Quantum effects in silicon-germanium p-type heterostructures with quantum wells of different widths

Abstract

The magneto-quantum and quantum interference effects in a two-dimensional gas of p-type charge carriers are studied for three quantum wells made of practically pure germanium in a Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructure. The quantum well widths were 8 nm for sample I, 19.5 nm for sample II, and 25.6 nm for sample III. The dependences of resistance on the magnetic field for all samples exhibit Shubnikov–de Haas oscillations. Their analysis made it possible to calculate the kinetic characteristics of charge carriers for the cases of one (sample I) and two occupied subbands (samples II and III). In the region of weak magnetic fields (B < 0.1 T), the effect of weak localization of holes was revealed, which determines the negative magnetoresistance and the increase in resistance with decreasing temperature. The manifestation of the charge carriers interaction effect at various temperatures and magnetic fields is discovered and analyzed. A transition from the diffusion mode of manifestation of the quantum correction to the intermediate, and then to the ballistic mode is observed. In all regions, the behavior of the quantum correction due to the charge carriers interaction effect is in good agreement with modern theoretical predictions. The temperature dependences of the hole-phonon relaxation time are calculated. In weak magnetic fields, with an increase in the temperature of the 2D system, a transition from the “partial inelasticity” mode, characterized by the dependence τhph−1∝T2, to the small-angle scattering mode, described by the relation τhph−1∝T5, takes place. In stronger magnetic fields for samples with two occupied subbands, the dependence τhph−1∝T3was observed. Possible explanations for this dependence are presented.