Study On Epitaxial Growth And P-type Doping Technology Of AlGaN-based Materials

AlGaN ternary alloys are the ideal materials for fabricating the optoelectronic devices such as deep ultraviolet light-emitting diodes（DUV-LEDs）because the band gaps of AlGaN-based materials are tunable between 3.4 e V（Ga N）to 6.2 e V（Al N）.In this thesis,firstly,a series of high-quality polar/semi-polar/non-polar AlGaN-based materials were successfully grown on various kinds of sapphire substrates by using metalorganic chemical vapor deposition（MOCVD）technology.Moreover,the detailed and in-depth studies about epitaxial growth and doping technology of non-polar a-plane p-type AlGaN materials were carried out.In addition,a fabricating process for the quasi-ordered nano arrays structure was developed.Furthermore,the effect of the quasi-ordered nano arrays structure on the optical properties of semi-polar（112 2）plane AlGaN-based multiple quantum wells（MQWs）was systematically studied.The major works conducted in this research are listed as follows:The non-polar a-plane p-AlGaN epi-layers were successfully grown on r-plane sapphire substrates with Mg-delta-doping technique.A hole concentration of 3.7×10¹⁷ cm^-3 and an electrical resistivity of 2.6Ω?cm were achieved by carefully optimizing theⅤ/III ratio and Cp2Mg flow rate during the epitaxial procedure.A novel MOCVD growth process featured with pulsed mass flow supply（PMFS）of the metal organic-source was applied for the preparation of the Mg-doped AlGaN epi-layer with high Al composition.On the one hand,a stable N-rich atmosphere could be formed during the growth of the p-AlGaN epi-layers with the introduction of the PMFS technique.Therefore,a significant enhancement in electrical conductivity was obtained due to the decrease in the density of the nitrogen vacancy（VN）.On the other hand,by using the newly-developed PMFS technique the diffusion length of Ga and Al adatoms could be effectively extended.Therefore,the crystalline quality and the surface morphology of the p-AlGaN epi-layers could be significantly improved owing to the application of the newly-developed PMFS technique during the MOCVD growth process.In fact,a hole concentration of 2.3×10¹⁶ cm^-3,a hole mobility of 4.6 cm²/V?s,and an electrical resistivity of 36.3Ω?cm were achieved for the p-Al0.53Ga0.47N sample.The nonpolar a-plane p-Al0.6Ga0.4N/Ga N superlattices（SLs）were successfully grown by using indium（In）-surfactant during the MOCVD growth process.On the one hand,the enhancement in the electrical conduction was achieved due to the improvement in the incorporation efficiency of Mg atoms and the suppression of the formation of the VN.On the other hand,the evident improvement in the surface morphology and the crystalline quality could be ascribed to the prolonged Al or Ga adatom diffusion length with the introduction of In-surfactant.In fact,a RMS value of 0.8 nm,a hole concentration of 5.1×10¹⁷ cm^-3,and a hole mobility of 4.7 cm²/V?s were achieved for the nonpolar a-plane p-Al0.6Ga0.4N/Ga N SLs.Quasi-ordered nanorod（NR）arrays structure was successfully developed by means of self-assembly technique using polystyrene spheres formed on a 2-inch sapphire substrate.Moreover,the quasi-ordered semi-polar（112 2）plane MQW NR arrays with the emitting wavelength of266 nm were fabricated.The PL integral intensity of the MQW NR arrays was enhanced by 1.5times compared to that of the conventional planar MQWs.Moreover,the degree of polarization was increased from 15.9%for the planar MQWs to 26.2%for the MQW NR arrays due to the modified light extraction of the quasi-ordered NR arrays.