Roles of hydrogen in structural stability and electronic property of bulk hydrogenated amorphous silicon

Abstract

Hydrogenated amorphous silicon (a-Si:H) has been widely used due to its unique photoelectric properties, but the information about its structure is patchy and the factors that affect its electronic properties are also unclear. In this work, we predicted the bulk a-Si:H structures based on the particle swarm optimization (PSO) technique and explored its structural characteristics under different hydrogen content conditions, then the effect of structural characteristics such as hydrogen content, void size and hydrogen-bonding configuration on structural stability and electronic properties of these structures are revealed. The results indicate that the structures with lower hydrogen content are conductors whereas the structures with higher hydrogen content are semiconductors. The band gaps of bulk a-Si:H structures show a trend with an increase followed a decrease with the increase of hydrogen content, which can be reduced by increasing the void size or adding some Si-H2, Si-H3 or Si-H-Si bonds to structures. The transition-state structure containing Si-H-Si bonds should have better conductivity than the steady-state structures. These results provide comprehensive understanding of the structural characteristics and electronic properties of bulk a-Si:H structures, which provides a theoretical support for the application of a-Si:H in semiconductor devices or as secondarybatteryanodes and have broad implications for further investigating other physical properties of a-Si:H structures.