T. F. Boggess

Time-resolved optical measurements of minority carrier recombination in a mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice

Measurements of carrier recombination rates using time-resolved differential transmission are reported for an unintentionally doped mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice. Measurements at 77u2009K yield minority carrier lifetimes of 3u2009μs and 9u2009μs for the InAsSb alloy and InAs/InAsSb superlattice, respectively. The un-optimized InAsSb-based materials also exhibit long lifetimes (>850u2009ns) at temperatures up to 250u2009K, indicating the potential use for these materials as mid-wave infrared photodetectors with improved performance over current type-II superlattice photodetectors at both cryogenic and near-ambient operating temperatures.

Auger recombination in narrow-gap semiconductor superlattices incorporating antimony

A comparison is performed between measured and calculated Auger recombination rates for four different narrow-gap superlattices based on the InAs/GaSb/AlSb material system. The structures are designed for optical or electrical injection for mid-infrared laser applications, with wavelengths ranging from 3.4 to 4.1 μm. The electronic band structures are computed employing an accurate 14-band restricted basis set (superlattice K⋅p) methodology that utilizes experimental information about the low-energy electronic structure of the bulk constituents. The superlattice band structures and their associated matrix elements are directly employed to compute Auger recombination rates. Varying amounts of Auger recombination suppression are displayed by the various superlattices as compared to bulk mid-infrared systems. The greatest disagreement between theory and experiment is shown for the structure predicted to have the most Auger suppression, suggesting the suppression is sensitive either to theoretical or growth u...

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.

Effects of layer thickness and alloy composition on carrier lifetimes in mid-wave infrared InAs/InAsSb superlattices

Measurements of carrier recombination rates using a time-resolved pump-probe technique are reported for mid-wave infrared InAs/InAs1−xSbx type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions, a 16u2009K band-gap of ≃235u2009±u200910u2009meV was achieved for all five unintentionally doped T2SLs. Carrier lifetimes were determined by fitting a rate equation model to the density dependent data. Minority carrier lifetimes as long as 10u2009μs were measured. On the other hand, the Auger rates for all the InAs/InAsSb T2SLs were significantly larger than those previously measured for InAs/GaSb T2SLs. The minority carrier and Auger lifetimes were observed to generally increase with increasing antimony content and decreasing layer thickness.

Spin relaxation in [110] and [001] InAs/GaSb superlattices

A 25 times enhancement of the electron spin lifetime is observed in a [110] InAs/GaSb superlattice relative to the corresponding [001] superlattice, an effect that is primarily attributed to suppression of native interface asymmetry.

Room-temperature electric-field controlled spin dynamics in (110)InAs quantum wells

We report the demonstration of room temperature gate control over the electron spin dynamics using the Rashba effect in a (110) InAs∕AlSb two-dimensional electron gas. Our calculations predict that the strong spin–orbit interaction in this system produces pseudomagnetic fields exceeding 1 T when only 140 mV is applied across a single quantum well. Using this large pseudomagnetic field, we demonstrate low-power spin manipulation on a picosecond time scale. Our findings are promising for the prospect of nonmagnetic low-power, high-speed spintronics.

All-optical measurement of vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices

Time-resolved differential transmission measurements were used to investigate vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices (T2SLs). By optically generating excess carriers near one end of the mid-wave T2SL and measuring the transit time to a thin, lower-bandgap T2SL at the other end, the time-of-flight of vertically diffusing carriers was measured. Through investigation of both unintentionally doped and p-type T2SLs, the vertical hole and electron diffusion coefficients were measured to be 0.04u2009±u20090.03u2009cm2/s and 4.7u2009±u20090.5u2009cm2/s, corresponding to vertical mobilities of 6u2009±u20095u2009cm2/Vs and 700u2009±u200980u2009cm2/Vs, respectively, at a temperature of 77u2009K.

Post growth annealing study on long wavelength infrared InAs/GaSb superlattices

The impact of post growth annealing on the electrical properties of a long wavelength infrared type-II superlattice (SL) was explored. Quarters of a single SL wafer were annealed at 440u2009°C, 480u2009°C, and 515u2009°C, respectively for 30 min. Changes in the electrical properties were followed using spectral photoconductivity, temperature dependent Hall effect, and time-resolved pump-probe measurements. The bandgap energy remained at ∼107 meV for each anneal, and the photoresponse spectra showed a 25% improvement. The carrier lifetime increased from 12 to ∼15 ns with annealing. The electron mobility was nearly constant for the 440u2009°C and 480u2009°C anneals, and increased from ∼4500 to 6300 cm2/Vs for the 515u2009°C anneal.

Comparison of tunnel junctions for cascaded InAs/GaSb superlattice light emitting diodes

Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. In this study, a variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. Here we used GaSb on the p-side of the junction, while varying materials on the n-side. The authors find Al0.20In0.80As0.73Sb0.27 tunnel junctions function best due to the low set of the conduction band; Ga0.75In0.25As0.23Sb0.77 also works well, though is more resistive due to a reduced set of the conduction band; and GaSb, while giving good hole confinement, results in a very resistive junction. Graded superlattice junctions can also work well, though they show sensitivity to doping levels, and present some challenges in growing strain-free.

InAs∕GaSb cascaded active region superlattice light emitting diodes for operation at 3.8μm

We report on the growth and characterization of InAs∕GaSb superlattice light emitting diodes (LEDs) operating in the midwave infrared at 3.8μm at 77K. Devices were grown by solid source molecular beam epitaxy on (100) GaSb substrates and were fabricated into 120×120μm2 mesa devices using wet etching. By employing an eight-stage cascaded active region design, output powers in excess of 1.5mW were achieved at 77K with 100mA peak drive current and a 50% duty cycle. Operating characteristics of the devices were examined from room temperature to 77K under quasi-dc excitation conditions.