Optimization Of P-type Doping Process And Characterization For Semi-polar AlGaN Materials

The AlGaN-based deep ultraviolet light emitting diodes?DUV-LEDs?are of enormous potential applications in sterilization,medical treatment,air and water purification,and high density storage.Currently,the DUV-LEDs are generally manufactured with the polar c-plane AlGaN-based nitrides.However,the internal quantum efficiency?IQE?of the c-plane AlGaN based DUV-LEDs is limited owing to the intense spontaneous and piezoelectric polarization-induced quantum-confined Stark effect?QCSE?along the[0001]growth direction.In contrast,the polarization fields for the semi-polar plane AlGaN materials could be suppressed effectively because the direction of the polarization fields is tilted to the growth direction.Thus,the semi-polar AlGaN material is an ideal candidate for the fabrication of UV-LEDs.In this thesis,metal-organic chemical vapor deposition?MOCVD?technique was used to grow semi-polar?11???2?plane AlGaN epi-layers on?10???0?m-plane sapphire substrates,and their properties were systematically characterized and analyzed.At the same time,the p-type doping process of semi-polar?11???2?plane AlGaN materials was also studied.The main contents and achievements of this thesis are as follows:1.The growth and characterization of semi-polar?11???2?plane AlGaN epi-layers with different MgN insertion layers and HT-AlN buffer layers were studied extensively.The influence of the inserted layers and the buffer layers on the background electron concentrations and surface morphology of semi-polar?11???2?plane AlGaN epi-layers were studied with atomic force microscopy?AFM?,scanning electron microscopy?SEM?,and Hall effect measurement;2.The impact of the growth pressure and ?/? ratio on the background electron concentrations in semi-polar?11???2?plane AlGaN epi-layers was thoroughly studied.It was verified that the crucial influential factor on the background electron concentration in the semi-polar?11???2?plane AlGaN epi-layers was indeed the anisotropy in the 2D-growth rate,based on the characterization results of Hall effect measurement,AFM,photoluminescence?PL?,high resolution X-ray diffraction?HR-XRD?.Actually,by carefully suppressing the anisotropy in the growth rate,the background electron concentration in semi-polar Al_0.3Ga_0.7N epi-layers was reduced successfully from 1.38×10¹⁹ to 4.20×10¹⁵ cm^-3,which should meet the requirement for p-type doping;3.Consider the effects of different growth parameters on the background electron concentrations,surface roughness,and crystal quality of semi-polar?11???2?plane AlGaN epi-layers,the growth of p-type semi-polar?11???2?AlGaN epi-layers was carried out with the optimized growth parameters that could not only suppress the background electron concentrations,but also ensure the p-type doping of epi-layers.The p-type doping method adopted in this study was reformed Mg-delta doping technology.The effects of the flow rate of the Cp₂Mg on the electrical properties of the semi-polar?11???2?plane AlGaN epi-layer were also studied.