ELECTRICAL CHARACTERISATION OF SEMICONDUCTOR THIN FILMS ON CONDUCTING SUBSTRATES

摘要

A new characterization technique has been designed for measurements of transversal electricalconductivity of thin semiconductor films on substrates with good electrical conductivity. An example of suchstructure may be absorber layer on the bottom contact of a thin film solar cell. The technique is especially suited forstudies of rough inhomogeneous films, even with shunts. The principle of operation is measurement of highfrequency impedance of the film, being capacitive-coupled to another electrode through a thin liquid layer of highdielectric constant. Absolute measurements of the conductivity are possible, making measurements of minoritycarrier lifetime potentially feasible. The conductivity of the film may be modulated using a periodically modulatedlight source, so that the impedance modulation may be measured lock-in very sensitively. The technique has beenapplied to coevaporated CuInS2 on molybdenum-coated soda lime glass. It was possible to measure the specificconductivity of the film material and to observe its metastability.