Growth and Electronic Properties of Nanocrystalline Si

Abstract

Nanocrystalline Silicon is an important electronic materials for solar cells, for display devices and for sensors. In this paper, we discuss the influence of ions on the growth and properties of the nanocrystalline Si:H material. Using a unique growth geometry, combination of hot wire and ECR plasma growth, we show that low energy ion bombardment is beneficial for growing high quality materials. Ion bombardment by H is shown to etch the films during growth and also promote crystallinity. The results of film growth are compared with simulations of growth using the SRIM program. The electronic properties measured include mobilities of both electrons and holes in device-type structures, carrier lifetimes, diffusion lengths, defect densities and capture cross-sections for holes. Electron mobility is found to increase with grain size, with a minimum mobility being in the range of 1 cm 2 /V-s. The hole mobility is also in this range, and three different methods of measuring it give approximately the same value. The capture crosssection for holes is of the order of 1-2 x 10 -16 cm 2 . The lifetime of carriers is found to depend inversely on the defect density, implying that the recombination is trap controlled.

Alternative designs for nanocrystalline silicon solar cells

“…The deposition pressure used is 100mT. The reason behind this is explained by previous work done in our group [119,120,121].The standard operating temperature is 275C. The constituent gases are Silane and Hydrogen(SiH 4…”

Study of electronic characteristics of heterojunction with intrinsic thin-layer devices and defect density profile of nanocrystalline silicon germanium devices

“…Next, a thin layer of a-Si lightly doped with PH3 is deposited to act as the seed layer for the nc-Si, which is gradually graded to nc-SiGe with the desired germanium content. The seed layer functions to provide nucleation sites and prevent phosphorous from diffusing into the main intrinsic layer [57]. A high hydrogen dilution is initially used to aid in formation of the nucleation centers and jumpstart the onset of crystallization.…”