The surface chemistry and electrical properties of p-type and n-type AlGaN surfaces were studied via x-ray photoelectron spectroscopy before and after oxidation and wet chemical treatments. Shifts in the surface Fermi level were measured with the change in onset of the valence-band spectra. Oxidation and HF and (NH4)2Sx treatments on p-type AlGaN (n-type AlGaN) led to an increase (the reduction) in the surface band bending due to more N vacancies and N vacancies being occupied by S (i.e., donorlike states) than Al vacancies and Ga vacancies (i.e., acceptorlike states) near the p-type AlGaN (n-type AlGaN) surface region. The changes in surface chemistry indicate that oxidation and wet chemical treatments alter the surface state density through the formation of more donorlike states.
The influence of the thickness of p-type InGaN (p-InGaN) capping layers grown on p-type GaN (p-GaN) on the electrical properties of Ni contacts on p-GaN was investigated in this study. Experiments and simulations indicated that a thicker p-InGaN capping layer grown on p-GaN led to the formation of a higher concentration of a two-dimensional hole gas (2DHG) at the interfaces. In addition, owing to a low barrier at the interfaces, holes can be easily injected into the p-GaN layer through recessed channels and a 2DHG channel, resulting in the formation of nonalloyed ohmic contacts with a low specific contact resistance of 1.7×10-5 Ω cm2.
The effect of the damage caused by reactive ion etching on the optical properties of heavily Mg-doped p-type GaN (p-GaN) was investigated in this study. After etching, we found that the blue luminescence (BL) is redshifted and the intensity of the redshifted BL is markedly increased at room temperature, which are attributed to the formation of the lattice disorder resulting in the domination of distant donor-acceptor pairs (DAPs) and the formation of more nitrogen-vacancy-related defects resulting in more recombination centers D responsible for DAP transition.
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