Johnson Noise Limited Detectivity Research Articles

Broadband quantum cascade detectors with a cutoff wavelength of 20 μm

An InP-based photovoltaic quantum cascade detector with a cutoff wavelength of 20 μm is reported. A wave function tailored bound-to-miniband diagonal-transition active structure is proposed for the optical detection, effectively improving the photocurrent extraction efficiency and absorption strength, reducing the dark current leakage and consequently enhancing the responsivity and detectivity. The device demonstrates a broadband response of 16–20 μm over the operating temperature range. At 17.8 μm, a peak responsivity of 29.6 mA/W and a Johnson noise limited detectivity of 9 × 1010 Jones is obtained with a mesa of 200 μm × 200 μm, while maintaining a responsivity of 3.7 mA/W at 20 μm.

A Quantum Cascade Detector With Enhanced Extraction Efficiency Utilizing Localized Electric Field

An InGaAs/AlInAs quantum cascade detector (QCD) with localized electric field is proposed to produce a 40% higher extraction efficiency of photon-induced electrons when comparing with a conventional QCD. The localized electric field introduced by modulation doping extends the degrees of freedom in the regulation of electronic states in quantum wells, which has significant influence on the transport of electrons. The electric field can enhance the extraction efficiency by enlarging the transition matrix element related to the extraction process. The proposed mid-IR QCD demonstrates a peak responsivity of 156.9 mA/W and a Johnson noise limited detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9\times 10 ^{11}$ </tex-math></inline-formula> Jones at 80K.

Ultrahigh detectivity, high-speed and low-dark current AlGaN solar-blind heterojunction field-effect phototransistors realized using dual-float-photogating effect

High detectivity is essential for solar-blind deep-ultraviolet (DUV) light detection because the DUV signal is extremely weak in most applications. In this work, we report ultrahigh-detectivity AlGaN-based solar-blind heterojunction-field-effect phototransistors fabricated utilizing dual-float-photogating effect. The p + - Al 0.4 GaN layer and Al 0.4 GaN absorber layer deposited on the Al 0.6 GaN barrier serve as top pin-junction photogate, while the thin Al 0.4 GaN channel layer with a strong polarization field inside acts as virtual back photogate. Due to the effective depletion of the two-dimensional electron gas at the Al 0.6 Ga 0.4 N / Al 0.4 Ga 0.6 N heterointerface by the top photogate, the dark current was suppressed below 2 pA in the bias range of 0 to 10 V. A high photo-to-dark current ratio over 10 8 and an optical gain of 7.5 × 10 4 were demonstrated at a bias of 5 V. Theoretical analysis indicates that the optical gain can be attributed to the joint action of the floating top and back photogates on the channel current. As a result, a record high flicker noise (Johnson and shot noise) limited specific detectivity of 2.84 × 10 15 ( 2.91 × 10 17 ) cm Hz 0.5 W − 1 was obtained. Furthermore, high response speed at the microsecond level was also shown in the devices. This work provides a promising and feasible approach for high-sensitivity DUV detection.

Submonolayer quantum dot quantum cascade long-wave infrared photodetector grown on Ge substrate

A germanium (Ge) or germanium-on-silicon (Ge-on-Si) substrate is an attractive yet not well-studied platform for developing long-wave infrared photonics devices such as lasers and photodetectors. In this paper, we report a long-wave infrared quantum cascade photodetector grown on the Ge substrate with a submonolayer InAs/GaAs quantum dot as the infrared absorber. At 77 K under zero bias, the detector shows a differential-resistance area (R0A) product of 298.7 Ω·cm2. The normal-incident peak responsivity is 0.56 mA/W observed at 8.3 μm, corresponding to a Johnson noise limited detectivity of 1.5 × 108 cm·Hz1/2/W. In addition, the effect of the periodic stage number of active regions on device's performance is discussed in detail. The device characteristics presented in this work demonstrate the potential for monolithic integration of this quantum cascade detector with the Ge or Ge-on-Si substrate for large-scale, cost-effective sensing and imaging applications.

