Yajun Wei

Very high quantum efficiency in type-II InAs∕GaSb superlattice photodiode with cutoff of 12μm

The authors report the dependence of the quantum efficiency on device thickness of type-II InAs∕GaSb superlattice photodetectors with a cutoff wavelength around 12μm. The quantum efficiency and responsivity show a clear delineation in comparison to the device thickness. An external single-pass quantum efficiency of 54% is obtained for a 12μm cutoff wavelength photodiodes with a π-region thickness of 6.0μm. The R0A value is kept stable for the range of structure thicknesses allowing for a specific detectivity (2.2×1011cmHz∕W).

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.

Near bulk-limited R0A of long-wavelength infrared type-II InAs∕GaSb superlattice photodiodes with polyimide surface passivation

Effective surface passivation of type-II InAs∕GaSb superlattice photodiodes with cutoff wavelengths in the long-wavelength infrared is presented. A stable passivation layer, the electrical properties of which do not change as a function of the ambient environment nor time, has been prepared by a solvent-based surface preparation, vacuum desorption, and the application of an insulating polyimide layer. Passivated photodiodes, with dimensions ranging from 400×400to25×25μm2, with a cutoff wavelength of ∼11μm, exhibited near bulk-limited R0A values of ∼12Ωcm2, surface resistivities in excess of 104Ωcm, and very uniform current-voltage behavior at 77K.

Passivation of type-II InAs∕GaSb double heterostructure

Focal plane array fabrication requires a well passivated material that is resistant to aggressive processes. The authors report on the ability of type-II InAs∕GaSb superlattice heterodiodes to be more resilient than homojunctions diodes in improving sidewall resistivity through the use of various passivation techniques. The heterostructure consisting of two wide band gap (5μm) superlattice contacts and a low band gap active region (11μm) exhibits an R0A averaging of 13Ωcm2. The devices passivated with SiO2, Na2S and SiO2 or polyimide did not degrade compared to the unpassivated sample and the resistivity of the sidewalls increased to 47kΩcm.

Capacitance-voltage investigation of high-purity InAs∕GaSb superlattice photodiodes

The residual carrier backgrounds of binary type-II InAs∕GaSb superlattice photodiodes with cutoff wavelengths around 5μm have been studied in the temperature range between 20 and 200K. By applying a capacitance-voltage measurement technique, a residual background concentration below 1015cm−3 has been found. At temperatures below 100K carrier freeze-out is observed with a thermal activation energy of 4.5meV, leading to net carrier concentrations at 77K in the mid 1014cm−3.

High-performance type-II InAs/GaSb superlattice photodiodes with cutoff wavelength around 7 μm

We report the most recent result in the area of type-II InAs/GaSb superlattice photodiodes that have a cutoff wavelength around 7 μm at 77 K. Superlattice with a period of 40 A lattice matched to GaSb was realized using GaxIn1−x type interface engineering technique. Compared with significantly longer period superlattices, we have reduced the dark current density under reverse bias dramatically. For a 3 μm thick structure, using sulfide-based passivation, the dark current density reached 2.6×10−5A∕cm2 at −3 V reverse bias at 77 K. At this temperature the photodiodes have R0A of 9300Ωcm2 and a thermally limited zero bias detectivity of 1×1012cmHz1∕2∕W. The 90%–10% cutoff energy width was only 16.5 meV. The devices did not show significant dark current change at 77 K after three months storage in the atmosphere.

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.