A photoluminescence study of Cd-related centers in InP

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We report detailed studies of the low-temperature photoluminescence of Cd-related centers in InP. The samples consisted of Cd-diffused InP substrates as well as Cd-doped InP epitaxial layers grown by metalorganic chemical vapor deposition. Besides the previously identified 1.365-eV band, a new Cd-related band at a lower photon energy is reported. At 5.5 K, depending upon the excitation intensity, the peak position of this new band lies in the energy range 1.20–1.33 and 1.33–1.34 eV, respectively, in the substrates and in the epitaxial layers and it is broader compared to the 1.365-eV band. The peak position of the bands shifts to higher energy with increasing excitation intensity but the change in the peak energy per decade change in excitation intensity is much larger (50 meV) for the lower-energy band compared to the 1–2 meV shift for the 1.365-eV band. While the excitation dependence of the bands suggests a donor-to-acceptor pair recombination for their origin, we present arguments to show that the larger shift of the peak energy of the lower-energy band with excitation intensity is perhaps a consequence of the involvement of a deep donor in its origin as opposed to a shallow donor in the 1.365-eV band. In the case of InP:Cd substrates both the 1.365-eV band and the 1.20–1.33-eV band exhibit thermal quenching of luminescence above 100 K with an activation energy of 54±4 meV which is comparable to the ionization energy of 56 meV for the substitutional Cd acceptor, CdIn . From this we infer that both bands involve the CdIn acceptor in the recombination process. The identity of the deep donor in the 1.20–1.33-eV band and that of the recombination centers giving rise to the 1.33–1.34-eV band in the InP:Cd epitaxial layers are not known. In a preliminary comparison study on InP:Zn, similar, high- and low-energy Zn-related bands are observed. It is suggested that the deep donor is related to the group II impurity.