Recombination and absorption in n-type gallium arsenide

This work recounts the efforts to completely characterize recombination, absorption and luminescence in n-type GaAs grown by metal-organic chemical vapor deposition (MOCVD) and doped with selenium to create electron concentrations, n$\sb{\rm o}$, from 1.3 $\times$ 10$\sp{17}$ cm$\sp{-3}$ to 3.8 $\times$ 10$\sp{18}$ cm$\sp{-3}$. To investigate recombination, photoluminescence (PL) decay was observed on double heterostructures (DH's) with thicknesses ranging from 0.25 to 10 $\mu$m. For n$\sb{\rm o}$ $<$ 10$\sp{18}$ cm$\sp{-3}$, recombination is dominated by radiative transitions with no evidence of Shockley-Read-Hall (SRH) recombination. For higher electron concentrations, samples show evidence of SRH recombination as reflected in the intensity dependence of PL decay. Even so, radiative recombination and photon recycling are important for all n$\sb{\rm o}$ studied. No evidence for Auger recombination is found, but an upper limit on the Auger coefficient is determined. Transmission measurements on thin-film DH's were used to deduce the near band edge absorption coefficient, $\alpha$(h$\nu$), over the photon energy range of 1.35 $\le$ h nu $\le$ 1.7 eV. A strong dependence of $\alpha$(h$\nu$) on the electron concentration was found as expected, based on previous work. Differences in the absorption tail, which increase with increasing n$\sb{\rm o}$, were attributed to compensation in the material studied previously. PL decay on thin-film membranes (for which the substrate is removed) yielded lifetimes greater than 1 $\mu$s for n$\sb{\rm o}$ = 1.3 $\times$ 10$\sp{17}$ cm$\sp{-3}$. This lifetime was enhanced three times over that observed with the substrate intact, because of enhanced photon recycling. By suppressing bulk recombination in this manner, it is found that the AlGaAs/GaAs interface recombination velocity, S, has an absolute upper limit of 25 cm/s. A more reasonable value is estimated as S $\le$ 11 cm/s. The absorption and recombination measurements are used to compute B, the radiative recombination coefficient, with self-consistent results. It is found that B decreases significantly with increasing n$\sb{\rm o}$. This is qualitatively in agreement with previous work, but the results differ quantitatively. This work describes completely the near band edge absorption properties and the recombination characteristics of high-quality n-GaAs grown by MOCVD. The results fill a void of understanding of intrinsic recombination in moderately doped n-GaAs and should be of value for the characterization and modeling of GaAs devices.