The Effect of Strain in Pseudomorphic PSILICON(1X) Germanium(x): Physics and Modeling of the Valence Bandstructure and Hole Transport
Abstract
The physics of hole transport in pseudomorphic Si_{1x}Ge_ {x}//(001)Si is investigated by Monte Carlo simulation. The Monte Carlo method developed in this work takes into account several aspects of the strained ptype system which qualitatively distinguish it from an ntype system. These include: (1) the valence band system is described using a three band vec kcdot vec p method which gives an accurate representation of the strongly coupled heavy hole, light hole and split of hole states; (2) the valence band deformation potential theory is used to determine both the strain effects on the bandstructure and the holephonon scattering rates in both strained and unstrained materials; (3) the scattering rates are anisotropic, depending upon the direction of flight and are calculated on a mesh which exploits the symmetry of the system and (4) the postscattering states are determined from a probability distribution which depends not only on the scattering angle, but also upon the initial direction of flight. The Monte Carlo method is used to make a detailed study of the effect of strain and alloying on hole transport in light to moderately doped pseudomorphic Si_{1x}Ge_ {x}(0 <=q x<=q 0.4) grown on (001)Si, subjected to electric fields in the range of 120 kV/cm, at 300 K. The scattering mechanisms considered are: alloy scattering, acoustic phonon scattering and both SiSi and GeGe optical phonon scattering. Each of these mechanisms can drive both intra and interband scattering within and between all of the top three valence bands. The combined effects of strain and alloying are found to produce a monotonic increase in hole mobility and temperature, which at the highest Ge content alloy studied, Si_{0.6}Ge _{0.4}//(001)Si, are comparable to the hole mobility and temperature in bulk Ge. A slight greater carrier velocity is found for inplane transport than for perpendicular transport. The results of this analysis are used to estimate the high frequency performance of an npn Si/Si_{1x}Ge _{x}/Si DHBT, where an approximate twofold increase in f_{max } is found over that in a comparable state of the art Si BJT. The work concludes with a brief analysis of hole transport in strained GaAs. This being a polar semiconductor results in qualitatively different hole transport characteristics, which are contrasted with the findings for the covalent Si_{1x}Ge _{x}.
 Publication:

Ph.D. Thesis
 Pub Date:
 January 1990
 Bibcode:
 1990PhDT.......186H
 Keywords:

 SILICON GERMANIUM;
 GERMANIUM;
 Engineering: Electronics and Electrical; Physics: Condensed Matter