Study of the surface state density and potential in MIS diode Schottky using the surface photovoltage method

The effects of surface preparation and illumination on electric parameters of Au/GaN/GaAs Schottky diode were investigated. The thin GaN film is realized by nitridation of GaAs substrates with different thicknesses of GaN layers (0.7 - 2.2 nm). In order to study the electrical characteristics under illumination, we use an He-Ne laser of 632 nm wavelength. The I(V) current-voltage, the surface photovltage SPV measurement were plotted and analysed taking into consideration the influence of charge exchange between a continuum of the surface states and the semiconductor. The barrier height Phi(Bn), the serial resistance R-s and the ideality factor n are respectively equal to 0.66 eV, 1980 Omega, 2.75 under dark and to 0.65 eV, 1160 Omega, 2.74 under illumination for simple 1 (GaN theckness of 0.7 nm). The interface states density N-ss in the gap and the excess of concentration delta(n) are determined by fitting the experimental curves of the surface photovltage SPV with the theoretical ones and are equal to 4.5 x 10(12) eV(-1) cm(-2), 5 x 10(7) cm(-3), respectively, for sample 1 and 3.5 x 10(12) eV(-1) cm(-2), 7 x 10(8) cm(-3) for sample 2 (GaN theckness of 2 nm). The results confirm that the surface photovoltage is an efficient method for optical and electrical characterizations.