InAsSb nBn Research Articles

Assessment of surface recombination in mid-wave infrared InAsSb nBn detectors using transient microwave reflectance

Investigation of surface recombination is an important area for infrared detectors as the demand for smaller pixels increases. In this study, we use transient microwave reflectance to characterize the minority carrier lifetime of InAsSb nBn structures under three conditions: As-Grown, blanket Barrier-Etched, and SU-8 Passivated blanket barrier-etched. A qualitative comparison of these three samples shows that the minority carrier lifetime decreases for the Barrier-Etched sample compared to the As-Grown sample, indicating that the minority carrier lifetime is sensitive to changes in the sample surface, specifically the introduction of surface states. We compare these samples quantitatively using a polynomial fit (A−1 + Bn + Cn2). We find for the As-Grown sample A = 1.22 ± 0.45 µs, B = 2.5 ± 0.2 × 10−12 cm3/s, and C = 5.004 ± 4.996 × 10−31 cm6/s, for the Barrier-Etched sample A = 1.17 ± 0.40 µs, B = 9.9 ± 0.2 × 10−12 cm3/s, and C = 9.502 ± 9.498 × 10−30 cm6/s, and for the Passivated sample A = 1.34 ± 0.45 µs, B = 5.3 ± 0.5 × 10−12 cm3/s, and C = 5.500 ± 4.500 × 10−33 cm6/s.

Frequency behavior of AlInAsSb nBn photodetectors and the development of an equivalent circuit model.

We report the frequency response of Al0.3InAsSb/Al0.7InAsSb nBn photodetectors. The 3-dB bandwidth of the devices varies from ∼ 150 MHz to ∼ 700 MHz with different device diameters and saturates with bias voltage immediately after the device turn on. A new equivalent circuit model is developed to explain the frequency behavior of nBn photodetectors. The simulated bandwidth based on the new equivalent circuit model agrees well with the bandwidth and the microwave scattering parameter measurements. The analysis reveals that the limiting factor of the bandwidth of the nBn photodetector is the large diffusion capacitance caused by the minority carrier lifetime and the device area. Additionally, the bandwidth of the nBn photodetector is barely affected by the photocurrent, which is found to be caused by the barrier structure in the nBn photodetector.

Al0.3InAsSb/Al0.7InAsSb Digital Alloy nBn Photodetectors

We report Al0.3InAsSb/Al0.7InAsSb digital alloy n-barrier-n (nBn) photodetectors that operate in the 2-μm wavelength window. The AlxIn1-xAsySb1-y digital alloy material system exhibits near-zero valence-band offset, which is beneficial for nBn photodetectors. At 300 K these Al0.3InAsSb/Al0.7InAsSb nBn photodetectors have achieved specific detectivities of 1.7 × 10 10 and 3.0 × 10 10 Jones under 2-μm and 1.8-μm illumination, respectively. The dark current density at -0.5 V bias decreases from 3.1 × 10 -3 A/cm 2 at 300 K to 1.6 × 10 -10 A/cm 2 at 120 K, where the dominant dark current component is tunneling. The area-dependence of key performance parameters show that for mesa diameter ≤ 250 μm, surface defects assume a dominant role in the total noise.

Surface leakage current reduction of InAsSb nBn MWIR HOT detector via hydrogen peroxide treatment

InAsSb nBn structure plays a key role in realizing high operating temperature (HOT) MWIR detectors. However, the AlAsSb layer, functioning as a barrier layer, can be rapidly oxidized during the pixel isolation process, forming undesirable oxides that can contribute to increase the surface leakage current. In this work, electrical and optical analysis were performed to investigate the role of the post-treatment process after pixel isolation step in reducing the oxidation and inhibiting the formation of unfavorable oxides closely related to the surface leakage currents. Our study shows that H2O2 post-treatment after the dry pixel isolation process can effectively reduce the barrier oxidation and suppress the formation of Sb2O5, greatly reducing the surface leakage current. Using the proposed post-treatment process, the dark current density of less than 1 × 10−6 A/cm2 was obtained at an applied bias of −0.3 V and 150 K, which is one order of magnitude lower than that of the InAsSb nBn device recently reported.

