SCREENING IN A DELTA-DOPED SEMICONDUCTOR

The screening of an impurity in the quasi-two-dimensional (2D) electro n gas in a delta-doped semiconductor structure is investigated. The sc reened impurity matrix elements are calculated and compared using thre e different approaches: the 2D random phase approximation (RPA), the c orresponding 2D Thomas-Fermi theory and a quasi-three-dimensional (3D) Yukawa-like screening model. It is found that the 2D Thomas-Fermi the ory differs from the RPA result, even in the limit of low q vectors, i f more than one subband is occupied. This result is explained analytic ally by closely examining the q --> 0 limit of the dielectric tenser. The 2D Thomas-Ferni theory is shown to represent a poor approximation to the RPA whereas the quasi-3D screening model agrees well with the R PA results for not too small q vectors. Furthermore, this model reduce s computing times by orders of magnitude in comparison with the RPA. T hus, our 3D screening model considerably simplifies the calculation of impurity scattering rates in the investigation of the electron mobili ty in a delta-doping layer. (C) 1998 Academic Press Limited.