Transport of hot carriers in semiconductor quantized inversion layers

Abstract

The transport of warm and hot carriers in quantized inversion layers has recently become of considerable interest, due in part to the quasi-two-dimensional nature of the carrier system and to the multitude of subbands present. Generally, the number of carriers in the inversion layer is sufficiently large that carrier-carrier scattering maintains a quasi-Maxwellian for the isotropic part of the distribution function, but the inter-subband interactions are sufficiently weak that each subband possesses a separate electron temperature. The treatment of carrier transport can be naturally separated into two regimes. In the first, the carriers are hot. In this regime, the transport can be found from energy and momentum balance equations and the transport differs little from a classical three-dimensional model, except in the field region in which inter-subband transfer of carriers is important. In this field range, subtle changes in the velocity-field curve are observed and significant effects are found in the microwave conductivity at frequencies on the order of the inter-subband repopulation rate. In the warm electron regime, however, for low and moderate electric fields, the degenerate nature of the carrier distribution function must be considered. Although the electron temperature concept remains valid in this regime, the agreement between theory and experiment is not good and the lack of this agreement makes it difficult to assess the physical processes occurring. The situation is complicated at low temperatures where many of the scattering mechanisms are not fully understood and the carrier densities and transport can show activation behavior. This lack of understanding is especially true in warm carrier magneto-transport. For this reason, care must be exercised in evaluating the role played by the electric field. In this paper, these various regimes are discussed and compared to the available experimental data.