Influence of Electron Irradiation and Annealing on the IR Absorption of Germanium Single Crystals

In this article, the influence of electron irradiation and isothermal annealing on the transformation of the IR absorption spectra of germanium single crystals doped with an impurity of antimony was studied. The investigated germanium single crystals were irradiated by the fast electrons with the energy of 10 MeV and flow Ω=5·1015el./cm2. Isothermal annealing of the irradiated samples at the temperature of t=120 °C with the step of 1 hour was performed. It was established based on the measurements of infrared Fourier spectroscopy and Hall effect that the main radiation defects, which are responsible for the electrical and optical properties of irradiated germanium single crystals before and after annealing are A-centres modified by two interstitial germanium atoms (VOiI2Ge complexes) and regions of disordering. It is shown that A-centre can be in different charge states (double negative and single negative) depending on the ambient temperature and annealing time. It follows from the solutions of the equations of electroneutrality and measurements of the Hall constant sign for irradiated n-Ge samples that increasing annealing time from 1 to 4 hours leads to the accumulation of A-centres in their volume and n-p conversion of the conductivity type. With further annealing, the concentration of A-centres decreases, and p-Ge is converted back to n-type. The obtained features of annealing kinetics are related to the simultaneous action of two mechanisms: annealing of the primary A-centres formed during irradiation and its second-generation due to annealing of the kernels of regions of disordering. Such anomalous annealing, in turn, affects both quantitatively and qualitatively the IR absorption spectra of n-Ge single crystals. In particular, the intensity of the absorption band of 669 cm-1, which corresponds to the negatively charged state of the A-center, will increase with increasing annealing time to 4 hours and reach its maximum. In the region of intrinsic transitions will be arising the near-edge absorption, which is due to the regions of disordering. The targeted effect of electron irradiation and annealing will provide to obtain based on germanium single crystals the sensitive elements for uncooled infrared radiation detectors, which will be able to simultaneous recording radiation in the region of germanium intrinsic absorption and photosensitivity of negatively charged A-centres.