Growth and characterization of type-II superlattice photodiodes with cutoff wavelength of 12 μm on 4-in. wafer

High performance InAs/GaSb superlattices for long-wavelength infrared detection were grown on a 4-in. GaSb wafer using molecular beam epitaxy. The influence of the growth temperature, V/III BEP ratio on the surface morphology and microstructure was researched. The good uniformity of the surface roughness and crystallization at four location along the radial direction on the wafer was obtained by balancing the inner and outer growth temperature. The performance deviation of the four photodiodes fabricated using the superlattices from center to edge on the wafer was below 20% which revealed the uniformity of the superlattice growth and the fabrication process. The 50% cutoff wavelength was about 12 μm. The peak responsivity was 2.54 A/W corresponding to a quantum efficiency of 35.1% at 77 K. The zero bias differential resistance-area product (R0A) was 2.1 Ω cm2 due to the barrier structure design which restrains the diffusion dark current. The calculated Johnson noise limited detectivity was 5.75 × 1010 cm √Hz/W at 10 μm and 4.13 × 1010 cm √Hz/W at 14 μm.

Resonant-cavity infrared detector with five-quantum-well absorber and 34% external quantum efficiency at 4 μm.

We report resonant-cavity infrared detectors with 34% external quantum efficiency at room temperature at the resonant wavelength of 4.0 μm, even though the absorber consists of only five quantum wells with a total thickness of 50 nm. The full width at half maximum (FWHM) linewidth is 46 nm, and the peak absorption is enhanced by nearly a factor of 30 over that for a single pass through the absorber. In spite of an unfavorable Shockley-Read lifetime in the current material, the dark current density is at the level of state-of-the-art HgCdTe detectors as quantified by "Rule 07." The Johnson-noise limited detectivity (D*) at 21°C is 7 × 109 cm Hz½/W. We expect that future improvements in the device design and material quality will lead to higher quantum efficiency, as well as a significant reduction of the dark current density consistent with the very thin absorber.

Optimal absorber thickness in long-wave multiple-stage detector

The detectivity characteristics of interband cascade infrared type-II superlattice detectors for long-wave infrared detection (λcut-off = 8 μm at room temperature) are discussed. We present comparison of two superlattices: InAs/GaSb and InAs/InAsSb, assuming the characteristic parameters—absorption coefficients α and carrier lifetimes τ published in literature. Dependence of the Johnson-noise limited detectivity on the absorber thickness for a different number of stages is reported. Higher detectivity D* value can be achieved by increasing the carrier lifetime. However, for detectors based on type-II InAs/GaSb superlattice increasing the carrier lifetime up to 25 ns leads to a situation in which one stage is preferred, i.e. for detector with a single absorber, we obtain the highest detectivity value. In the case of InAs/InAsSb material, the situation is similar for τ ≥ 80 ns. We have shown that the optimal absorber thickness at which the highest detectivity values are obtained depends not only on the absorption coefficient α and the number of stages NS, but also on the carrier diffusion length L. According to a calculations, cascade detectors based on Ga-free material should have much higher optimal absorber thicknesses than materials based on InAs/GaSb.

Long wavelength infrared quantum cascade detector with a broadband response

A novel structure to achieve long wavelength infrared broadband detection ranging from 7.6–10.4 µm is proposed via quantum cascade detector. With a pair of identical coupled quantum wells separated by a thin barrier, acting as absorption regions, the relative linewidth (ΔE/E) of response can be dramatically broadened to 30.7%. Moreover, this structure introduces about 30% enhancement in blackbody responsivity. It is shown that the spectral shape can be tuned by the bias voltage effectively, while it is insensitive to the working temperature. The device can work at liquid nitrogen temperature with Johnson noise limited blackbody detectivity of 5.4 × 108 Jones.

