Nucleation in Amorphous Si:H Alloy
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NUCLEATION IN AMORPHOUS Si:H ALLOY Y.C.Koo*, A.R.Perrin*, K.T.Aust* and S.Zukotynski** *University of Toronto, Dept. of Metallurgy and Materials Science "**University of Toronto, Dept. of Electrical Engineering, Toronto, Ont. Canada, M5S 1A4 ABSTRACT
A method of producing microcrystalline material from thin films of hydrogenated amorphous silicon was investigated. Exposure to gamma and neutron radiation, and silicon self ion implantation were used to induce nucleation in the amorphous material. According to the preliminary results, neutron irradiation represents a most promising method for promoting crystallization. INTRODUCTION AND TERMINOLOGY The microcrystalline phase of hydrogenated silicon (Wsc-Si:H) can be thought of as "an intermediate range order material between crystalline and amorphous silicon (a-Si:H)"[l]. It has recently drawn interest as a new phase material for applications in optoelectronics [2-51. The following sections of the paper describe the experimental work that was done to induce the transition of hydrogenated silicon from the anlorphous state into a microcrystalline material. Exposure of the amorphous material to gamma radiation, neutron bombardment, and silicon self ion implantation were used to induce the phase transformation. The literature review and full experimental details have been reported elsewhere [6,7]. The following a-Si:H g.tc-Si:H ltc,a 7,n° EELS EDX
terminology has been used in this paper for the sake of brevity. refers to hydrogenated amorphous silicon refers to the microcrystalline phase of hydrogenated silicon means microcrystalline and amorphous respectively refer to gamma radiation and neutron respectively is electron energy loss spectroscopy is energy dispersion x-ray micro-analysis.
EXPERIMENTAL PROCEDURE
The three processing stages that were used to produce the gtc-phase in a-Si:H films are listed below. 1. High hydrogen content a-Si:H films were produced in a capacitively coupled RF glow discharge reactor using a SiH 4 /H2 gas mixture. The a-Si:H film deposition conditions are summarized in Table I. Films were deposited on both soda glass and high purity fused quartz substrates. The glass substrates were manufactured by Fisher Scientific Co. (12-542B, 12-548B) and the fused quartz substrates were supplied by Applied Physics Specialities Co.. The chemical composition of the glass and quartz as determined by neutron activation analysis are listed in Table II. The substrates were cleaned by using standard procedures. Over-night baking in a vacuum (pressure less than 2.0x10-4 mTorr) at the deposition temperature of 250'C was used to eliminate residual surface contamination. A mass spectrometer was used to ensure that residual gas impurities were at low concentration levels in the chamber before the deposition took place. The thickness of the films was 1000±100A as determined using the sputter profilling method. N15 hydrogen profiling Mat.Res. Soc. Symp. Proc. Vol.100. 01988 Materials Research Society
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showed that the hydrogen content of the films was about 25
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