Growth and optical properties of single-crystal metastable (GaAs) 1− x Ge x alloys

Single-crystal metastable (GaAs)1−xGex alloys with 0≤x≤1 have been grown on (100) GaAs substrates using ultra-high-vacuum ion-beam sputter deposition. Optical absorption measurements showed that the direct gap E0 exhibited a large negative, but nonparabolic, bowing as a function of x with a broad minimum E0≃0.5 eV near 35 mole % Ge. Raman results exhibited a nonlinear ‘single-mode’ behaviour, with the longitudinal and transverse optical modes becoming degenerate at x = 1.