Low surface recombination velocity and contact resistance using p ⁺/p carbon-doped GaAs structures

Abstract

A reduction of the GaAs surface recombination velocity due to a heavily carbon-doped GaAs overlayer is reported. Metalorganic molecular beam epitaxy using trimethylgallium, triethylgallium, and elemental arsenic sources has been used to grow an epitaxial structure consisting of 1000 nm of p=1×10 17 cm-3 capped with 10 nm of p=1×1020 cm-3 GaAs. Time-resolved photoluminescence (PL) and PL excitation spectroscopy showed this p+/p structure to have a 3.2 ns carrier lifetime and strong band-edge PL emission, whose intensity was nearly constant over an excitation photon energy range of 1.5-3.3 eV. The same wafer with the p+ cap etched off exhibited a much shorter carrier lifetime and PL intensity that decreased exponentially with increasing photon energy, which is indicative of carrier losses to surface recombination. The specific contact resistivity of nonalloyed ohmic contacts to these heavily doped layers was observed to be in the mid 10-7 Ω cm2 range, independent of measurement temperature from 77 to 340 K, suggesting a tunneling contact due to the narrow surface depletion layer.