PRECIPITATION IN CDTE CRYSTALS STUDIED THROUGH MIE SCATTERING

Below gap optical losses in as-grown n-type CdTe crystals were analyze d in terms of free carrier absorption and Mie extinction due to Te pre cipitates. Experimental absorption spectra measured between 2 to 20 mu m exhibited the well-known free carrier absorption behavior alpha(FCA )similar to lambda(x) with x = 3 due to scattering by polar optical ph onons. In shorter wavelength regions below 6 mu m, however, additional contributions to the light loss due to absorption and scattering by p recipitates were also observed. Assuming a log-normal size distributio n, the precipitate extinction spectra were calculated according to Mie theory within the electric and magnetic dipole and electric quadrupol e approximation. A comparison with the experimental spectra identifies the precipitates and enables estimation of their sizes and total numb er density. In this investigation, both undoped and In-doped CdTe crys tals grown from stoichiometric melts by vertical asymmetric Bridgman m ethod were used. It was found that In doping, in general, suppresses T e precipitation. At high doping level (melt containing similar to 10(1 9) In atoms cm(-3)), the formation of In2Te3 is also indicated. It is demonstrated that the Mie extinction analysis offers an expedient meth od to rapidly analyze the precipitates in CdTe and in similar other wi de gap materials in a nondestructive manner.