GROWTH OF ZNTE BY METALORGANIC VAPOR-PHASE EPITAXY - SURFACE-ADSORPTION REACTIONS, PRECURSOR STOICHIOMETRY EFFECTS, AND OPTICAL STUDIES

The metalorganic vapor phase epitaxy growth of ZnTe by di-isopropyl-te lluride and di-methyl-zinc (Me(2)Zn) precursors is investigated by stu dying the epilayer growth rate as a function of both growth temperatur e and precursor transport rates. The ZnTe growth is a thermally activa ted process involving the heterogeneous pyrolysis of both Zn and Te al kyls onto the ZnTe surface. The growth rate dependence on growth condi tions is explained in terms of surface adsorption-desorption reactions , assuming that the incorporation of Zn and Te atoms into ZnTe takes p lace through their selective adsorption on different surface lattice s ites, There is also evidence that the occurrence of a competitive spec ies for the surface adsorption of Zn atoms, which is identified as the CH3 (methyl) radical, is produced by the pyrolysis of Me(2)Zn. Photol uminescence (PL) and absorption measurements performed on ZnTe allow t o identify two new donor-acceptor pair (DAP) bands, originated from th e recombination of a Ga donor with two acceptor centers, whose ionizat ion energies are 56 meV for the higher energy band and around 140-150 meV for the lower energy one. Hall measurements show that the 56 meV a cceptor is responsible of the p-type conductivity of the layers. The n ature of the impurities originating such PL features is discussed with the support of secondary ion mass spectrometry. It is shown that Ga, Si, and C are dominant impurities in the layers, whereas Cu does not o ccur in our ZnTe. Unintentional C doping occurs in ZnTe as a consequen ce of the strong methyl and iso-propyl radical surface adsorption. We show that C is incorporated as an acceptor in ZnTe, originating the DA P bands observed in the PL spectra. Within this view, the 56 meV ioniz ation energy acceptor is tentatively assigned to substitutional C atom s on Te lattice sites. (C) 1997 American Institute of Physics.