Photoluminescence and absorption properties of the surface functional layer of CdTe crystals

Dmytro V. Gnatyuk, Leonid V. Poperenko, Iryna V. Yurgelevych, Oleksandr Dacenko, Toru Aoki, and Manato Kimura "Photoluminescence and absorption properties of the surface functional layer of CdTe crystals", Proc. SPIE 8507, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIV, 85071U (24 October 2012); https://doi.org/10.1117/12.940764

Photoluminescence and optical properties of the surface functional layer of detector-grade Cl-compensated semiconductor CdTe(111) single crystals modified by chemical etching and nanosecond laser processing have been studied. A bromine-methanol solution was used for polishing etching and nanosecond pulses of the second harmonic of YAG:Nd laser was applied as a radiation source. The photoluminescence spectra were excited at 80 K by an argon-ion laser with wavelength of 488 nm. The intrinsic emission band at 1.56 eV and broad defect band peaked at 1.45 eV were observed in the spectra before and after chemical and laser processing of CdTe crystals. The emission between 1.4-1.5 eV was associated with carrier recombination at defects in the surface region, so called the band of surface states. The optical parameters were determined using an ellipsometer with laser wavelength of 632.8 nm. Refraction n and absorption k indices were calculated within model of a homogeneous absorbing surface layer upon an absorbing substrate. An increase in n and k was observed at laser irradiation with energy density near or higher than the CdTe melting threshold that was attributed to an increase in volume fraction of Te in the surface region of the crystal. A decrease in the emission intensity at 1.45 eV was evidence of a reduction of the surface impurity contribution to the spectrum as a result of chemical etching. A rise of this band after irradiation was due of formation of point defects and dislocations in a surface layer of the crystal.