Effects Of Substrate Pretreatments On The Quality Of Gallium Nitride Epilayers

In this paper, the GaN layers and AlGaN/GaN 2DEG were prepared by Radio Frequency Molecular Beam Epitaxy(RF-MBE) on the sapphire and silicon which were pretreated. The thin films on different substrates were characterized.The chemical etching experiments were processed on sapphire substrate at different temperatures for different times by using fused KOH etchant. It is found that the preferable condition for dislocation displaying is etching 15 min or 25 min at 290℃. when the etch time is 15 min at different temperatures, the size of etch pits will be increasing, and there will be a peak for the density of the etch pits; the morphology of etch pits are changed from the triangle to the polygon. And the mechanisms were analyzed by further analysis, there are three increasing ways about the etch pits. The etch pits annex each other; merger between the close pits; the expansion of outer edge of etch pits.At low temperature conditions, GaN epitaxial films were deposited by the use of ZnO as a buffer layer on sapphire and silicon substrates. After hydrochloric acid treatment, it is found that they have good properties of luminescence by PL analysis; epitaxial GaN films which were deposited on sapphire substrates by RF-MBE under normal conditions were investigated. It is found that the films which are obtained under Ga-rich and nitrogen-rich conditions are better than the ones which are obtained under nitrogen-rich conditions in terms of crystal quality, the morphology of surface, optical properties, electrical properties, etc; the GaN thin films were studied which the buffer layer were grown for 20 min and 30 min separately under Ga-rich conditions. It is found that the buffer layer which are thicker can get a better crystal quality, the morphology of surface on flatness and roughness, the stress of epitaxial layer and electrical properties will be improved.In the paper, AlGaN/GaN and the mechanism of formation were both studied. The 2DEG has good crystal quality, optical properties, etc. The electron mobility at room-temperature is 800 cm2/(V·s); The sheet electron concentration is 1.14×1013 cm-2 through theoretical calculations which is closed to the experimental data; Through theoretical calculations, the value of spontaneous polarization is -0.04444 C/m2 and the piezoelectric polarization is -0.0078 C/m2.