Radiative recombination in surface-free n + /n - /n + GaAs homostructures

We show that the radiative efficiencies and lifetimes of photoexcited carriers in epitaxial GaAs may both be enhanced by three to four orders of magnitude by the preparation of thin n⁺, doped layers at the surface and substrate interfaces. Samples were prepared by organometallic vapor phase epitaxy with n^- region (∼10¹⁵ cm^-3) thicknesses of 3-10 μm and n⁺ regions Si doped to concentrations of 5×10¹⁸ cm^-3. Time-resolved luminescence in such structures (25-300 K), under both surface and bulk (near-band- edge) excitation conditions, reveals band-to-band-dominated recombination spectra, with carrier lifetimes ranging from a minimum of 150 ns at 50 K to 800 ns at room temperature. This is in sharp contrast to the subnanosecond lifetimes and poor raditive efficiencies typical in conventionally prepared, bulk or epitaxial GaAs, but is comparable to the best reported for high-purity LPE GaAs/Al_xGa_1-xAs double heterostructures.