Low-temperature PECVD deposition of highly conductive microcrystalline silicon thin films

Abstract

In this paper, we present the characterization results of doped n-type microcrystalline hydrogenated-silicon (μc-Si : H) films deposited in a plasma-enhanced chemical vapor deposition in the temperature range between 70 and 250 °C. The interest in these films arises from the fact that they combine the high optical absorption of amorphous silicon with the electronic behavior of the crystalline silicon, making them interesting for the production of large electronic devices such as solar cells, image sensors, and flat panels. It is shown that n-type μc-Si : H films with high electrical conductivity can be obtained even at low temperature deposition, around 120 °C (σ=2.9 S cm⁻¹). The structural properties of the films have been studied by Raman and infrared spectroscopy that allowed for the determination of the crystalline fraction. Electrical measurements were performed by a.c. impedance spectroscopy, Hall effect, and dark conductivity. Characteristics suitable for application in electronic devices were obtained with the developed deposition parameters set-up; the best dark conductivity values were around 1 S cm⁻¹ for deposition temperatures within the 120–140 °C range. Some conclusions regarding the correlation between electrical and structural properties are presented for the considered temperature range.