The phenomenon of light-induced excess conductivity (LEC) which occurs in a-Si:H npnp doping-modulated multilayers is found experimentally to be dependent on several different factors. The concentrations of the dopants in n-type and p-type layers affect the Fermi level position, the height of the barriers, and also the density of defects. These parameters are altered by different choices of inert gas diluent (Ar or He) and substrate temperature Ts. For a given set of deposition conditions, the LEC effect can be maximized by varying the layer thickness. With undiluted silane at Ts = 250 °C, the effect was relatively small, reaching a maximum in relatively thick layers (540 Å). The largest effects were obtained for films deposited from silane diluted in helium, using thinner (330 Å) layers. However, for films deposited from silane diluted in argon, the magnitude of the effect and optimum layer thickness was intermediate (440 Å). When Ts was varied, a minimum in LEC was found near 200–250° C. The influence of internal field was examined by using nini, pipi and npnp multilayers. The internal field is a necessary factor to observe a large LEC effect. A compensated film shows a small LEC effect.
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Su, FC., Levine, S. & Vanier, P.E. Parameters Affecting Light-Induced Excess Conductivity in Amorphous Silicon Doping-Modulated Multilayers. MRS Online Proceedings Library 70, 447–452 (1986). https://doi.org/10.1557/PROC-70-447