepared on the optimum GaN template with AlN buffer,step-graded AlGaN buffer and bis-layer SiNx interlayer.Photoetching,inductively coupled plasma(ICP)and evaporation coating were employed to fabricate Ni-Au electrodes of p-GaN.The influence of the number of quantum-well structure on the properties of green LED has been studied in detail.The results indicated that the lattice of MQWs was complete,the thickness of MQWs was uniform,Indium composition is about 24%-29%,threshold voltage was about 3.8 V.The LED has good rectifying feature and emits green light in PL and EL.