A photoluminescence study of Cd-related centers in InP

Abstract

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.

Low temperature photoluminescence characteristics of Zn-doped InP grown by metalorganic chemical vapor deposition

“…1,2 PL characteristics for the in situ Zn-doped InP was also reported, 8 however, the PL characteristics for samples doped close to or at the doping saturation level have not been reported yet.…”

“…8,9 A characteristic donor-acceptor transition, resulting from the presence of interstitial Zn atoms, was reported for the Zn-doped InP.…”

Evidence for enhanced zinc interstitial concentration in strain-relaxed heteroepitaxial indium phosphide

“…[13][14][15][16] This peak extends over the range 1.20-1.36 eV, but its peak energy is strongly dependent upon the optical excitation intensity. The D-A transition photon energy is 13…”

Hydrogen Passivation of Shallow Dopants in InP Studied by Photoluminescence Spectroscopy

“…Recalling the results on InP :Mg samples where we observed an energy shift of about 14 meV per decade change in excitation power, a shift of 7meV in InP:Zn samples leads to a conjecture that the donors present in the two samples are not the same. In Cd coped InP, a donor with E >56 meV has been previously reported [12]. We thus note that donors of higher ionization energy than the normally observed shallow donors are present in p type InP crystals.…”

“…The peak shift is calculated to be about 14 meV per decade change in excitation power. A peak shift of this magnitude suggests that the shallower center participating in this D-A pair transition has a higher ionization energy than the commonly observed shallow donors [ 12].…”