Pressure dependence of energy gaps and refractive indices of tetrahedrally bonded semiconductors

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Abstract
The pressure dependence of energy gaps for a number of elemental and compound semiconductors is investigated employing the empirical pseudopotential method. The compressibility and the empirical pseudopotential form factors appropriate for describing the band structure at normal pressure are the only required input parameters in this calculation. The calculated pressure coefficients of several critical-point band gaps for group IV and III-V compounds are generally in good agreement with experimental data. The results are then utilized, along with a Penn type of single-oscillator model for the dielectric constant, to calculate the pressure coefficient of the refractive index. The results are good for elemental semiconductors and reasonable for III-V compounds. Similar calculations of pressure coefficients of both the energy gaps and the refractive index for several II-VI compounds yield results which are less satisfactory. Possible reasons for this discrepancy are discussed.