0 Pressure Dependence of the Barrier Height in Tunnel n - GaAs / Au Junctions

The theory of tunnel current-voltage (I-V) characteristics of metal-semiconductor junctions based on the self-consistent solution of Poisson equation allows to get the Schottky-barrier height and the charged impurity concentration directly from the tunnel-ing data. This approach was applied to the analysis of the low temperature experiments on tunneling under pressure up to 3 GPa in a piston-cylinder gauge. Here we present the barrier height versus pressure for heavily doped n-GaAs(T e)/Au (N e ∼ 5 − 7 · 10 18 cm −3) tunnel junctions and compare the obtained pressure dependence of the Schottky barrier with known behavior of the band gap under pressure taking into account the influence of the Land X-valleys and DX centers. The knowledge of doping level and the potential barrier height at the interface as well as their dependence on pressure is important for studies of the semiconductor structures where the surface band bending region is essential. Our previous works [1, 2] showed that it is possible to carry out qualitative low-temperature tunneling spectroscopy experiments at pressure up to 3 Gpa using stand-alone high-pressure cell. The aim of this work is to extend this technique to quantitative study of band bending region in heavily-doped semiconductors under high pressure. The pinning of the Fermi level that determines the magnitude of Schottky barrier may be attributed to metal-induced gap states [3]. In the particular case of the Au contact to n-GaAs (100) plane the barrier formation was studied by photoemission spectroscopy on N e = 5 · 10 18 cm −3 doped material [4]. The barrier height Φ s = 1 eV was obtained at Au coverage beginning from 1 monolayer. This value coincides with the results obtained in [5] by means of tunneling spectroscopy for the same or less doped case, however, the junctions with higher doping level indicated decreasing the barrier height. Nevertheless, too little is known about the barrier in the case of heavily doped GaAs, especially under pressure exceeding approximately 1.5 GPa, when the electron states related to above lying L-and/or X-minima might overlap with the states in Γ-minimum of the conduction band occupied by the electrons. Obtaining the suitable data experimentally is rather a difficult task in the case of heavily-doped semiconductors, because the free carrier tunneling across the barrier prevents from implementation of the usual techniques like capacitance-voltage (C-V) or barrier photo-e.m.f. measurements [5]. The use of tunneling current itself instead seems …