Electrical gain in interband cascade infrared photodetectors

In order to achieve improved understanding and gain insights into the device operation of interband cascade infrared photodetectors (ICIPs) and ultimately to optimize the design, we present a comparative study of five long-wavelength (LW) ICIPs based on a type-II InAs/GaSb superlattice. This study shows how the device responsivity is affected by the individual absorber thicknesses and the number of cascade stages, through the impact of light attenuation. Additionally, this study further validates that the electrical gain universally exists in non-current-matched ICIPs. With multiple cascade stages to suppress noise, these LW ICIPs achieved superior device performance at high temperatures, in terms of Johnson-noise limited detectivities, compared to commercial MCT detectors. Furthermore, a theory is developed to quantitatively describe the electrical gain in ICIPs and our calculations are in good agreement with the experimental results. Based on the theory, the optimal number of stages for maximizing the device detectivity D* is identified with inclusion of the electrical gain. Our calculation shows that this optimal number of stages is relatively large in the presence of the gain and the maximized D* has a relatively weak dependence on the absorber thickness when it is sufficiently thin.

Current-matching versus non-current-matching in long wavelength interband cascade infrared photodetectors

We report on a comparative study of two sets of different long-wavelength (LW) interband cascade infrared photodetectors (ICIPs) based on a type-II InAs/GaSb superlattice. The devices in one set have a current-matched configuration while those in the other set are non-current-matched. It is shown that carrier transport in these LW ICIPs at high temperatures is diffusion limited and the diffusion length is estimated to be longer than or comparable to 0.5 μm at various temperatures. By comparing the two sets of devices, we demonstrate the necessity of current-matching to maximize utilization of absorbed photons for an optimal responsivity and the correlation of reduced responsivity with light attenuation in the optically deeper stages for non-current-matched ICIPs. However, the device performances for both sets are comparable in terms of detectivity. Electrical gain exceeding unity is observed, which is more significant in the last stage of non-current-matched ICIPs than in any other stages in order to obtain photocurrent continuity. The significant electrical gain enabled an appreciable responsivity in non-current-matched ICIPs and resulted in Johnson-noise limited detectivities as high as 2.4 × 108 Jones at 300 K, which substantially exceeds the reported value (e.g., 4.0 × 107 Jones) for commercial uncooled mercury cadmium telluride detectors.

Pushing Detection Wavelength Toward &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$1~\mu \text{m}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; by Type II InAs/GaAsSb Superlattices With AlSb Insertion Layers

We report on a short wavelength p-i-n detector using type II InAs/GaAsSb superlattices with AlSb insertion layers. The photoresponse is narrow-band like (δλ/λ=7.6%) and the wavelength at the response maximum is 1.08 μm at 77 K, the shortest wavelength reported until now. Insertion of AlSb thin layers not only helps reach such a short detection wavelength, but also reduces the dark current significantly. When a large positive bias voltage like +3 V is applied to the detector even at room temperature, the photoresponse is still clearly obtained, testifying a very small dark current of the device. The quantum efficiency of the device is 23% at 1.08 μm at 77 K, corresponding to the responsivity of 0.21 A/W. The resistance-area product at zero bias, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> A, is 1.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K and is 121 Ω · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 300K. The Johnson noise limited detectivity D* of the device is 1.1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Jones for the wavelength of 1.08 μm at 77 K.

High quantum efficiency mid-wavelength interband cascade infrared photodetectors with one and two stages

In this paper, we report on mid-wavelength infrared interband cascade photodetectors grown on InAs substrates. We studied the transport properties of the photon-generated carriers in the interband cascade structures by comparing two different detectors, a single stage detector and a two-stage cascade detector. The two-stage device showed quantum efficiency around 19.8% at room temperature, and clear optical response was measured even at a temperature of 323 K. The two detectors showed similar Johnson-noise limited detectivity. The peak detectivity of the one- and two-stage devices was measured to be 2.15 × 1014 cm·Hz1/02/W and 2.19 × 1014 cm·Hz1/02/W at 80 K, 1.21 × 109 cm·Hz1/02/W and 1.23 × 109 cm·Hz1/02/W at 300 K, respectively. The 300 K background limited infrared performance (BLIP) operation temperature is estimated to be over 140 K.

