VALENCE-BAND STRUCTURES OF HEAVILY-DOPED STRAINED GEXSI1-X LAYERS

Valence-band structure and density-of-state (DOS) effective mass are calculated for heavily p-type-doped Si and strained GexSi1-x layers grown on (100) Si. At low doping values calculations have been made by earlier authors and the results agree with the published values of DOS mass by these authors. The Fermi energy E(F) measured from the valence-band edge has been calculated using our values of DOS effective mass. At 10(20) cm-3 doping level the value is 77.3 meV compared with 80 meV determined from luminescence experiments. The value of E(F) obtained by using the normally accepted value of 0.57 for the hole effective mass in Si is more than the experimental value by a factor about 2, i.e., the calculations reduce the discrepancy from 100% to less than 4%. The effective barrier height of (p+-Ge0.42Si0.58)/(p-Si) internal photoemission photo detector has also been calculated using our calculated value of the DOS hole mass. The calculated value is in reasonable agreement with the experimental value. The values of the band parameters and of deformation potentials are known only for small values of k and energies. These values have been used at large doping concentrations where k and energy are also large. The agreement of the theory with experiment suggests that the values of the parameters are valid approximately at higher energies also.