Optical Absorption in Single-Crystal Metastable (GaAs)1−x(Ge2)x Alloys: Evidence for a Zinc-Blende-Diamond Order-Disorder Transition

Abstract

Single-crystal metastable ${\left(\mathrm{GaAs}\right)}_{1-x}{\left({\mathrm{Ge}}_2\right)}_x$ alloys with $0<x<\mathrm{}1\mathrm{}$ have been grown on (100) GaAs substrates by use of ultrahigh-vacuum ion-beam sputter deposition. Optical-absorption measurements showed that the direct gap $E_0$ exhibited a large negative $V$-shaped bowing as a function of $x$ with a minimum $E_0\simeq 0.5$ eV near $x=0.3\mathrm{}$. A zinc-blende to diamond-lattice order-disorder transition model is proposed as a possible explanation for these results.