MOCVD Growth And Characterization Of Non-polar N-AlGaN Materials

As one of the third-generation semiconductor materials,Al Ga N-based materials have a very broad application prospect in the field of optoelectronic devices such as deep ultraviolet light emitting diodes(DUV-LEDs).Theoretically,the DUV-LED fabricated with non-polar Al Ga N material in which the so-called quantum-confined Stark effect(QCSE)could be completely suppressed along the growth direction should have higher emission efficiency than that for the conventional polar Al Ga N-based DUV-LED.In this thesis,metal-organic chemical vapor deposition(MOCVD)technology is used to grow the Si-doped n-type non-polar(112 ?0)a-plane Al Ga N materials.After the optimization of the pulsed-flow method,V/III ratio,and the Si H4 molar flow rate in the epitaxial growth process,the non-polar(112 ?0)a-plane n-type Al Ga N epi-layer with high Al composition and high electron concentration was successfully grown on(112 ?0)r-plane semi-polar sapphire substrate.The major works conducted and results achieved in this research are listed as follows:1.Based on the two-step pulsed-flow growth method,the V/III ratio in the epitaxial growth process for the non-polar Al Ga N materials was optimized.High-resolution X-ray diffraction(HR-XRD),atomic force microscope(AFM),and ultraviolet-visible spectrophotometry(UVVis)were used to examine the influence of NH3 flow rate on the crystalline quality and surface morphology of the non-polar a-plane n-Al Ga N epi-layer,respectively.2.Three different pulsed-flow growth methods had been used for the growth of the Sidoped non-polar n-Al Ga N epi-layers,and the impact of the growth method on the efficiency of the n-type doping for the non-polar n-Al Ga N materials was investigated.The key factors and difficulties in the doping progress had been analyzed and clarified.The research results show that the metal-pulsed growth method helps to promote the incorporation of Si element during the epitaxial growth of Si-doped non-polar n-Al Ga N materials with high Al composition.Moreover,it was found that with the optimization of the V/III ratio during the epitaxial growth process the doping level of the non-polar n-Al Ga N materials could be further improved.3.The effect of SiH4 mole flow rate on the electrical properties,crystal quality,and surface morphology of the non-polar(112 ?0)a-plane n-Al Ga N epitaxial films grown with MOCVD technology was systematically studied.The behavior mechanism for the Si atoms doped inside the non-polar n-Al Ga N crystal was discussed in detail.The research results show that the electron concentration and electron mobility of the non-polar(112 ?0)a-plane n-Al Ga N materials could be significantly improved by optimizing the Si H4 molar flow rate during the epitaxial growth,while the crystalline quality of the non-polar n-Al Ga N materials could be improved as well to a certain extent.