Influence of heterogeneities on the electronic properties of hydrogenated amorphous silicon

Abstract

An attempt is made to highlight the importance of inhomogeneities in hydrogenated amorphous silicon (a-Si:H), in controlling its electronic properties. We note that hydrogen increases the gap in a-Si:H and that hydrogen is distributed inhomogeneously in it. This gives rise to long-range potential fluctuations, which are mostly uncorrelated and usually ignored. These and other such considerations have not only enabled us to gain new insights into the behaviour of a-Si:H in general, but have also allowed us to resolve several unsolved puzzles. Among these are questions like why undoped a-Si:H is n-type, why the creation of dangling bonds upon light soaking (LS) so inefficient, why a-Si:H degrades more upon LS when it is doped, why the reciprocity fails for light-induced degradation, why presence of nanocrystalline silicon improves stability and so on. We provide evidence to support some of our ideas and make suggestions for verifying the others.

Femtosecond Laser Fabrication of Anisotropic Structures in Phosphorus- and Boron-Doped Amorphous Silicon Films

“…The concentrations of the main charge carriers n e,h in the films—electrons in n-a-Si and holes in p-a-Si—are close in magnitude: n e ≈ 10 14 cm −3 and n h ≈ 3 × 10 13 cm −3 , estimated according to the formulae n e = σ n, /eμ De , n h = σ p /eμ Dh , where σ n,p is the specific conductivity of the initial n- and p-type films from Table 3 , respectively, and e is the elementary electric charge. Undoped a-Si has weak properties of an n-type semiconductor [ 49 , 50 ], whereas p-type doping converts it to compensated semiconductor. Crystallization caused by the laser treatment activates both p- and n-type impurities [ 51 ].…”