Grain Growth and Mobility in Nanocrystalline Ge Films

Abstract

In this paper, we report on deposition and properties of nanocrystalline Ge:H films . The films were grown from germane and hydrogen mixtures using Radio frequency Plasma-enhanced chemical vapor deposition (RF-PECVD) process using ~45 MHz frequency. The crystallinity of the films was measured using Raman measurements and from x-ray diffraction techniques, it was found that the grain size was a strong function of deposition pressure, temperature and hydrogen/germane ratios. High hydrogen ratios and high powers led to films with smaller grains. Higher pressures and smaller hydrogen/germane ratio led to films with larger grain sizes, as did higher growth temperatures. The mobility of electrons and holes was measured using space charge limited current (SCLC) techniques in n + -n-n + devices. It was found that nominally undoped films were generally n type with carrier concentrations in the 1E14/cm 3 range. Mobility was found to increase with grain size, with 60 nm grains showing mobility in the 2-3 cm 2 /V-s range.