Review of Experimental Results

Abstract

The theory of electron transport has been presented in the earlier chapters in all its complexity. The characteristics of important transport phenomena have also been described. We have not, however, considered any detailed experimental results or discussed how far the theory explains the available results. The total number of compound semiconductors is very large. There are about twelve important III-V compounds, six II-VI compounds, three IV-VI compounds and innumerable kinds of mixed and chalcopyrite compounds. It is impossible to discuss the transport properties of all these materials, nor would such coverage be meaningful at this stage, since reproducible data for well-characterised samples are generally not available. The data reported in the literature are mostly obtained by using available samples, which are not often in perfectly crystalline form and may be very impure, with unknown impurity concentration. The samples have been characterised by stating the electron concentration determined from the value of the Hall coefficient by assuming that the Hall factor is unity. This assumption may introduce an error of about 10–20% in the values of the electron concentration. Even if this error is ignored there remains a factor of greater uncertainty. The experimental samples are mostly compensated and the impurity concentration may be radically different from the electron concentration. We find on plotting the transport parameters against electron concentration that the data points are scattered within ranges differing by orders of magnitude.