RF power dependence of the properties of n-type nanocrystalline silicon films deposited by a low-frequency inductively coupled plasma

Abstract

Nanocrystalline n-type silicon films are deposited by a low-frequency inductively coupled plasma at a low H2 dilution, low working pressure of 2.0 Pa and low substrate temperature of 150 °C. The radio frequency (RF) power is set in the range 1000–1800 W. The RF power dependence of the structural, optical and electrical properties of the films is systematically studied. The x-ray diffraction patterns of the films present a (1 1 1)-preferred orientation when the RF power is increased from 1000 to 1800 W. The crystalline volume fraction of the films changes from 51% to 82% while the deposition rate of the films increases from 21 to 36 nm min−1. The UV–VIS spectra show that the optical band gap is in the range 1.4–1.6 eV. Two characteristic hydrogen-related modes located at ∼630 and ∼2100 cm−1 are observed. The carrier concentration of the films ranges from 0.9 × 1019 to 1.1 × 1020 cm−3 depending on the applied RF power. When the RF power is increased, the electron density is increased and the Debye length is decreased while the electron temperature remains nearly constant. The doping mechanism of the present n-type nanocrystalline silicon films is revealed.