Correlation between dislocation etch pits, carrier concentration and optical absorption in CdGeAs2 grown by modified Vertical Bridgman method

Abstract

As a promising material for second harmonic generation (SHG) and optical parametric oscillator (OPO), CdGeAs2 single crystals are difficult to reproducibly grow with low loss optical, particularly in the region of 5.5 μm. In addition, a correlation between processing conditions and absorption has attracted various researchers to focus on this problem. This paper describes a series of etching experiments and Hall measurements which were undertaken to see if there might be a relationship between dislocation density, carrier concentration and optical absorption. In this study, a single crystal was grown by the modified Vertical Bridgman method. The spontaneous nucleation growth direction has been determined as [102]. Etch pit densities (EPD) about 105 cm−2 were observed at the edges of the boules, whereas etch pits were almost not found in the center. The distribution of dislocation along the radial direction affected optical homogeneity, and the high EPD caused the low transmittance. Meanwhile, the samples are p type at room temperature with hole concentrations varying from 1014 to 1016 cm−3. A linear correlation between absorption at 5.5 μm and hole concentration is established. The results of these experiments are very useful for improving radial and axial optical uniformity of the crystal grown by modified Vertical Bridgman method.