Characterization of p-Type CdTe Bridgman Crystals by Infrared Extinction Spectra

Abstract

Room-temperature infrared extinction spectra measured on a large number of as-grown p-CdTe crystals are decomposed into three contributions: (i) intra-valence-band absorption, (ii) absorption due to a characteristic impurity center, and (iii) scattering from Te precipitates and/or inclusions. The separation of the scattering contribution is based on calculations yielding power-law dependences on photon energy. Proportionality between the intra-valence-band absorption coefficient and the hole concentration obtained from Hall measurements is observed over nearly four orders of magnitude, giving an absorption cross-section of 2.9 × 10−16 cm2 at λ = 10 μm. The scattering coefficients are found to be correlated with the concentrations of Te particles determined by transimission infrared microscopy. The radial and axial distributions of the hole concentration and of the scattering coefficient within a vertical Bridgman grown boule are determined, and these can be explained on the basis of the growth conditions and the segregation behaviour of point defects.