A Study of Carrier Injecting Properties of Emitter Contacts and Light Spots at Normal and Moderately Elevated Temperatures

The method of determining the injection efficiency γ of an emitter contact (described previously by Shockley, Pearson and Haynes) is discussed and some of the difficulties of the method and the interpretation of experimental results are described. The effects of a fine spot of white light when used as an emitter and hence as a conductivity modulator are investigated and an equivalent minority carrier current for a given optical assembly can be determined. This procedure suggests an experimental method for the determination of γ as a function of temperature. A simple theory for γ in terms of forbidden energy gap, depth of Fermi level, and barrier height ϕ is given and applied to the determination of barrier heights at room temperature, at elevated temperatures, and when an emitter contact on germanium is illuminated. Theoretical curves relating γ and ϕ are presented for Ge and Si of various impurity concentrations. The experiments carried out at elevated temperatures suggest that the surface states on germanium lie at the top of the filled band and that their density is of order 10 10 -10 11 cm -2 .