Large tunable bandgaps in the InAs/AlAs strain-compensated short-period superlattices grown by molecular beam epitaxy

To explore the bandgap tunability in strain-compensated superlattices, we have grown a series of InAs/AlAs strain-compensated short-period superlattices (SPSs) with different period lengths by molecular beam epitaxy. Although the average indium composition of the InAs/AlAs SPS samples remains the same, the bandgaps of these SPSs measured by photoluminescence show a strong dependence on the period length, ranging from 1.41 to 1.01 eV as the period length varies from 4 ML to 10 ML. This fine control on the period length can extend the cutoff wavelength of this digital-alloy-like InAlAs (lattice matched to InP) material up to 1230 nm at room temperature. Multiple transitions are observed in Fourier transform infrared spectra, which agree well with the calculation and confirm the confinement in this structure. The strain effect in tuning the band structures and the band alignments is demonstrated, showing that longer period length together with smaller conduction band offset has led to the smaller effective bandgap of the InAs/AlAs SPS.