A. M. Hoang

Demonstration of shortwavelength infrared photodiodes based on type-II InAs/GaSb/AlSb superlattices

We demonstrate the feasibility of the InAs/GaSb/AlSb type-II superlattice photodiodes operating at the short wavelength infrared regime below 3 μm. An n-i-p type-II InAs/GaSb/AlSb photodiode was grown with a designed cut-off wavelength of 2 μm on a GaSb substrate. At 150 K, the photodiode exhibited a dark current density of 5.6 × 10−8 A/cm2 and a front-side-illuminated quantum efficiency of 40.3%, providing an associated shot noise detectivity of 1.0 × 1013 Jones. The uncooled photodiode showed a dark current density of 2.2 × 10−3 A/cm2 and a quantum efficiency of 41.5%, resulting in a detectivity of 1.7 × 1010 Jones.

InAs/InAs1−xSbx type-II superlattices for high performance long wavelength infrared detection

High performance long-wavelength infrared nBn photodetectors based on InAs/InAs1−xSbx type-II superlattices on GaSb substrate have been demonstrated. The photodetectors 50% cut-off wavelength was ∼10 μm at 77 K. The photodetector with a 6 μm-thick absorption region exhibited a peak responsivity of 4.47 A/W at 7.9 μm, corresponding to a quantum efficiency of 54% at −90 mV bias voltage under front-side illumination and without any anti-reflection coating. With an R × A of 119 Ω·cm2 and a dark current density of 4.4 × 10−4 A/cm2 under −90 mV applied bias at 77 K, the photodetector exhibited a specific detectivity of 2.8 × 1011 cm. Hz/W.

Elimination of surface leakage in gate controlled type-II InAs/GaSb mid-infrared photodetectors

The electrical performance of mid-infrared type-II superlattice M-barrier photodetectors is shown to be limited by surface leakage. By applying gate bias on the mesa sidewall surface, leakage current is significantly reduced. Qualitatively IV modeling shows diffusion-dominated behavior of dark current at temperatures greater than 120 K. At 110 K, the dark current of gated device is reduced by more than 2 orders of magnitude, reaching the measurement system noise floor. With a quantum efficiency of 48% in front side illumination configuration, a 4.7μm cut-off gated device attains a specific detectivity of 2.5 × 1014 cmHz1/2/W at 110 K, which is 3.6 times higher than in ungated devices.

High performance photodiodes based on InAs/InAsSb type-II superlattices for very long wavelength infrared detection

Very long wavelength infrared photodetectors based on InAs/InAsSb type-II superlattices are demonstrated on GaSb substrate. A heterostructure photodiode was grown with 50% cut-off wavelength of 14.6 μm. At 77 K, the photodiode exhibited a peak responsivity of 4.8 A/W, corresponding to a quantum efficiency of 46% at −300 mV bias voltage from front side illumination without antireflective coating. With the dark current density of 0.7 A/cm2, it provided a specific detectivity of 1.4 × 1010 Jones. The device performance was investigated as a function of operating temperature, revealing a very stable optical response and a background limited performance below 50 K.

Demonstration of high performance bias-selectable dual-band short-/mid-wavelength infrared photodetectors based on type-II InAs/GaSb/AlSb superlattices

High performance bias-selectable dual-band short-/mid-wavelength infrared photodetector based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm and 4 μm was demonstrated. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0 × 10−9 A/cm2 at −50 mV bias voltage, providing an associated shot noise detectivity of 3.0 × 1013 Jones. The mid-wavelength channel exhibited a quantum efficiency of 33% and a dark current density of 2.6 × 10−5 A/cm2 at 300 mV bias voltage, resulting in a detectivity of 4.0 × 1011 Jones. The spectral cross-talk between the two channels was also discussed for further optimization.

High Operability 1024

Electrical and radiometric characterization results of a high-operability1024 × 1024 long wavelength infrared type-II superlattice focal plane array are described. It demonstrates excellent quantum efficiency operability of 95.8% and 97.4% at operating temperatures of 81 K and 68 K, respectively. The external quantum efficiency is 81% without any antireflective coating. The dynamic range is 37 dB at 81 K and increases to 39 dB at 68 K operating temperature. The focal plane array has noise equivalent temperature difference as low as 27 mK and 19 mK at operating temperatures of 81 K and 68 K, respectively, using f/2 optics and an integration time of 0.13 ms.

