Deformation potentials of the direct and indirect absorption edges of GaP

We present uniaxial-stress experiments performed on the direct and indirect exciton spectrum of GaP. Two direct transitions (E₀ and E₀+Δ₀) and three indirect phonon-assisted transitions (LA, TA, and TO phonon modes) have been investigated at 77 and 4.2^∘{}K, respectively. Very-high-stress conditions have been achieved in this work ($X=19$kbar) which correspond to an axial deformation δll=2×10^-2, reaching the elastic limit of the material. We have been able to determine all linear and nonlinear deformation potentials that describe the stress dependence of the topmost valence bands (Γ₇ and Γ₈) and of the lowest minima of the conduction band (Γ₆ and X₆). The stress splitting of the valence band is produced by (i) the orbital-strain interaction, which is described by two deformation potentials b₁ and d₁, and (ii) the stress-dependent spin-orbit interaction which is described by two extra parameters b₂ and d₂. We find b=b₁+2 b₂=-(1.5±0.2) eV, b₂=+(0.2±0.2) eV, d=d₁+2 d₂=-(4.6±0.2) eV, and d₂=+(0.3±0.2) eV. The effect of hydrostatic deformation is again interpreted in terms of two deformation potentials a₁ (orbital-strain interaction) and a₂ (strain-dependent spin-orbit interaction). They combine with two hydrostatic deformation potentials for the conduction band C₁ (at k=0) and E₁ [at k=(2πa)(0,0,1)] to give the net pressure coefficients. We find C₁+a₁+a₂=-(9.9±0.3) eV, E₁+a₁+a₂=+(2.3±0.5) eV, and a₂=-(0.4±0.3) eV. The shear deformation potential E₂ of the indirect minimum of the conduction band has been obtained from the same series of measurements. We find E₂=+(6.3+0.9) eV. Lastly, the stress-induced coupling between the lowest minimum of the conduction band (X₆) and the next higher minimum (X₇) has been observed, and is described by a single deformation potential E₃. We find |E₃|=13±1.5 eV.