Effects of high pressure, uniaxial stress, and temperature on the electrical resistivity of n-GaAs

Abstract

We have used a piston-cylinder apparatus to measure the resistivity of GaAs plates as a function of stress up to 50 kbar. Below 37 kbar our stress is hydrostatic, and above 37 kbar it has a uniaxial component. For sulfur-doped, floating-zone-purified GaAs the resistivity of (111) plates rises until it attains a constant value with increasing stress at 38 kbar, whereas for (100) plates it decreases above 38 kbar. We conclude that conduction takes place in [100] valleys at high pressure. The ratio of the "saturation" resistivity of (111) plates to resistivity at 1 atm is due to both the lower mobility in the [100] valleys and carrier "freeze-out" on sulfur donors which are deep with respect to the [100] valleys. The amount of carrier "freeze-out" was determined from the temperature dependence of the resistivity at 50 kbar. We conclude that the mobility in the [100] valleys is about 110 cm²/V-sec. We have used an empirical equation of state to correct for the pressure dependence of the compressibility and have obtained a value of 8.4 eV/ (unit strain) for the rate of closure of the [000] and [100] band-edge points. Measurements on GaAs in which the Fermi level is locked to a deep donor at atmospheric pressure yielded a value of 8.15 eV/ (unit strain) for the upward motion of the [000]-band minimum with pressure.