Millimeter-wave investigation of electronic conduction in semiconducting III-V compounds

Abstract

The small‐signal microwave conductivity of n‐type single‐crystal InSb, GaSb, InAs, and epitaxial GaAs under the influence of a heating dc field was studied experimentally at 4‐mm waves. Contrary to low‐frequency results, the millimeter‐wave conductivity of InSb at 78 K increases with increasing dc field as a consequence of relaxation effects. The anisotropy with respect to the direction of this field is reversed so that the conductivity for parallel dc and ac fields exceeds the conductivity for perpendicular fields. Mean momentum and energy relaxation times τ_m and τ_ε, respectively, are evaluated from the conductivity data: τ_ε, almost constant, is about 2×10⁻¹²sec, τ_m drops from 6.1×10⁻¹² sec and 2.6×10⁻¹² sec, depending upon sample mobility, to some 2×10⁻¹² sec when the electric field is increased from zero to 170 V/cm. Agreement of microwave τ_m with dc measured values is satisfactory. In GaSb at 300 K and 85 GHz, relaxation effects show up in a pronounced deviation of the parallel microwave conductivity from the differential conductivity in the field range from 1 to 3 kV/cm, indicating that the time constants for Γ‐L intervalley electron transfer are of the order of the reciprocal test frequency and that the Γ‐L intervalley coupling constant is around 3×10⁸ eV/cm. At low heating fields, the warm‐electron parameter β was measured for InSb at 78 K, GaAs at 300 K, and InAs at both temperatures by a microwave method. Positive values were found in InAs [78 K: (4.9±0.8)×10⁻⁷cm² V⁻²; 300K: 2×10⁻⁸cm² V⁻²], negative ones in GaAs [(1.1±0.6)×10⁻⁸ cm² V⁻²] and InSb [high‐mobility material (−1.9±0.6)×10⁻⁴ cm² V⁻²; low‐mobility material: −4.6×10⁻⁶cm² V⁻²]. The results are discussed in terms of various theories.