High-performance midwavelength infrared detectors based on InAsSb nBn design**Project supported by the National Key Technologies Research and Development Program of China (Grant No. 2018YFA0209104) and the Major Program of the National Natural Science Foundation of China (Grant No. 61790581).

we report nBn photodetectors based on InAs0.91Sb0.09 with a 100% cut-off wavelength of 4.75 μm at 300 K. The band of an nBn detector is similar to that of a standard pin detector, but there is special wide bandgap AlAs0.08Sb0.92 barrier layer in the nBn detector, in which the depletion region of nBn detector exists. The nBn design has many advantages, such as low dark current and high quantum efficiency, because the nBn design can suppress the generation–recombination (GR) current that is the main composition of standard pin detector dark current. The constant slope of the Arrhenius plot of J0–1/T indicates the absence of the generation–recombination dark current. We fabricate an nBn detector with a quantum efficiency (QE) maximum of ∼ 60% under −0.2-V bias voltage. The InAsSb nBn detectors may be a competitive candidate for midwavelength infrared detector.

A Thermoelectrically Cooled nBn Type‐II Superlattices InAs/InAsSb/B‐AlAsSb Mid‐Wave Infrared Detector

Herein, an nBn barrier mid‐wave infrared InAs/InAsSb (xSb = 0.4) type‐II superlattice (T2SL) detector operating in the thermoelectrical (TE) cooling condition is reported. AlAsSb (Sb‐composition, xSb ≥ 0.975) is shown not to introduce an additional barrier in the valence band in the analyzed temperature range (≥200 K) reached by four‐stage TE cooling in nBn barrier architectures with a T2SL InAs/InAsSb active layer. The dark current and photocurrent produced are analyzed in relation to the barrier and contact layer doping, with the Sb composition of the barrier indicating the optimal architecture. The results of the simulation are compared with the experimental results of the HgCdTe and InAsSb nBn barrier detectors. A detectivity of ≈1010 cmHz1/2 W−1 at 200 K is reported without an immersion lens (≈1011 cmHz1/2 W−1 is reported for an immersed detector).

Resonant cavity enhanced photodiodes on GaSb for the mid-wave infrared

We report the design, growth, processing, and characterization of resonant cavity enhanced photodiodes for the midwave infrared at ∼3.72 μm on GaSb. Using AlAsSb/GaSb mirrors, AlAsSb barrier and spacer layers and a thin 96 nm InAsSb absorber, we observed dark current and detectivity behavior superior to common InAsSb nBn detectors in the literature, with peak specific detectivity values of 8×1010 and 1×1010 cm Hz1/2 W−1 measured at 250 K and 300 K, respectively. In the same temperature range, the linewidth of the detector response was <44 nm and the quality factor ∼80. The peak quantum efficiency was >60% where the enhancement due to the resonant cavity was ∼20x. We estimate that the devices can operate close to, or slightly above, the background-limited infrared performance limit imposed on broadband detectors for a 300 K scene.

Spatial dependence of carrier localization in InAsSb/InSb digital alloy nBn detector

Recently we have demonstrated a novel method of extending the cut-off wavelength of InAsSb nBn detectors, by incorporating a series of monolayers of InSb, which we have termed a digital alloy. In recent work we have shown that while increasing temperature from 15 K to 40 K we observe a 14 meV blue shift of the photoluminescence peak energy and a decrease in minority carrier lifetime. We have hypothesized this effect is due to carrier localization caused by macro-scale fluctuations in layer thickness or alloy composition. Here we study the spatial variation of this effect over the surface of a sample, demonstrating significant variation with position. We discuss implications of this for the carrier localization hypothesis.

Monolithically Integrated InAsSb-Based nBnBn Heterostructure on GaAs for Infrared Detection

The high-operating temperature infrared photodetectors with multicolor function that are capable of monolithic integration are of increasing importance in developing the next generation of the mid-IR image sensors. Applications of these sensors include defense, medical diagnosis, environmental, and astronomical observations. We have investigated a novel InAsSb-based nBnBn heterostructure that combines a state-of-the-art InAsSb nBn detector with an InAsSb/GaSb heterojunction detector. At room temperature, the reduction in the dark current density of more than an order of magnitude was achieved compared to the previously investigated InAsSb/GaSb heterojunction detectors. Electrical characterization from cryogenic temperatures to room temperature confirmed that the nBnBn device was diffusion limited for the temperatures above 150 K. Optical measurements demonstrated that the nBnBn detector was sensitive in both the SWIR and MWIR wavelength range at room temperature. The specific detectivity ( D *) of the competed nBnBn devices was calculated to be ${\text{8.6}}\times {\text{10}}^{8}\,{{\text{cm}}\cdot {\text{Hz}}}^{1/ 2}{\text{W}}^{- 1}$ at 300 K and approximately ${\text{1.0}}\times {\text{10}}^{10}\,{{\text{cm}}\cdot {\text{Hz}}}^{1/ 2}{\text{W}}^{- 1}$ when cooled down to 200 K (with 0.3 V reverse bias and 1550-nm illumination). In addition, all the photodetector layers were grown monolithically on GaAs active layers using the interfacial misfit array growth mode. Our results, therefore, pave the way for the development of new active pixel designs for the monolithically integrated mid-IR imaging arrays.

