Field effect on electron emission from the deep Ti donor level in InP.

Abstract

The effect of electric field on the thermal emission of electrons from the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ deep donor level in InP has been investigated. Double-correlation deep-level transient spectroscopy as well as differential-isothermal-capacitance transient measurements have been carried out on low-pressure--metalorganic-chemical-vapor-deposition-grown InP:Ti samples. It is found that the emission rates are strongly field dependent increasing by up to a factor of 17 corresponding to an increase of the field by a factor of 3.5 in the measured temperature range of 260 to 340 K. The experimental data are well fitted with a Poole-Frenkel model employing a three-dimensional square-well potential associated with the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ level with a radius r=4.6 nm. The fit of this model to the experimental data yields variations in the activation energy, \ensuremath{\Delta}E=0.48\ifmmode\pm\else\textpm\fi{}0.02 eV to 0.57\ifmmode\pm\else\textpm\fi{}0.02 eV, depending upon the actual field strength. An extrapolated zero-field \ensuremath{\Delta}E(0)=${\mathit{E}}_{\mathit{C}}$-${\mathit{E}}_{\mathit{T}}$=0.59\ifmmode\pm\else\textpm\fi{}0.02 eV is found. The electron-capture cross section is determined to be \ensuremath{\approxeq}(6.6\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ ${\mathrm{cm}}^{2}$. Thus, the controversy about the previously reported variations in \ensuremath{\Delta}E values is resolved. A comparison of \ensuremath{\Delta}E(0) with the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ energy position in GaAs and ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As shows that the energies are within 20 meV horizontally across the heterojunction, confirming a prediction of the ``internal-reference'' rule for the energy position of transition-metal levels in isoelectronic semiconductors.