Native Defect Nature of Electrical Centres in Low-Resistivity Zinc Selenide

Abstract

Hall effect, electric conductivity and electron mobility in n-ZnSe crystals, annealed in Zn melt at temperatures from 500 to 950 C, are studied in the temperature range from 55 to 500 K. The sharp increase of the shallow donor concentration is accompanied by a decrease of their compensation from K N A aN D 0X91 to 0.35, and of the activation energy E D from 28 to 9 meV, as the annealing temperature of n-ZnSe crystals increases above 650 C. At low annealing temperatures, the conductivity of n-ZnSe is determined by shallow non-controlling donors such as Al Zn , Ga Zn , In Zn . The concentration of V Zn native defects compensating the shallow donors is sharply decreased and the concentration of the V Se shallow donors determining the conductivity of crystal is sharply increased, as the annealing temperature increases above 800 C. The decrease of annealing temperature of the samples below 650 C results in a drastic decrease of the conductivity of the crystal, a decrease of electron concentration, and abnormally low mobility values. The observed anomalies of transport effects are found to be caused by the presence of a random potential relief in n-ZnSe samples.ZnSe single crystals grown by various methods have a high resistivity r % 10 8 to 10 10 W cm, as they are strongly compensated [1 to 3]. High-temperature annealing in liquid Zn sharply reduces their resistivity [4]. It was supposed previously that the increase of conductivity in the process of such a thermal treatment is caused by a decrease of the degree of compensation of unknown shallow donors, the concentration of which is changed slightly. On the other hand, the result of excitonic spectroscopy of n-ZnSe crystals annealed in a Zn melt have convincingly shown that occupation of acceptor defects V Zn leads to a generation of the shallow donor V Se [5]. In this work, we show that native donor type defects, selenium vacancies, whose compensation increases sharply during such annealing, are the shallow donors determining the high conductivity of n-ZnSe crystals annealed in a Zn melt.The n-ZnSe samples were prepared by long-term (100 h) high-temperature (from 500 to 950 C) treatment of the originally high-ohmic r % 10 10 W cm monocrystals in a zinc alloy. After the treatment, the samples were instantaneously cooled down to 20 C. Zn diffusion in ZnSe is caused by Frenkel-type defects, and the self-diffusion coefficient D Zn does not depend on the partial pressure of the components above the solid phase. In the temperature range from 750 to 1150 C and the Zn vapor pressure range of 10 mPa to 80 kPa, the self-diffusion coefficient is D Zn (cm 2 as 9X8 exp À3X0 eVakT).

Development of AIIBVI Semiconductors Doped with Cr for IRLaser Application

“…The n-ZnSe samples were prepared by long-term high temperature treatment (500 -950 QC) of the originally high ohmic (p = 101(0 cm) single crystals in zinc melt. The self diffusion coefficient is Dzn = 9.8 (cm 2/s) exp(-3 eV/kT) [8]. Increasing of the duration of the treatment of the ZnSe crystals causes the increase of the electron concentration which reach saturation after 100 hours.…”

Development of AIIBVI Semiconductors Doped with Cr for IR Laser Application

“…The self-diffusion coefficient is D Zn = 9.8 (cm 2 /s) exp (--3 eV/kT) [8]. Increasing duration of the treatment of the ZnSe crystals causes an increase of the electron concentration which reaches saturation after 100 h. Diffusion of Cr from a gaseous source (CrSe) was used for doping the CdSe specimens, allowing to maintain a constant level of surface Cr concentration during a 100 h diffusion anneal.…”