Wide band gap amorphous silicon thin films prepared by chemical annealing

Abstract

High quality wide gap hydrogenated amorphous silicon films were prepared using a hydrogen chemical annealing technique involving the deposition of thin amorphous silicon films followed by a hydrogen radical (and/or ion) treatment. Thick films were prepared by repeating this process many times. The substrate temperature and the hydrogen treatment time can be used to select optical band gaps ranging from 1.8 to 2.1 eV. Low dangling bond defect densities in the as-deposited films ranging from 3 to 8×1015 cm−3 were measured over the entire optical band gap range. The light induced dangling bond densities were less than those found in standard high quality amorphous silicon. The optical band gap is strongly correlated to the medium range structure characterized by the dihydride density. The electronic transport and stability are correlated with the Si–Si bonding environments and the associated short range order including bond angle and bond length distributions.

From amorphous to microcrystalline silicon: Moving from one to the other by halogenated silicon plasma chemistry

“…During these processes, the effective etching of weakly adsorbed bonds by hydrogen and fluorine atoms can establish the crystalline structure. Although various mechanisms have been proposed to contribute to the amorphous-to-microcrystalline transition [65,72,73], the fluorine-atoms etching contributes mainly to the nano-and micro-crystallinity in SiF 4 -based plasmas [74]. We have previously demonstrated a semi-quantitative correlation between the film crystallinity and the deposition/etching competition [38], which is sketched in Fig.…”

“…Noteworthy, also the a-Si:H:F film deposited from SiF 4 -H 2 in our labs shows ε 2 at its peak ∼30 although with a higher optical gap due to the fluorine inclusion. It is well known that to promote the amorphous-to-microcrystalline phase transition during the PECVD of silicon from SiH 4 -H 2 , hydrogen dilution plays an important role [73,79,80].…”

Nucleation mechanism of microcrystalline silicon from the amorphous phase

“…The importance of H in lc-Si:H nucleation is well recognized, as crystallization hardly takes place at lowtemperatures using pure SiH 4 . To explain H-induced lcSi:H formation, several models have been proposed [1][2][3][4][5]. Nevertheless, the role of H in the lc-Si:H nucleation process remains controversial among these models.…”

“…The phenomenon of microcrystalline silicon (lc-Si:H) nucleation from the hydrogenated amorphous silicon (a-Si:H) phase has been observed at low-temperatures (50-450°C) using several thin-film deposition techniques including plasma-enhanced chemical vapor deposition (PECVD) [1][2][3][4][5][6][7][8], reactive magnetron sputtering [9], and catalytic chemical vapor deposition [10]. Nucleation of lcSi:H is most commonly observed in thin-film deposition using SiH 4 as the source gas, diluted by a large quantity of H 2 .…”

Effects of hydrogen pressure on hydrogenated amorphous silicon thin films prepared by low‐temperature reactive pulsed laser deposition

“…Hydrogenated amorphous silicon (a-Si:H) thin-films are being developed by several methods, including plasma-enhanced chemical vapor deposition [1,2,3], hotwire chemical vapor deposition [4,5], sputtering [6,7,8], chemical annealing [9], and reactive pulsed laser deposition (PLD) [10,11,12,13], among others, resulting in various optical and electrical properties, film qualities and uniformities, and deposition rates. Reactive pulsed laser deposition allows for the development of hydrogenated silicon thin films via laser ablation of a silicon target in a hydrogen atmosphere.…”