Dependence of the direct energy gap of GaP on hydrostatic pressure

Abstract

The dependence of the direct gap of GaP (Г 1 5 → Г 1) on hydrostatic pressure P up to 23 GPa is reported. The pressures were applied with a diamond anvil cell and measured using the ruby fluorescence technique. At 22.1 ± 0.3 GPa the material undergoes a transition to a phase opaque in the visible. The energy gap E 0(eV) = 2.76 + 9.7 × 10 -2P−35×10 -4P 2 (P in GPa) exhibits a sublinear dependence on P. The dependence of E 0 on the relative change of lattice constant (Δa/a 0) is more linear but still remains sublinear to a larger extent than for other tetrahedral semiconductors measured (Ge, GaAs, InP). The sublinearity found for GaP is well reproduced by band structure calculations based on a local empirical pseudopotential. We also report the calculated linear and quadratic shifts of the E 1 and the indirect gaps with Δa/a 0.