Benjamin Varberg Olson

Identification of dominant recombination mechanisms in narrow-bandgap InAs/InAsSb type-II superlattices and InAsSb alloys

Minority carrier lifetimes in doped and undoped mid-wave infrared InAs/InAsSb type-II superlattices (T2SLs) and InAsSb alloys were measured from 77–300u2009K. The lifetimes were analyzed using Shockley-Read-Hall (SRH), radiative, and Auger recombination, allowing the contributions of the various recombination mechanisms to be distinguished and the dominant mechanisms identified. For the T2SLs, SRH recombination is the dominant mechanism. Defect levels with energies of 130u2009meV and 70u2009meV are determined for the undoped and doped T2SLs, respectively. The alloy lifetimes are limited by radiative and Auger recombination through the entire temperature range, with SRH not making a significant contribution.

Cascaded Superlattice InAs/GaSb Light-Emitting Diodes for Operation in the Long-Wave Infrared

Superlattice InAs/GaSb light-emitting diodes with peak emission wavelength of 8.6 μm and output power approaching 190 μW at 77 K from a 120 × 120 μm2 mesa are demonstrated. Output power in excess of 600 μ.W was demonstrated from a 520 × 520 μm mesa at 1 A drive current and 50% duty cycle. Devices were grown by molecular beam epitaxy on lightly n-doped GaSb substrates and employed a 16-stage cascaded active region configuration to improve current efficiency and increase optical output. Emitting regions were coupled by semi-metallic tunnel junctions consisting of a p-GaSb layer and a thickness-graded InAs/GaSb superlattice stack.

Minority carrier lifetimes in very long-wave infrared InAs/GaInSb superlattices

Significantly improved carrier lifetimes in very-long wave infrared InAs/GaInSb superlattice (SL) absorbers are demonstrated by using time-resolved microwave reflectance (TMR) measurements. A nominal 47.0u2009A InAs/21.5u2009A Ga0.75In0.25Sb SL structure that produces an approximately 25u2009μm response at 10u2009K has a minority carrier lifetime of 140u2009±u200920u2009ns at 18u2009K, which is markedly long for SL absorber with such a narrow bandgap. This improvement is attributed to the strain-engineered ternary design. Such SL employs a shorter period with reduced gallium in order to achieve good optical absorption and epitaxial advantages, which ultimately leads to the improvements in the minority carrier lifetime by reducing Shockley–Read–Hall (SRH) defects. By analyzing the temperature-dependence of TMR decay data, the recombination mechanisms and trap states that currently limit the performance of this SL absorber have been identified. The results show a general decrease in the long-decay lifetime component, which is dominated by...

The role of InAs thickness on the material properties of InAs/GaSb superlattices

The epitaxial growth parameters optimized for mid-wavelength infrared (MWIR) InAs/GaSb superlattice (SL) growth are not directly applicable for long-wavelength infrared (LWIR) SL growth. We observed a two orders of magnitude drop in the spectral intensity of the measured photoresponse (PR) as the InAs layer thickness in the SL increases from 9 monolayers (MLs) to 16 MLs for a fixed GaSb layer thickness of 7 MLs. However, the theoretically calculated absorption strength decreases only by about a factor of two. So other factors affecting photoresponse, such as carrier mobility and lifetime, are likely responsible for the large drop in the PR of the LWIR SL in this sample set. In fact the measured Hall properties of MWIR and LWIR SLs are very different, with holes as the majority carriers in MWIR SLs and electrons as the majority carriers in LWIR SLs. Therefore we investigated the charge carrier density, carrier mobility, and carrier recombination dynamics in LWIR SL samples. Specifically we used temperature-dependent Hall effect and time-resolved pump-probe measurements to study the effect of adjusting several growth parameters on the background carrier concentrations and studied carrier lifetimes in LWIR SLs.

Effects of 4.5 MeV and 63 MeV proton irradiation on carrier lifetime of InAs/InAsSb type-II superlattices (Conference Presentation)

Type-II strained-layer superlattices (T2SLs) are receiving increased interest as mid-wave infrared (MWIR) and long-wave infrared detector absorbers due to their potential Auger suppression and ability to be integrated into complex device structures. Although T2SLs show promise for use as infrared detectors, further investigation into the effects of high energy particle radiation is necessary for space-based applications. In this presentation, the effects of both 4.5 MeV and 63 MeV proton radiation on the carrier lifetime of MWIR InAs/InAsSb T2SLs will be shown. The 63 MeV proton radiation study will focus on the carrier lifetime of MWIR InAs/InAsSb T2SL samples of varying donor density. These results reveal a Shockley-Read-Hall (SRH) lifetime associated with a radiation induced defect level, which is not dependent on the donor density of the T2SL. Using 4.5 MeV proton radiation, the dependence of carrier lifetime on relative trap density in MWIR T2SLs samples is studied by varying the particle fluence. A comparison of these two radiation studies shows similar lifetime effects that will be discussed in detail. These results give insight into the viability of Ga-free T2SLs for space applications.

Annealing effect on the long wavelength infrared InAs/GaSbsuperlattice materials

Annealing effect on the quality of long wavelength infrared (LWIR) InAs/GaSb superlattices (SLs) has been investigated using atomic force microscopy (AFM), photoconductivity, temperature dependent Hall, and time-resolved differential transmission measurements using an electronically delayed pump-probe technique. Quarters of a single SL wafer were annealed at 440, 480, and 515 °C, respectively for 30 minutes under a Sb-over pressure. Morphological qualities of the SL surface observed by AFM did not show any indication of improvement with annealing. However, the spectral intensity measured by photoconductivity showed an approximately 25 % improvement, while the band gap energy remained at ~107 meV for each anneal, The electron mobility was nearly unaffected by the 440 and 480 °C anneals, however showed the improvement with the 515°C anneal, where the mobility increased from ~4500 to 6300 cm2/Vs. The minority carrier lifetime measured at 77 K also showed the improvement with annealing, increasing from 12.0 to 15.4 nanoseconds. In addition to the longer lifetimes, the annealed samples had a larger radiative decay component than that of unannealed sample. Both the longer measured lifetime and the larger radiative decay component are consistent with the modest improvement in the quality of the annealed SL sample. Overall the qualities of LWIR SL materials can be benefit from a post growth annealing technique we applied.