Factors Influencing the Quality of a-Si:H Films Deposited by the “HOT WIRE” Technique

Abstract

Device quality a-Si:H has been deposited at 3 Å/s using the “hot wire” technique with 1% SiH4 in He as a source gas. To achieve this deposition rate despite the high dilution, the filament was positioned at 1–2 cm from the substrate. This short distance introduces a large non-uniformity across the substrate in the deposition rate as well as in the film properties. This experimental fact was used to analyze which factors in the deposition determine film quality. We find that radiation from the filament is not an important factor. Data taken from samples deposited at various distances, pressures and flows suggest that the film quality is influenced by radical reactions with SiH4. However, this assumption alone predicts too strong a pressure dependence. The influence of deposition rate as an additional factor can explain the results.

Mechanisms influencing “hot-wire” deposition of hydrogenated amorphous silicon

“…Defining A i as the area under peak i, we report RϭA 2090 /(A 2090 ϩA 2000 ) or RЈϭA 2090 /A 2000 , where increasing R or RЈ corresponds to decreasing film quality. 10,12 One demonstration of this relationship is shown in Fig. 2, where R is plotted versus ph / d , the light to dark conductivity ratio, for a variety of HW-deposited films.…”

“…We have already reported one such study, carried out using silane highly diluted in He and Ar. 10,11 This identified two key processes within the deposition chemistry that determine film quality. In essence, Si atoms reaching the substrate at low P s and radical-radical reactions occurring at high P s are both deleterious to the films.…”

Identifying Electronic Properties Relevant to Improving Stability in a-Si:H-Based Cells and Overall Performance in a-Si,Ge:H-Based Cells; final Subcontract Report, 18 April 1994-15 January 1998

“…[3,37,38] We characterized the electronic properties of a series of NREL deposited hot-wire a-Si:H using transient photocapacitance spectroscopy and also by drive-level capacitance profiling. A comparison of the transient photocapacitance spectra for three hot-wire samples with very different hydrogen levels is displayed in Fig.…”

Identifying electronic properties relevant to improving stability in a-Si:H-based cells and overall performance in a-Si,Ge:H-based cells. Annual subcontract report, 18 April 1995--17 April 1996

“…[2,17,18] We characterized the electronic properties of NREL deposited hot-wire a-Si:H using transient photocapacitance spectroscopy and also by drive-level capacitance profiling. A comparison of the transient photocapacitance spectra for three hot-wire samples with very different hydrogen levels is displayed in Fig.…”