Atomic and electronic structure of amorphous and nanocrystalline layers of semi-insulating silicon produced by chemical-vapor deposition at low pressures

Abstract

Semi-insulating silicon SIPOS layers are prepared on single-crystal silicon substrates of two orientations Si (111) and Si (100) by chemical-vapor deposition at a reduced pressure in a horizontal hot-wall reactor at a temperature of 638°C and pressure of P = 20 Pa with a silane flow rate of 8 L/h and the addition of nitrous oxide into the reactor environment. Electronic-structure and phase-composition investigations by ultrasoft X-ray emission spectroscopy (USXES) and X-ray diffraction (XRD) methods show that the addition of nitrous-oxide gas into the reactor environment results in the formation of amorphous silicon layers. The layer-by-layer-phase analysis via USXES of the SIPOS samples to a depth of 120 nm without destruction indicates the predominance of oxide phases in the sample surface layers with a thickness of about 10 nm. The general content of unbound and bound oxygen of less than about 10%, below which nanocrystalline silicon is formed with an average particle size of 60–70 nm, can be considered as some conditional crystallization threshold of SIPOS amorphous layers.