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In this work, we report on the effect of temperature on near-surface band bending and surface photovoltage (SPV) in GaN. Band bending and SPV during illumination and after switching the illumination off are calculated for n -type and p -type GaN by using a thermionic model. The temperature and temporal dependencies are compared with experimental data. We find that the thermionic model describes adequately the SPV values and its dynamics only at high temperatures. At temperatures below room temperature the observed SPV is much higher than predicted from the thermionic model, especially in the case of p -type GaN. This fact is explained by a significant shift of the quasi-Fermi level in p -type GaN under illumination. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) from high-quality GaN codoped with silicon and zinc was investigated in detail. The internal quantum efficiency (IQE) of PL was determined from the analysis of the dependencies of the PL intensity on the excitation intensity and temperature, and the simulation of these dependencies with a phenomenological model based on rate equations. The model reproduces an important phenomenon: the quenching of a recombination channel with a high IQE causes a rise in efficiency of all the other PL bands. Quantitative analysis of this phenomenon allows one to determine reliably the absolute IQE of PL. The absolute IQE of the PL in GaN co-doped with Si and Zn exceeds 90%, with the largest contribution coming from the blue luminescence band associated with the ZnGa acceptor. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We have investigated the N- and Ga-polar faces of bulk GaN substrates with photoluminescence (PL) and the surface photovoltage (SPV) technique using a Kelvin probe attached to an optical cryostat. Experiments were conducted in vacuum. Some of the surfaces were mechanically polished (MP), while others were epi-ready after a chemical-mechanical polish (CMP). From the SPV measurements, the band bending in a sample having both surfaces treated with the CMP method was calculated to be about 0.83 and 0.70 eV for the Ga- and N-polar surfaces, respectively. The restoration of the SPV after ceasing the UV illumination showed that the SPV from CMP-treated surfaces behaved as predicted by a thermionic model, whereas the SPV from MP-treated surfaces restored with a much faster-than-predicted rate. This result can be interpreted by the hopping of charge carriers in the highly-defective near-surface layer of the MP-treated samples. Remarkably, removing the top 700 nm defective layer by dry etching restored the quality of the electrical and optical properties of GaN. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]