We report on the structural characterization of InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy. SL periodicity and overall structural quality were assessed by high-resolution X-ray diffraction and Raman spectroscopy. Spectroscopic ellipsometry was found to be sensitive to the (GaIn)Sb alloy composition.

Spectrally resolved measurements of the responsivity of infrared photodiodes based on InAs/(GaIn)Sb superlattices (SL) were performed in applied magnetic fields. For the field oriented parallel to the growth axis, interband Landau transitions related to both the center and the edge of the SL Brillouin zone in the growth direction were observed, in accordance with the parity selection rules that are expected for the type II system under consideration. For the field oriented perpendicular to the growth axis, the interband Landau resonances are broadened and the widening of the band gap is smaller.

Electric and optical properties of IR photodiodes based on InAs/(GaIn)Sb superlattices were investigations. Mesa diodes were fabricated with cut-off wavelengths ranging from 7.5 to 12 micrometers , showing 77 K detectivities between 1 X 1012 cmHz0.5/W and 5 X 1010 cmHz0.5/W, respectively. At least two leakage current mechanisms are observed in the reverse bias branch of the current-voltage characteristics. At high reverse bias band-to-band tunneling currents dominate. Close to zero voltage surface leakage currents become important. The leakage currents are studied with gate controlled mesa diodes, allowing depletion or inversion of the mesa side walls. In addition, the band-to- band tunneling currents are investigated by applying magnetic fields oriented parallel and perpendicular to the electric field across the p-n junction of the diode.

We report on the growth and characterization of InAs/(GaIn)Sb superlattices (SLs) as well as on the fabrication and testing of SL infrared (IR) photodiodes. InAs/Ga0.8In0.2Sb SLs with individual layer thicknesses of 12 and 10 monolayers, respectively, were grown by molecular-beam epitaxy either directly on GaSb substrates or on GaAs substrates using a strain-relaxed GaSb buffer layer. To achieve strain compensation, SL growth was performed with alternating InSb-like and GaAs-like interfaces. IR n(+)-on-p photodiodes employing a strain-optimized InAs/(GaIn)Sb SL as the active region were fabricated using standard III-V technology. SL photodiodes with cut-off wavelengths in the 7.5 to 8.5 mu m wavelength range showed at 77 K responsivities of 2 A/W and R(0)A products exceeding 10(3) Omega cm(2).

The optical and electrical properties of InAs/GaInSb superlattice mesa photodiodes with a cutoff wavelength around 8 µm are investigated. The influence of the surface potential at the mesa sidewalls on the device properties was studied by fabricating gate-controlled diodes. At least two mechanisms determining the dark current in the reverse bias region can be identified. At high reverse biases bulk bandto- band tunneling dominates while the current at low reverse biases is most likely governed by surface effects. Bulk interband tunneling is further investigated by applying magnetic fields B up to 7 T parallel and perpendicular to the electric field E across the p-n junction.

AlAs barriers embedded in GaAs were studied by spectroscopic ellipsometry and resonant Raman scattering. Heterostructures with AlAs barrier widths ranging from 2 to 30 nm were grown by molecular-beam epitaxy at growth temperatures between 410 and 660 °C. For layer widths below 10 nm the E1 and E1+Δ1 critical point resonance in the dielectric function of the AlAs was found to broaden and to be smeared out completely for a width of 2 nm. Resonant Raman scattering by the AlAs LO phonon reveals for layer widths ≤10 nm a considerable broadening of also the E0 interband transition in the AlAs. The magnitude of the critical point broadening and redistribution of oscillator strength, however, was found to be independent of the growth temperature and thus of the cation intermixing observed by Raman spectroscopy for growth temperatures ≥600 °C. Therefore, the observed critical point broadening is not caused by the formation of graded composition (AlGa)As barriers. Instead, the broadening of interband resonances is attributed to a spread of the carrier wave functions into the surrounding GaAs, which are not confined within the AlAs barrier for neither the E0 nor the E1 and E1+Δ1 interband transitions.