Trends in band-gap pressure coefficients in chalcopyrite semiconductors

We present the results of a first-principles calculation of the direct band-gap pressure coefficient ag for a series of Ga and In semiconductor compounds with both the chalcopyrite (e.g., CuGaSe₂ and CuInSe₂) and the zinc-blende structures (e.g., GaAs and InAs). We found good agreement between the calculated and experimental pressure coefficients. We found that ag in chalcopyrites are dramatically reduced relative to zinc-blende compounds, and that the G→aIn substitution lowers ag in chalcopyrites more than in zinc-blende compounds. As a result, the empirical rule suggested for zinc-blende compounds, stating that for a given transition (e.g., Γ₁₅ᵥ→Γ1c) ag does not depend on substitutions, has to be modified for chalcopyrites. Based on our results we question the currently accepted experimental value for CuInTe₂ (2.2 meV/kbar); we calculate this value to be close to 5.9 meV/kbar.