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+0) 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=19kbar) which correspond to an axial deformation ll=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 (7 and 8) and of the lowest minima of the conduction band (6 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=-(1.50.2) eV, b2=+(0.20.2) eV, d=d1+2 d2=-(4.60.2) eV, and d2=+(0.30.2) 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 (atk=0) and E1 [atk=(2a) (0,0,1)] to give the net pressure coefficients. We find C1+a1+a2=-(9.90.3) eV, E1+a1+a2=+(2.30.5) eV, and a2=-(0.40.3) 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|=131.5 eV. © 1979 The American Physical Society.