Volodymyr Gnatyuk
National Academy of Sciences of Ukraine, Ukraine
Title: Modification of structure and properties of surface layers of semiconductors by nanosecond laser irradiation
Biography
Biography: Volodymyr Gnatyuk
Abstract
Pulsed laser processing of semiconductors with strongly absorbed light has been used for surface cleaning, oxide removal, annealing of structural imperfections, doping, formation of homo/hetero-interfaces, epitaxial recrystallization, etching of material, stress relieving, etc. We have investigated the effect of nanosecond laser pulses on photoelectric and electrical properties of semiconductors which have been used as materials for radiation sensors: GaAs, InSb and CdHgTe for infrared and CdTe, CdZnTe and CdMnTe for X/gamma-ray detectors, respectively. These properties of semiconductors are governed by the intrinsic point defect system (interstitials and vacancies) and extended defects. Application of short pulses of a ruby (694 nm, 20 ns) or YAG:Nd (532 nm, 7 ns) laser made it possible to reduce the thermal diffusion length and hence, to modify the defect structure only in the surface region of crystals and thus, to form micro- and nanolayers with desired parameters. The photoconductivity (PC) spectra and electrical characteristics of the semiconductors were studied before and after laser action. Irradiation with certain energy densities increased the photosensitivity and transformed the PC spectrum profile, in particular the short-wavelength wing rose, then the maximum and long-wavelength edge were shifted toward shorter wavelengths. This was attributed to a decrease of the surface recombination velocity and formation of a layer with wider bandgap, respectively. Irradiation of semi-insulating CdTe pre-coated with an In film resulted in heavy doping of a surface layer of crystals. The laser-based techniques of modification of semiconductor properties have been employed to form the sensor structures for infrared and X/gamma-ray radiations.