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Dielectric passivation of long wavelength infrared type-II InAs/GaSb superlattice photodetectors with different active region doping profiles has been studied. SiO2 passivation was shown to be efficient as long as it was not put in direct contact with the highly doped superlattice. A hybrid graded doping profile combined with the shallow etch technique reduced the surface leakage current in SiO2 passivated devices by up to two orders of magnitude compared to the usual design. As a result, at 77 K the SiO2 passivated devices with 10.5 μm cutoff wavelength exhibit an R0A of 120 Ω cm2, RmaxA of 6000 Ω cm2, and a dark current level of 3.5×10−5 A cm−2 at −50 mV bias.

1024 Long Wavelength Type-II Superlattice Focal Plane Array

We propose a new approach in device architecture to realize bias-selectable three-color shortwave-midwave-longwave infrared photodetectors based on InAs/GaSb/AlSb type-II superlattices. The effect of conduction band off-set and different doping levels between two absorption layers are employed to control the turn-on voltage for individual channels. The optimization of these parameters leads to a successful separation of operation regimes; we demonstrate experimentally three-color photodiodes without using additional terminal contacts. As the applied bias voltage varies, the photodiodes exhibit sequentially the behavior of three different colors, corresponding to the bandgap of three absorbers. Well defined cut-offs and high quantum efficiency in each channel are achieved. Such all-in-one devices also provide the versatility of working as single or dual-band photodetectors at high operating temperature. With this design, by retaining the simplicity in device fabrication, this demonstration opens the prospect for three-color infrared imaging.

Surface leakage current reduction in long wavelength infrared type-II InAs/GaSb superlattice photodiodes

A high-performance short-wavelength infrared n-i-p photodiode based on InAs/InAs1−xSbx/AlAs1−xSbx type-II superlattices on GaSb substrate has been demonstrated. The device is designed to have a 50% cut-off wavelength of ∼1.8 μm at 300 K. The photodetector exhibited a room-temperature (300 K) peak responsivity of 0.47 A/W at 1.6 μm, corresponding to a quantum efficiency of 37% at zero bias under front-side illumination, without any anti-reflection coating. With an R × A of 285 Ω cm2 and a dark current density of 9.6 × 10−5 A/cm2 under −50 mV applied bias at 300 K, the photodiode exhibited a specific detectivity of 6.45 × 1010 cm Hz1/2/W. At 200 K, the photodiode exhibited a dark current density of 1.3 × 10−8 A/cm2 and a quantum efficiency of 36%, resulting in a detectivity of 5.66 × 1012 cm Hz1/2/W.

High performance bias-selectable three-color Short-wave/Mid-wave/Long-wave Infrared Photodetectors based on Type-II InAs/GaSb/AlSb superlattices

By using gating technique, surface leakage generated by SiO2 passivation in long-wavelength infrared type-II superlattice photodetector is suppressed, and different surface leakage mechanisms are disclosed. By reducing the SiO2 passivation layer thickness, the saturated gated bias is reduced to −4.5 V. At 77 K, dark current densities of gated devices are reduced by more than 2 orders of magnitude, with 3071 Ω cm2 differential-resistance-area product at −100 mV. With quantum efficiency of 50%, the 11μm 50% cut-off gated photodiode has a specific detectivity of 7 × 1011 Jones, and the detectivity stays above 2 × 1011 Jones from 0 to −500 mV operation bias.By using gating technique, surface leakage generated by SiO2 passivation in long-wavelength infrared type-II superlattice photodetector is suppressed, and different surface leakage mechanisms are disclosed. By reducing the SiO2 passivation layer thickness, the saturated gated bias is reduced to −4.5 V. At 77 K, dark current densities of gated devices are reduced by more than 2 orders of magnitude, with 3071 Ω cm2 differential-resistance-area product at −100 mV. With quantum efficiency of 50%, the 11μm 50% cut-off gated photodiode has a specific detectivity of 7 × 1011 Jones, and the detectivity stays above 2 × 1011 Jones from 0 to −500 mV operation bias.