Impurity and defect levels in beryllium-doped GaAs grown by molecular beam epitaxy

Abstract

Impurity and defect levels in Be-doped GaAs grown by molecular beam epitaxy have been studied by photoluminescence, Hall, and transient capacitance measurements. Epitaxial layers and n+-p diodes were grown at 602 °C using As4 molecular beams. The edge luminescence of our undoped and lightly Be-doped samples shows several defect-related transitions from 1.5049 to 1.5112 eV, in addition to the known donor- and acceptor-related excitonic transitions. Additional weak features occurring at energies from 50 to 100 meV below the band gap were also observed. Carbon was identified as the principal residual acceptor. Transitions involving Be were identified in the Be-doped layers and correlated with doping levels and binding energies from temperature-dependent Hall data. Deep level electron and hole traps with thermal activation energies ΔET ranging from 0.27 to 0.82 eV were detected in the GaAs layers. Trap concentrations were of the order of 1012–1014 cm−3 in layers with free-carrier concentrations ∼1016 cm−3. A hole trap with ΔET = 0.54 eV, consistently detected in our samples, is ascribed to Fe. A hole trap with ΔET = 0.90 eV which emerges after heat treatment may be related to As vacancies. The thermal capture cross section of the different traps have been estimated.