Piezospectroscopic and magneto-optical study of the Sn-acceptor in GaAs

Abstract

The photoexcited luminescence spectrum of Sn-doped GaAs is studied as a function of the doping range, the temperature, and external stress and magnetic fields. Two emissions due to the Sn acceptor can clearly be distinguished: the (${A}^{0},X$) bound-exciton recombination and the (${D}^{0},{\mathrm{Sn}}^{0}$) pair recombination. The bound exciton exhibits an excited state 1.3 meV above the ground state. The angular momenta of the ground and excited state are $j=\frac{1}{2} \mathrm{and} \frac{5}{2}$. Only one Sn acceptor is found in the doping range ${10}^{14}$-${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and the energy interval 20-400 meV. This acceptor with a binding energy of 167 meV was found to have lattice symmetry. The deformation potentials of the acceptor, which describe the splitting of the bound-exciton line as well as the shift of the acceptor emission and its polarization, are ${a}^{\ensuremath{'}}=\ensuremath{-}8.0\ifmmode\pm\else\textpm\fi{}0.03$ eV, ${b}^{\ensuremath{'}}=\ensuremath{-}0.195\ifmmode\pm\else\textpm\fi{}0.02$ eV, and ${d}^{\ensuremath{'}}=\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}0.15$ eV. The magnetic measurements lead to an effective $g$ value, ${g}_{\mathrm{eff}}=\ensuremath{-}0.46\ifmmode\pm\else\textpm\fi{}0.02$, for the bound electron and the parameters $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\kappa}}=0.39\ifmmode\pm\else\textpm\fi{}0.03$, and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}=0.035\ifmmode\pm\else\textpm\fi{}0.005$ for the tin bound hole. The most remarkable magnetic property of the Sn acceptor is the occurrence of a diamagnetic splitting between the $|{m}_{j}|=\frac{1}{2} \mathrm{and} \frac{3}{2}$ states: The first observation of a diamagnetic splitting of bound holes. This splitting is interpreted as being due to the fourfold degeneracy of the valence band. The magnetic properties of the bound exciton are completely explained by the model of a pseudodonor, where an ${\mathrm{H}}^{\ensuremath{-}}$-like ${\mathrm{Sn}}^{+}$ center binds an electron. Evidence for observation of direct recombination to this new type of center is given.