Defect spectroscopy of MBE-grown GaAs0.51Sb0.49 pin infrared detectors on InP substrates

The deep level defect spectrum within GaAs0.51Sb0.49 photodiode absorber layers, grown by molecular beam epitaxy (MBE) and designed to operate at a wavelength of 1.55 μm, is revealed and characterized using deep level transient spectroscopy (DLTS) measurements. Two trap states were observed consistently and uniformly, with their trapping parameters quantified. Consistent with the high performance of these 1.55 μm photodetectors, total trap concentrations were very low, in the order of 1012 cm−3. The activation energies of the two detected states were found to be EC - 0.21 eV and EC - 0.40 eV. The near mid-gap position of the EC - 0.40 eV state implies a role as an efficient recombination-generation center and could be an important lifetime-limiting defect for MBE-grown GaAs0.51Sb0.49. A comparison was made with an inferior performing GaAs0.51Sb0.49 photodiode. DLTS measurements revealed the same defect states and spectra, implying that the sources of these defects are the same. However, trap concentrations were found to be substantially higher for the poorer-performing device. This correlation was further supported by comparing the minority carrier lifetimes of the two samples, measured using transient microwave reflectance (TMR). A significantly lower minority carrier lifetime was extracted for the lower performance device, consistent with higher trap concentrations. It was suggested that the near mid-gap trap detected at EC - 0.40 eV could be an important contributor to limiting the minority carrier lifetime within 1.55 μm GaAs0.51Sb0.49 photodetectors grown by MBE.