Mid-wavelength infrared InAsSb/InSb nBn detector with extended cut-off wavelength

We extended the cut-off wavelength λc of bulk InAsSb nBn detectors to λc = 4.6 μm at T = 200 K by incorporating series of single InSb monolayer into InAsSb absorber. Detectors with 2 μm thick absorber showed a temperature independent quantum efficiency QEm ≈ 0.45 for back-side illumination without antireflection coating. The dark current density was jd = 5 × 10−6 A/cm2 at T = 150 K, and increased to jd = 2 × 10−3 A/cm2 at T = 200 K. At temperatures of T = 150 K and below, the demonstrated photodetectors operate in the background limited performance mode, with detectivity D*(λ) = 3–6 × 1011 cm Hz0.5/W for the background temperature of 300 K, and f/2 field of view.

InAsSb-based nBn photodetectors: lattice mismatched growth on GaAs and low-frequency noise performance

An InAsSb nBn detector structure was grown on both GaAs and native GaSb substrates. Temperature dependent dark current, spectral response, specific detectivity and noise spectral density measurements were then carried out. Shot-noise-limited figures of and were calculated (based upon the sum of dark current and background photocurrent) for the sample grown on GaAs and the sample grown on GaSb, respectively, at 200 K. Noise spectral density measurements revealed knee frequencies of between 124–337 Hz and ∼8 Hz, respectively. Significantly, these devices could support focal plane arrays capable of operating under thermoelectric cooling.

Room temperature performance of mid-wavelength infrared InAsSb nBn detectors

In this work we investigate the high temperature performance of mid-wavelength infrared InAsSb–AlAsSb nBn detectors with cut-off wavelengths near 4.5μm. The quantum efficiency of these devices is 35% without antireflection coatings and does not change with temperature in the 77–325K temperature range, indicating potential for room temperature operation. The device dark current stays diffusion limited in the 150–325K temperature range and becomes dominated by generation-recombination processes at lower temperatures. Detector detectivities of D*(λ)=1×109 (cmHz0.5/W) at T=300K and D*(λ)=5×109 (cmHz0.5/W) at T=250K, which is easily achievable with a one stage TE cooler.

Analysis of InAsSb nBn spectrally filtering photon-trapping structures.

We have numerically analyzed the electromagnetic and electrical characteristics of InAsSb nBn infrared detectors employing a photon-trapping (PT) structure realized with a periodic array of pyramids intended to provide broadband operation. The three-dimensional numerical simulation model was verified by comparing the simulated dark current and quantum efficiency to experimental data. Then, the power and flexibility of the nBn PT design was used to engineer spectrally filtering PT structures. That is, detectors that have a predetermined spectral response to be more sensitive in certain spectral ranges and less sensitive in others.

Room temperature performance of mid-wavelength infrared InAsSb nBn detectors

In this work, we investigate the high temperature performance of mid-wavelength infrared InAsSb-AlAsSb nBn detectors with cut-off wavelengths near 4.5 μm. The quantum efficiency of these devices is 35% without antireflection coatings and does not change with temperature in the 77–325 K temperature range, indicating potential for room temperature operation. The current generation of nBn detectors shows an increase of operational bias with temperature, which is attributed to a shift in the Fermi energy level in the absorber. Analysis of the device performance shows that operational bias and quantum efficiency of these detectors can be further improved. The device dark current stays diffusion limited in the 150 K–325 K temperature range and becomes dominated by generation-recombination processes at lower temperatures. Detector detectivities are D*(λ) = 1 × 109 (cm Hz0.5/W) at T = 300 K and D*(λ) = 5 × 109 (cm Hz0.5/W) at T = 250 K, which is easily achievable with a one stage TE cooler.