A DLTS study of the effects of boron counterdoping on the gap states in n-type hydrogenated amorphous silicon

The technique of Deep Level Transient Spectroscopy (DLTS) and related space charge measurement techniques have been applied to a series of 300 vppm phosphine (PH₃) doped, 0–44 vppm diborane (B₂H₆) counterdoped samples of hydrogenated amorphous silicon (a-Si:H). The trends in the resulting density of states, g(E), show: (1) A large increase of g(E) at ≈0.4 to 0.6 eV from the valence band, comparable in magnitude to the total number of B atoms introduced; (2) A smaller decrease in the midgap dangling bond states on the order of ≈2.5% of the added B; (3) A drop in the number of occupied shallow states ≈0.5%; and (4) A quantitative assessment of the degree of autocompensation which shows roughly five compensating midgap states removed for every six shallow acceptor states introduced by B.