Negative dynamic differential conductivity at the cyclotron frequency in Ga_1−x Al_xAs under conditions of ballistic intervalley electron transfer

Abstract

It is theoretically shown that under certain conditions a cyclotron resonance maser can be fabricated based on n-Ga_1−x Al_xAs-type materials. Low temperatures and strong crossed fields (E⊥H) are considered. In these fields the electrons in the lower (light) valley of the conduction band dynamically (ballistically) transit the band up to the onset energy of intervalley scattering ɛ ₀. Studies were carried out on solid solutions with composition 0<x<0.39 (ɛ ₀=(2–17)ℏω*, where ℏω* is the intervalley phonon energy). The magnitudes of the E and H fields were varied within the limits E=5–20 kV/cm and H=6–40 kOe. This produced a smooth change in the transit conditions in the passive region (ɛ<ɛ ₀), which makes it possible to obtain the desired frequency dependence of the differential conductivity (DC), σ(ω). As our studies show, previously unknown, interesting peculiarities of the hot electron system appear under these conditions.