Aaron Gin

Type II InAs/GaSb superlattice photovoltaic detectors with cutoff wavelength approaching 32 μm

We report the most recent advance in the area of type II InAs/GaSb superlattice photovoltaic detectors that have cutoff wavelengths beyond 25 μm, with some at nearly 32 μm. The photodiodes with a heterosuperlattice junction showed Johnson noise limited peak detectivity of 1.05×1010 cm Hz1/2/W at 15 μm under zero bias, and peak responsivity of 3 A/W under −40 mV reverse bias at 34 K illuminated by ∼300 K background with a 2π field-of-view. The maximum operating temperature of these detectors ranges from 50 to 65 K. No detectable change in the blackbody response has been observed after 5–6 thermal cyclings, with temperature varying between 15 and 296 K in vacuum.

Advanced InAs/GaSb superlattice photovoltaic detectors for very long wavelength infrared applications

We report on the temperature dependence of the photoresponse of very long wavelength infrared type-II InAs/GaSb superlattice based photovoltaic detectors grown by molecular-beam epitaxy. The detectors had a 50% cutoff wavelength of 18.8 μm and a peak current responsivity of 4 A/W at 80 K. A peak detectivity of 4.5×1010 cm Hz1/2/W was achieved at 80 K at a reverse bias of 110 mV. The generation–recombination lifetime was 0.4 ns at 80 K. The cutoff wavelength increased very slowly with increasing temperature with a net shift from 20 to 80 K of only 1.2 μm.

Uncooled operation of type-II InAs∕GaSb superlattice photodiodes in the midwavelength infrared range

We report high performance uncooled midwavelength infrared photodiodes based on interface-engineered InAs∕GaSb superlattice. Two distinct superlattices were designed with a cutoff wavelength around 5μm for room temperature and 77 K. The device quantum efficiency reached more than 25% with responsivity around 1A∕W. Detectivity was measured around 109cmHz1∕2∕W at room temperature and 1.5×1013cmHz1∕2∕W at 77 K under zero bias. The devices were without antireflective coating. The device quantum efficiency stays at nearly the same level within this temperature range. Additionally, Wannier–Stark oscillations in the Zener tunneling current were observed up to room temperature.

Ammonium sulfide passivation of Type-II InAs/GaSb superlattice photodiodes

We report on the surface passivation of Type-II InAs/GaSb superlattice photodetectors using various ammonium sulfide solutions. Compared to unpassivated detectors, zero-bias resistance of treated 400 μm×400 μm devices with 8 μm cutoff wavelength was improved by over an order of magnitude to ∼20 kΩ at 80 K. Reverse-bias dark current density was reduced by approximately two orders of magnitude to less than 10 mA/cm2 at −2 V. Dark current modeling, which takes into account trap-assisted tunneling, indicates greater than 70 times reduction in bulk trap density for passivated detectors.

High quality type II InAs/GaSb superlattices with cutoff wavelength ∼3.7 μm using interface engineering

We report the most recent advance in the area of type II InAs/GaSb superlattices that have cutoff wavelength of ∼3.7 μm. With GaxIn1−x type interface engineering techniques, the mismatch between the superlattices and the GaSb (001) substrate has been reduced to <0.1%. There is no evidence of dislocations using the best examination tools of x-ray, atomic force microscopy, and transmission electron microscopy. The full width half maximum of the photoluminescence peak at 11 K was ∼4.5 meV using an Ar+ ion laser (514 nm) at fluent power of 140 mW. The integrated photoluminescence intensity was linearly dependent on the fluent laser power from 2.2 to 140 mW at 11 K. The temperature-dependent photoluminescence measurement revealed a characteristic temperature of one T1=245 K at sample temperatures below 160 K with fluent power of 70 mW, and T1=203 K for sample temperatures above 180 K with fluent power of 70 and 420 mW.

High performance Type II InAs/GaSb superlattices for mid, long, and very long wavelength infrared focal plane arrays

We present our most recent results and review our progress over the past few years regarding InAs/GaSb Type II superlattices for photovoltaic detectors and focal plane arrays. Empirical tight binding methods have been proven to be very effective and accurate in designing superlattices for various cutoff wavelengths from 3.7 μm up to 32 μm. Excellent agreement between theoretical calculations and experimental results has been obtained. High quality material growths were performed using an Intevac modular Gen II molecular beam epitaxy system. The material quality was characterized using x-ray, atomic force microscopy, transmission electron microscope and photoluminescence, etc. Detector performance confirmed high material electrical quality. Details of the demonstration of 256×256 long wavelength infrared focal plane arrays will be presented.

Type II InAs/GaSb superlattices for high-performance photodiodes and FPAs

The authors report the most recent progress in Type II InAs/GaSb superlattice materials and photovoltaic detectors developed for focal plane array applications with a cutoff wavelength of ~8 μm. No turn-on of tunneling current was observed even at a reverse bias of -3 V for a 3 μm thick p-i-n photodiodes. The thermally-limited zero bias detectivity under 300 K 2 π FOV was 2~3×1011 cm•Hz1/2/W at liquid nitrogen temperature, with a current responsivity of 2~3 A/W and a mean quantum efficiency of ~50%. Initial passivation using SiO2 has shown to decrease the dark current by ~30% at a reverse bias of -1 V. The same detector structure was used for focal plane arrays with silicon readout integrated circuit. Concept proof of imaging was demonstrated with a format of 256×256 at liquid nitrogen temperature.

Recent Advances in InAs/GaSb Superlattices for Very Long Wavelength Infrared Detection

New infrared (IR) detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous long and very long wavelength infrared imaging applications. One materials system has shown great theoretical and, more recently, experimental promise for these applications: InAs/InxGa1-xSb type-II superlattices. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection beyond 15 microns. The infrared properties of various compositions and designs of these type-II superlattices have been studied. The infrared photoresponse spectra are combined with quantum mechanical modeling of predicted absorption spectra to provide insight into the underlying physics behind the quantum sensing in these materials. Results for superlattice photodiodes with cut-off wavelengths as long as 25 microns will be presented.

Infrared detection from GaInAs/InP nanopillar arrays

We report on the photoresponse from large arrays of 40 nm radius nanopillars with sensitivity in the long-wavelength infrared regime. Using photoluminescence techniques, a peak wavelength blue shift of approximately 5 meV was observed at 30 K from GaInAs/InP nanopillar structures, indicating carrier confinement effects. Responsivity measurements at 30 K indicated peak wavelength response at about 8 µm with responsivity of 420 mA W−1 at −2 V bias. We have also measured the noise and estimated the peak detectivity to be 3 × 108 cm Hz1/2 W−1 at 1 V reverse bias and 30 K. A maximum internal quantum efficiency of 4.5% was derived from experiment. Both the photo and the dark transport have been successfully modelled as processes that involve direct and indirect field-assisted tunnelling as well as thermionic emission. The best agreement with experiment was obtained when allowances were made for the non-uniformity of barrier widths and electric field heating of carriers above the lattice temperature.

Negative luminescence of long-wavelength InAs∕GaSb superlattice photodiodes

The electrically pumped emission behavior of binary type-II InAs∕GaSb superlattice photodiodes has been studied in the spectral range between 8μm and 13μm. With a radiometric calibration of the experimental setup, the internal and external quantum efficiency has been determined in the temperature range between 80K and 300K for both, the negative and positive luminescence. The negative luminescence efficiency approaches values as high as 35% without antireflection coating. The temperature dependence of the internal quantum efficiency near zero-bias voltage allows for the determination of the electron-hole-electron Auger recombination coefficient of Γn=1×1024cm6s−1.