Phosphorus Diffusion in Amorphous Silicon

Abstract

The properties of amorphous silicon (a-Si)a promising material for semiconductor electronicshave become intensively investigated. One of the most important probl'ems is doping of a-Si. In this connection, a study of diffusion of the main electrically active impurities into amorphous silicon appears to be an urgent problem.The present note deals with phosphorus diffusion into a-Si, produced by ion-plasma sputtering. Sputtering of the silicon target was carried out in an argon plasma at 9 x 1 0~~ Torr. Before bleeding-in of argon the vacuum system was evacuated up to 8~1 0 -~ Torr. The distance between the sputtered silicon plate and the substrate was 12 cm. A plate of p-silicon with a resistivity of 2000 Qcm was used a s substrate, the temperature of which was kept at 100 OC. The film thickness of a-Si was about 2000 8 . The structure of the sputtered semiconductor layer was controlled by electron diffraction. The diffusion was performed in evacuated quartz ampoules in the temperature range of 310 t o 520 OC from a sample of red phosphorus. Measurement of the impurity distribution was carried out by Auger spectroscopy together with argon ion beam etching.The regions with the precipitations of pure phosphorus were located in the diffusion layer. The distribution of the diffused phosphorus was analysed in the regions free of these precipitations. In Fig. 1 the dependence of phosphorus atom concentration on the de#h is shown. The experimental curves for the low temperature region (31 0 to 350 O C ) may be satisfactorily approximated by an erfc function. This allows the diffusion process t o be considered as controlled by a single mechanism with a constant diffusion coefficient. ' 1) ul. Gagarina 23, 603600 Gorkii, USSR.

Crystalline Silicon Solar Cells with Thin Silicon Passivation Film Deposited prior to Phosphorous Diffusion

“…This can be explained as follows. Diffusion of phosphorus at a high temperature in a-Si was carried out by migration through a large number of vacancies in a-Si in a high-temperature environment [27]. The activation energy of the phosphorus diffusion in a-Si is lower than that in sc-Si.…”