Photoluminescence identification of the C and Be acceptor levels in InP

Low dose (5x10⁹-5x10¹¹ cm^-2) ion implantations of several ions including C, Be, Mg, and Mn have been performed into high purity epitaxial and bulk InP samples. A comparison of the low temperature (1.7-20 K) photoluminescence spectra of these deliberately doped samples was made to similar spectra of undoped high purity InP grown by LPE, PH₃-VPE, and LEC techniques in order to identify the residual acceptors in the undoped samples. Ionization energies obtained for the C, Be, and Mg acceptors (assuming E_g=1.4237 eV) were 44.6 ± 0.3, 41.3 ± 0.3, and 41.0 ± 0.3 me_gV, respectively. These valu were compared to the ionization energy of the dominant residual acceptor in LPE InP, which also occurs in LEC, polycrystalline, and PH₃-VPE material. This acceptor level was first reported in LPE InP by Hess et al. in 1974, who denoted it A₁; it has widely been assumed to be C. The value we measure for the ionization energy of A₁, which is 41.2 ± 0.3 meV, however, matches that of Mg and Be and not C. We conclude that C is almost never present as a residual acceptor in undoped InP, and that the residual level in LPE and other material is Mg, or possibly Be. Similar measurements on Si and Sn doped samples showed no evidence of any Si or Sn acceptor level. The Mn acceptor peak was observed to occur at 1.19 eV.