Annealing Effects on Deuterium in a-Si:D
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ANNEALING EFFECTS ON DEUTERIUM IN a-Si:D.* V. P. Bork,t P. A. Fedders, D. J. Leopold,* and R. E. Norberg, Washington University, St. Louis, Missouri 63130 J. B. Boyce and J. C. Knights, Xerox PARC, Palo Alto, California 94304 ABSTRACT Progressive annealing of a-Si:D and a-Si:DH samples between 250 and 600"C is found to eliminate the broad central deuteron magnetic resonance (DMR) spectral component associated with weakly bonded D. The well-resolved doublet arising from tightly bound D diminishes in intensity. The narrow central line associated with microvoid-contained molecular D2 and HD increases and then decreases for the warmest anneals. DMR relaxation times, line shapes, and hole-burning spectra reflect changes in sample morphology upon annealing. INTRODUCTION Deuteron magnetic resonance (DMR) provides useful structural information about hydrogenated (deuterated) amorphous semiconductors [1]. Tightly bound deuterium (TBD) in a-Si:D gives rise to a well-defined 66 kHz quadrupolar doublet. Weakly bound deuterium (WBD) corresponds to a broad central resonance component whose line width is independent of temperature. A temperature dependent narrow central(NC) line arises from dense molecular deuterium (D 2 and HD) in microvoids. The NC line width reflects motional narrowing of quadrupolar broadening which arises principally from electric field gradients (efg) originating from microvoid silicon surfaces. Spin-lattice relaxation of the NC component reflects close contact with effectively dilute [2] relaxation center para-D 2 adsorbed on microscopically rough void walls. This T1 is characterized by power law temperature variation on either side of a T1 minimum. The present work describes changes in 30 MHz DMR spectra and relaxations which accompany annealing of a-Si:D,H samples. Xerox PARC Samples [11 (here designated as II and V) were plasma-deposited onto aluminum substrates under conditions specified in Table I. The Al substrate then was etched away with dilute HCI. Sample V was prepared from SiD 4 and Ar. Its small H content may have arisen from a hydrogen impurity or from the HCI treatment. Sample II was made from SiH 4 and D2. RESULTS Figure 1 shows 25 K DMR line shapes for the nearly perdeuterated Sample V before and after annealing near 500'C. The anneal has reduced the total D content, eliminated the broad central (WBD) component, and increased the NC molecular deuterium content relative to that of the resolved doublet (TBD). The anneal also has narrowed the NC lin1e by about a factor of two between 14 and 33 K. which is the limited range of T2 data for the unannealed sample. *Supported in part by NSF Grant 85-03083. Xerox Corporation Pre-Doctoral Fellow SPresent Address: McDonnell Douglas Research Labs
Mat. Res. Soc. Symp. Proc. Vol. 70. 5
1986 Materials Research Society
90 Table I Sample Preparation and D Concentrations for a-Si:D,H Before Anneal Sample Gas Mixture (%) Substrate T ('C) 2 RF Power (W/cm ) n(D) (at.%) Resolved Doublet (D) Broad Central (D) Narrow Central (D2)
#II SiH4(5)/D 2(95) 25 0.1 2
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