Pressure and temperature dependences in p-ZnAs2 at high pressures

Abstract

Zinc diarsenide (ZnAs 2 ) is a II-V semiconductor compound, which crystallizes in the monoclinic sys tem [1] and has the band gap energy E g ≈ 1 eV. The structure peculiarity of ZnAs 2 is the presence of bands between As atoms, which form zigzag chains elon gated along the c axis (crystallographic orientation [100]), together with Zn-As bonds; this peculiarity is responsible for the significant anisotropy of electrical and optical properties. Along with the high transpar ency of ZnAs 2 in a wide range of wavelengths in the IR region (1.4-20 μm), the possibility of developing a solid state laser on its basis is of the greatest interest for practical use [2]. Induced emission at a wavelength of 1.235 μm was obtained from ZnAs 2 single crystals upon electronic pumping.Among the publications dedicated to the study of ZnAs 2 at high pressures, the work by Clark and Pisto rius [3] is well known; they measured the resistivity of polycrystalline ZnAs 2 in Bridgman anvils at pressures to 11 GPa at 25°С. However, the I-II phase transition to P ≤ 11 GPa was not discovered by resistometric measurements. Therefore, it was of interest to deter mine resistivity and Hall effect in the single crystal samples of ZnAs 2 . EXPERIMENTALThe measurements were performed at hydrostatic (to P ≤ 9 GPa) and quasi hydrostatic (to P ≤ 50 GPa) pressures. The hydrostatic pressure was generated by a compression unit with a stress of 500 ton force. The dependences of resistivity ρ and Hall coefficient R H were measured simultaneously in a Toroid anvil/trun cated hemisphere type high pressure apparatus (HPA), which was placed in a multiturn solenoid with the magnetic field intensity H ≤ 300 kA/m [4]. The sizes of the samples were 3 × 0.8 × 0.8 mm. A mixture of ethanol-methanol in a ratio of 4 : 1, which is hydro static to the pressures P ≤ 9 GPa, was used as a pressure fluid. The resistivity, Hall coefficient, and pressure measurement errors were ±3, 3.5, and 3%, respec tively. The measurement procedure was described in more detail elsewhere [4,5].Pressure from 15 to 50 GPa was produced with the use of a high pressure chamber (HPC) with anvils of the plane-rounded cone type [6,7], made from the carbonado type synthetic polycrystalline diamonds. These anvils are good electric conductors; this fact makes it possible to measure the pressure and tempera ture dependences of the resistance of a sample placed between the anvils, which are used as contacts. This procedure allowed us to cyclically change pressure applied to the sample. This makes it possible not only to study conductivity changes under changes in pres sure but also to analyze possible changes in the sample structure based on irreversible changes in electrical properties (the prehistory of the sample). The mea surements were performed in a temperature range of 77-400 K.Pressure was determined from the formula P = AF/πa 2 , where F is the applied force, а is the contact radius, and A is an empirical coefficient (in our case, Abstract-Kinetic effects in p ZnAs 2 were measured at hydrostatic ...