A hydrogen-stretching vibration at 2688 ${\mathrm{cm}}^{\mathrm{-}1}$, previously observed in heavily-carbon-doped GaAs grown by metal-organic molecular-beam epitaxy and assigned to a defect complex that contains carbon and hydrogen, has been studied by infrared-absorption spectroscopy. The absorption at 2688 ${\mathrm{cm}}^{\mathrm{-}1}$ has been found to be preferentially polarized along a particular 〈110〉 axis in the (001) growth plane. We propose that this band is due to a complex that is aligned at the growth surface and then maintains its alignment as the crystal is grown. The annealing of the 2688-${\mathrm{cm}}^{\mathrm{-}1}$ band and its alignment have been examined. We also find that the 2688-${\mathrm{cm}}^{\mathrm{-}1}$ complex can be formed by annealing heavily-carbon-doped GaAs between 500 and 650 °C in the presence of hydrogen. These results provide insight into the interactions of carbon and hydrogen in heavily-carbon-doped GaAs and lead us to tentatively assign the 2688-${\mathrm{cm}}^{\mathrm{-}1}$ band to a (${\mathrm{C}}_{\mathrm{As}}$${)}_2$H complex. We suggest that the annealing of this center and of its alignment is due to the dissociation and reassociation of ${\mathrm{C}}_{\mathrm{As}}$ pairs that are controlled by the presence of hydrogen.

• Received 24 August 1993

DOI:https://doi.org/10.1103/PhysRevB.49.2469