Electronic Properties of Hot-Wire Deposited Nanocrystalline Silicon

Abstract

We compare the electronic properties of nanocrystalline silicon from hot-wire chemical vapor deposition in a high-vacuum and an ultra-high-vacuum deposition system, employing W and Ta as filament material. From the constant photocurrent method we identify a band gap around 1.15 eV while, in contrast, a Tauc plot from optical transmission data guides to a wide band gap above 1.9 eV. The sudden change-over from nanocrystalline to amorphous structure in a hydrogen dilution series is also find in the dark and photoconductivity measurements. The samples show a metastability effect in the dark conductivity upon annealing in vacuum with an increase in the dark conductivity, with the large dark conductivity decreasing slowly after the annealing cycle when the cryostat is flushed with air. We identify larger values for the mobility-lifetime products, which corresponds to the smaller defect density shoulder in constant photocur- rent spectra, for the ultra-high-vacuum deposited material compared to the high-vacuun counterpart.

Metastable dark and photoconductive properties of microcrystalline silicon

“…Similar results were also reported for microcrystalline silicon (lc-Si:H) for which heat treatment in vacuum to remove adsorbates has been shown to result in changes in r d [2][3][4][5][6][7][8]. For lc-Si:H both increase and decrease in the room-temperature r d upon heat treatment have been reported.…”

Stability of microcrystalline silicon for thin film solar cell applications

“…There have only been a few investigations on recently prepared material [16][17][18][19][20]. In the present paper we will discuss the results of some of the phenomena for material and solar cells prepared by PECVD or HWCVD and compare these results with earlier investigations.…”

Aging effects in microcrystalline silicon films studied by transient photoconductivity

“…Of the components of room air, it has been suggested that water vapor may be responsible for conductivity increases [1], and oxygen for conductivity decreases [2]. There is continuing interest in the effects of atmospheric aging in lc-Si:H films prepared for photovoltaic applications [4][5][6]. Correlations of changes in conductivity, spin density and infrared absorption on aging with film structure and morphology have recently been reported [4].…”