Effect of electron-hole recombination processes on semiconductor reflectivity modulation

The increases in the reflectivity of germanium, silicon, GaAs, GaSb, In As, InSb, CdTe and CdSe have been observed by use of a ruby laser to produce the electron-hole plasma that is responsible for the reflectivity changes and to probe the reflectivity changes. Observations were made with the ruby laser light incident at the pseudo-Brewster angle in order to measure small increases in reflectivity. In the case of the III-V and II-VI semiconductors, the increase in reflectivity was found to exhibit a linear dependence when plotted as a function of the square root of the incident light intensity. Germanium and silicon exhibited a linear dependence of the increase in reflectivity on the incident light intensity. These results agree with the calculated dependence that ascribes the differences between the two groups of semi-conductors to the fact that the recombination of electrons and holes is a direct process in the III-V and II-VI compounds and in germanium and silicon occurs mainly by trapping of the free carriers at impurity centres.