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Impurity states and defects in layered semiconductors GaSe and InSe


Author: Evtodiev Igor
Degree:doctor habilitat of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2010
Scientific consultants: Valeriu Canţer
doctor habilitat, professor, Institute of the Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova
Mihail Caraman
doctor habilitat, professor, Moldova State University
Institution: Moldova State University
Scientific council: DH 30-01.04.10-23.04.09
Moldova State University

Status

The thesis was presented on the 17 September, 2010
Approved by NCAA on the 4 November, 2010

Abstract

Adobe PDF document0.95 Mb / in romanian

Summary

In the present thesis are presented complemented results of the analysis of the structure of optical, photoelectrical and luminescent properties of two representatives of the layered class materials of type AIIIBVI-GaSe and InSe, doped and un-doped with elements from te groups I-VII. Based on the measurements of structure with help of diffraction of X rays and of the FTIR spectrums in a large domain of number of waives it was determined that the initial GaSe crystals are of polyphase type. It is shown that that phase transactions ε-γ and ε-δ are happening as a result of mechanical action on the crystals and at their splitting. Introduction of the low concentration of the impurity atoms of the impurity (Sn, Cu) atoms leads to the growth of the parameter „a” and to the low decreasing of the „c” parameter for the hexagonal grating of the ε-GaSe crystals. Cd (Cu) impurities with quantities of 0.50% even more leads to the formation of the CdGa2Se4 clusters. Are determined the wave numbers of the optical fundamental phonons for impurities from these crystals.

Study of the absorption, reflection and photoluminescence optical spectrums are showing that the red margin of the fundamental absorption band of the doped and un-doped crystals with impurities from the groups I-VII is formed of excitons of big radius. Are determined the parameters of the excitons (binding energy, effective mass, localization energy of the excitons) as well as the type of the optical transaction of the studied compounds. Red wing of the exciton band is formed of the interaction of the excitons with the phonons. In the work was also determined the constants of these interactions. Optical absorption bands are formed of impurity elements (Li, K, Cu, Cd, Zn, Sn, Bi, Mn) and are directly adjoining with exciton bands. From the analysis of the optical absorption spectrums of the photoluminescence is determined the energy of the acceptor levels created by impurities inside interdicted of GaSe and InSe.

Introduction of the Cu, Cd, Sn in GaSe and InSe impurities leads to the increase by 2-3 orders of the concentration of the majoritary charge carriers. This way, the doping of the GaSe with 0.05 % at. Cd leads to the growth of the concentration of the holes at the normal temperature from 3•1012 cm-3to 4•1015 cm-3. At the same time the increase of the concentration of the Cd atoms from 0.01 % at. till 0.05 % at. leads to change of the type of the majority charge caries from n to p for the InSe. From the analysis of the dependency of the electrical conductivity of the temperature in the interval from 80K to 300K are determined the energy levels created by Cu, Cd and Sn impurity atoms localized in the interdicted band of GaSe and InSe. Levels created by the impurity atoms are determining also the photoelectical properties of the crystals. This way the increase of the concentration of the Cu atoms till 0.20 % at. leads to the growth by 100 times f the photosensibility of the ε-GaSe crystals at the room temperature. Further increase of the Cu atoms concentration leads to the formation of the localized states on the surfaces of the layered packets by which intensively are recombining the charge non-equilibrium carriers.

From the spectral analysis of the of the photoluminescence, its thermal extinguishing and the termically stimulated luminescence are determined the recombinatory levels created by the proper defects in the ε-GaSe and γ- InSe un-doped crystals and respectively of the levels created by the impurity atoms (Cu, Cd, Sn) in these crystals.

Using the method of termic oxidation of the thin layers of the metal were created heterojonctions In2O3, SnO2, ZnO, CdO, TiO2, Bi2O3-ε-GaSe and In2O3, SnO2-γ-InSe and studied the mecanisms of passing of the current through the heterojonction as well as their photoelectrical properties. From the analysis of the relaxation curves of the photocurrent, spectral distribution of photovoltage and optical absorption were determined the types of relaxation for these structures corresponding to the high photosensibility in the UV domain of the spectrum and respectively the average free run of the non-equilibrium charge carriers at the transition band.

Main results are published in 91 scientific works. Thesis is written in Romanian language, contains 292 text pages, 160 figures, 27 tables and 346 bibliographical references.