Improved properties of melt-grown GaAs by short-time heat treatment

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Abstract
A large improvement of the properties of undoped melt‐grown GaAs is obtained by short‐time heat treatment with a SiO2 encapsulating layer. C‐V and Hall measurements showed that deep acceptor traps lying at 0.23 eV below the conduction band were contained with the range of free‐carrier concentration in the starting materials but they are completely removed by heat treatment above 800 °C. The photoluminescence efficiency for near‐gap transition is improved considerably after heat treatment to approach that of solution‐grown material. A highly doped thin surface layer was formed in most samples annealed above 850 °C. The introduction of a large concentration of shallow donors, however, never contributes to the intensity increase of the near‐gap emission but induces low‐energy broad‐band emissions peaked at 1.30 and 1.15 eV. The behaviors of native defects responsible to the nonradiative centers are explained as follows: (i) in undoped material the defects, presumably Ga vacancies, are solely annealed out and (ii) if a large concentration of donors are presented, annealing accompanies the formation of more stable complex defects.