The electrical properties of zinc selenide

Abstract

The electrical conductivity and Hall coefficient of a variety of single crystals of zinc selenide have been measured. As-grown, undoped crystals have a resistivity ( approximately 1012 Omega cm) which is too large for successful Hall measurements to be made. However, after heat treatment at 850 degrees C in molten zinc, the resistivity of a sample is reduced to about 10-1 Omega cm. The samples are fairly heavily compensated. The Hall mobility of the free electrons is about 530 cm2 V-1 s-1 at room temperature when optical mode scattering is the dominant mobility-limiting mechanism. At lower temperatures, ionized impurity scattering becomes dominant. Crystals containing grown-in impurity donors such as indium, gallium and chlorine have also been investigated, as have crystals containing aluminium. Increasing the concentration of aluminium leads to overlap of the shallow donor wavefunctions with consequent impurity banding and the production of a degenerate semiconductor. Increasing the concentration of indium, gallium or chlorine is accompanied by anomalous behaviour.

The Defect Structure of Pure and Doped ZnSe

“…If the defect structure of sample 5 would correspond to range 2, then the room temperature electron concentration of crystals quenched to room temperature after annealing at high temperature with different Pzn should be almost equal to that at high temperature because the Vse x level is only 0.008-0.02 eV below the conduction band (18)(19)(20). This was not observed for sample 5: It had almost no free carriers after cooling.…”

Electron mobility in ZnSe single crystals

“…However, it has been noted [4,5] that experimental values of mobility at T < 100 K are higher than those calculated in view of scattering by impurity ions. This discrepancy was explained [4] by decreasing the effective concentration of ionized centres due to the formation of dipoles as a result of donor-acceptor interaction.…”

“…The improvement in the technology of both growing and subsequent heat treatment of n-ZnSe crystals in Zn melt allowed the electron mobility to be increased to (8)(9)) × 10 3 cm 2 /(V s) at 77 K [6,7] and up to the maximum value of 1.2 × 10 4 cm 2 /(V s) at 55 K [6]. The discrepancy between theory and experiment was also observed in the region of scattering by phonons [5], where the experimental values of mobility reached the value of 600 cm 2 /(V s) at 300 K. It was shown [3] that the discrepancy in the region of scattering by impurity ions was due to the inadequacy of known scattering theories based on the Born approximation, since this approximation is valid for ZnSe at T > 100 K, where the scattering by phonons is predominant. A polaron effect was taken into account in [3] in order to co-ordinate the theory with experiment in the region of phonon scattering.…”

Impurity centers in ZnSe:Na crystals

“…2). If Na Zn defects play a role of acceptors in DAP transitions responsible for the R-band, then, the activation energy of the donors involved in these transitions is equal to 1874 meV at 10 K, and 20 76 meV at 100 K. This value is considerably lower than the activation energy of common residual donors in ZnSe, such as Cl, Br, I, in which activation energy is about 27 meV [10][11][12]. Taking into account these data, one can suggest that Na i centers play a role of donors in the DAP responsible for the R emission band.…”

“…This value corresponds to the activation energy of such residual donors as Cl, Br and I [10][11][12]. The decrease of the Q-band intensity against the R band by increasing the doping level (see Fig.…”