Effect of Melt Stoichiometry on Shallow Acceptor Formation in Heavily Doped GaAs

The behaviour of group III, IV and VI dopants in vertical Bridgman grown GaAs was studied as a function of the stoichiometry of the melt. The melt composition was abruptly changed from stoichiometric to Ga-rich by intentional injection of gallium during the growth. In GaAs co-doped with Si and B, the Ga injection causes a drastic decrease of the free electron concentration which is explained by an increased concentration of As-sublattice acceptors. Spatially resolved photoluminescence (PL) results confirm this interpretation qualitatively as (SiAs)- and (BAs)-related modes dominate the spectra from the Ga-rich area of the sample. Pronounced PL peaks related to As-sublattice acceptors also appear in samples doped with B and Ge after Ga injection. The assignment of the PL modes was possible by taking account of the data in the literature and with respect to the results of Hall, Raman and mass spectrometric measurements. In GaAs:Sn and in group VI-doped samples, however, the Ga injection causes PL modes not previously reported