An investigation of magnesium in indium phosphide grown by molecular-beam epitaxy

Abstract

The role of magnesium as a p-type dopant in the growth of InP by molecular-beam epitaxy (MBE) has been investigated. The growth was performed at substrate temperatures of ≊500 °C under conditions which produced high-quality unintentionally doped InP with 77 K residual electron concentrations of ND−NA ≊2×1015 cm−3 and mobilities up to 42 500 cm2 V−1 s−1. InP grown in an elemental Mg flux under such ‘‘optimum’’ conditions has electrical properties which are comparable to those of the undoped material. Using low-temperature photoluminescence, the presence of electrically active shallow acceptors due to Mg and C has been detected in the ‘‘Mg-doped’’ samples, with Mg being the dominant impurity. Mg is also found to be the principal, electrically active shallow acceptor in undoped InP. The activation energies for Mg and C are 40.9 and 44.4±0.3 meV, respectively, in excellent agreement with previously published data for low-dose ion-implanted InP. Secondary electron microscopy studies on the Mg-doped InP show that the concentration of morphological defects increases as the Mg flux is increased, suggesting Mg is responsible for assisting the formation of defects. However, the increase in defect density does not appear to affect either the electrical or the optical properties of the semiconductor. The small concentration of Mg incorporated into InP from an elemental source makes it unsuitable as a p-type dopant in MBE growth under the condition discussed here.