The Study of MBE-Grown Type III Superlattices for Very Long Wavelength Infrared nBn Detectors

Potentials possessed by type-III superlattices in theory were not realized in practice, despite relatively comprehensive research efforts in the 1990s. Those efforts predict its several advantages relative to HgCdTe alloys, namely longer Auger lifetime, lower tunneling currents, sharper absorption onset, and more uniform and easier-to-control cutoff wavelength, especially in the very long wavelength infrared (VLWIR) region. In this thesis, T3SLs designed for VLWIR absorption were grown using molecular beam epitaxy (MBE) with precise layer thickness control. Various in-situ and ex-situ characterization methods were utilized to evaluate as-grown samples. The measured temperature-dependent infrared absorption spectra of the T3SL samples exhibit sharp and strong absorption onsets, which agree with our values calculated using the 14-band superlattice k.p method. However, T3SL’s significant interdiffusion under elevated temperatures during the annealing process after p-type ion implantation shifts the absorption edge to higher energies and even makes the superlattice characters disappear. This critical disadvantage makes T3SL unsuitable for photovoltaic photodetector applications. To fully exploit T3SL’s potential as an infrared detection material working in the VLWIR region and circumvent the need for p-type doping followed by high-temperature annealing, an nBn architecture based on HgTe/CdTe T3SL absorber and barrier that works in the VLWIR region is proposed for the first time. The T3SL barrier layer can be engineered to significantly reduce the valence band offset (VBO), an essential requirement for an efficient nBn structure. Additionally, a bias-selective two-color nBn with two absorbers working in VLWIR and long-wavelength infrared (LWIR) region is proposed. A detailed and integrated design is presented, and the dark current-voltage characteristics of the modeled device are evaluated.