ESR of the doubly ionized Cr acceptor and infrared luminescence of Cr in GaP:Cr

Abstract

After optical excitation a broad isotropic electron-spin-resonance (ESR) signal with $g=1.999\mathrm{}$ has been observed in chromium-doped GaP. It is attributed to an isolated ${\mathrm{Cr}}^{+}$ ($3d^5$) center, presumably on a Ga site, which may be viewed as the doubly ionized Cr acceptor. The low-energy threshold for optical ${\mathrm{Cr}}^{+}$ generation is found to be at 1.15 eV. The ${\mathrm{Cr}}^{+}$ generation is interpreted as electron excitation from the valence band into the singly ionized Cr acceptor, ${\mathrm{Cr}}^{2+}$ ($3d^4$). Photoluminescence (PL) measurements on GaP:Cr revealed an emission band with a sharp zero-phonon line at 1.03 eV followed by several phonon replicas. This PL is ascribed to the radiative capture of free (or loosely bound) carriers at one of the deep Cr centers. The similarity of the ESR and PL data for GaP:Cr and GaAs:Cr is demonstrated.