Elza Khutsishvili
Ferdinand Tavadze Institute of Metallurgy and Materials Science, Georgia
Title: Peculiarities of absorption near the edge of the fundamental band of irradiated InAs-InP solid solutions
Biography
Biography: Elza Khutsishvili
Abstract
There have been studied the dependence of the optical absorption coef¬ficient (k) vs photon energy (hν) in the long wavelength area of fundamental absorption edge for InP, InAs and InAs-InP solid solutions crystals before and after irradiation by electrons and fast neutrons. The investigations of optical properties in temperature range of (50-300) K and (1-50) mkm spectral area were carried out on infrared spectrophotometers. Radiation flow of fast neutrons was equal to 2•1018 neutron/cm2 and .electrons with 1MeV, 3 MeV, 50 MeV up to fluxes of 6•1017electron/cm2. Low temperature experiments were performed with application of liquid helium and nitrogen in the special cryostats for measurements of optical properties of experimental samples. Indicated phenomenon takes place at high and low temperatures as well at impurity different concentration and practically in all cases of irradiation by various energy electrons and fast neutrons. Earlier by different authors there have been shown, that noticeable phenomenon has quite common character in great number of ionic and typical semiconductor materials. We have developed the common mechanism of this phenomenon for un-irradiated semiconductors and implemented the quantitative calculations of distinctive parameter (E0), those are in a satisfactory agreement with experimental data. For the irradiated crystals picture get complicated and there takes place dependence: for un-irradiated and irradiated by electrons crystals, but for irradiation by huge flows of fast neutrons n≠1. Some processes are described when n=2. It has been shown, that in the case of InP, irradiated with electrons (Ф=1•1017el/cm2), the curve of optical absorption is shifted to lower energies. This is caused by appearance of the tails of density of states in forbidden band due to local fluctuations of ionized impurity (defect) concentration. Situation is more complicated in the case of InAs and for solid solutions with composition near to InAs when besides noticeable phenomenon there takes place Burstein effect caused by increase of electrons concentration as a result of radiation. We have shown, that in certain conditions it is possible the prevalence of Burstein effect. This causes the opposite effect: the shift of the optical absorption edge to higher energies. So in given solid solutions there take place two different opposite directed processes. By selection of solid solutions composition and doping impurity we obtained such InPxAs1-x, solid solution in which under radiation mutual compensation of optical absorption curves displacement occurs. Obtained result let create on the base of InPxAs1-x, solid solution radiation-resistant optical materials, which one of the basic characteristics- the long wavelength part of the fundamental optical absorption edge- does not change noticeably under hard irradiation.