Optimizing residual carriers in undoped InAs/GaSb superlattices for high operating temperature mid-infrared detectors

The mid-infrared 21 Å InAs/24 Å GaSb superlattices (SLs) designed for the 4 μm cutoff wavelength were grown by molecular beam epitaxy at growth temperatures between 370 and 430 °C in order to reduce residual background carriers. The lowest density of 1.8×1011 cm−2 was obtained from the SLs grown at 400 °C. With increasing growth temperature, in-plane hole mobility decreased from 8740 to 1400 cm2/V s due to increased interfacial roughness, while the photoluminescence (PL) intensity increased due to a decrease in the number of nonstoichiometric nonradiative defects. Further reduction of carrier density to 1×1011 cm−2 was achieved by increasing barrier width. As GaSb layer width increases from 24 to 48 Å, the cutoff wavelength decreased from 4.1 to 3.4 μm, which is still in the mid-infrared detection window. More importantly, a dramatic improvement on the PL intensity and the full width at half maximum was achieved from the SL samples with the wider GaSb widths. All mid-infrared SL samples investigated in our studies were residually p-type.