Narrow-Band Type II Superlattice Photodetector With Detection Wavelength Shorter Than &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$2~\mu \text{m}$ &lt;/tex-math&gt;&lt;/inline-formula&gt;

We demonstrate that type II InAs/GaSb superlattice photodetector can reach the detection wavelength shorter than $2~\mu \text{m}$ by inserting AlSb barriers. The detector exhibits a narrow-band photoresponse feature ( $\delta \lambda /\lambda =10.3\%$ ). At 77 K, the photoresponse maximum is at 1.84 $\mu \text{m}$ and the Johnson noise limited detectivity is $1.1\times 10^{13}$ Jones. We show that unlike a typical broad-band response feature using the interband transitions, for a p-i-n detector in the short wavelength range, a narrow-band response feature is the case, which is ascribed to the stronger absorption for the higher energy photons from the n region.

Room temperature quantum cascade detector operating at 4.3 μm

A strain-compensated InP-based InGaAs/InAlAs quantum cascade detector grown by solid source molecular beam epitaxy is demonstrated. The device operates at 4.3 μm up to room temperature (300 K) with a responsivity of 1.27 mA/W and a Johnson noise limited detectivity of 1.02 × 107 cm·Hz1/2/W. At 80 K, the responsivity and detectivity are 14.55 mA/W and 1.26 × 1010 cm·Hz1/2/W, respectively. According to the response range, this detector is much suitable for greenhouse gas detection.

Quantum dot quantum cascade infrared photodetector

We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 μm. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski–Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64 × 1011 and 4.83 × 106 Jones at zero bias were obtained at 80 K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging.

Long wavelength, very long wavelength and narrow-band long-/very-long wavelength two-color type-Ⅱ InAs/GaSb superlattice photodetectors

We have demonstrated a long wavelength (LW), a very-long wavelength (VLW) and a narrow-band two-color LW/VLW photodetectors using type-Ⅱ InAs/GaSb superlattice (SL) materials. For all the detection wavelengths, very high-quality type-Ⅱ InAs/GaSb SL materials have been grown by molecular beam epitaxy. For the LW device, at 77 K, the achieved 50% cutoff wavelength is 9.6 mm and the maximum response is at 7.7 mm with the responsivity of 3.2 A/W. For the VLW device, at 77 K, the 50% cutoff wavelength is 14.5 mm and the corresponding quantum efficiency is 14%. The Johnson noise limited detectivity D * is 4.3×109 cm Hz1/2 W-1 at 14.5 mm. For the first time, we demons- trate a narrow-band two-color detector using type-Ⅱ InAs/GaSb SL strctures. The LW/VLW two-color detector is a two-terminal device and the detection is achieved by changing the bias polarity. The device responds to the LW range when the bias voltage is smaller than 0 V while it works for the VLW range when the bias voltage is larger than 40 mV. Concretely, at 77 K, the 50% cutoff wavelength is 10 mm when the bias voltage is -0.1 V, and is 16 mm when the bias voltage is 40 mV. The achieved dl / l is 44% for the LW photoresponse and is 46% for the VLW photoresponse. The spectral crosstalk of the VLW band to the LW band is 9.9% while that of the LW band to the VLW band is 11.8%.

Effect of temperature on the current–voltage characteristics of GaAs/AlGaAs quantum cascade photodetectors

Transport of electrons within a quantum cascade photodetector structure takes place with the help of the scattering of electrons by phonons. By calculating scattering rates of the electrons mediated by longitudinal optical phonons (the dominant scattering mechanism), current–voltage characteristic of a quantum cascade photodetector is calculated. The results indicate that with the increase of bias voltage dark current increases rapidly, then the increase becomes slow at higher voltages, whilst photocurrent remains approximately constant with only slight variations in its magnitude. With the increase of temperature from 80K to 160K dark current increases by about two orders of magnitude while photocurrent varies slightly, so that at the illuminating power of 1mW/m2 photocurrent density increases in mean from 1.10×10−9A/cm2 at 80K to 1.14×10−9A/cm2 at 160K and then decreases to 1.03×10−9A/cm2 at 240K. Thus the responsivity of the detector varies only slightly with temperature. However owing to the decrease in the resistivity of the photodetector with the increase of temperature, Johnson noise limited detectivity decreases considerably.

19 μm quantum cascade infrared photodetectors

Two InP based InGaAs/InAlAs photovoltaic quantum cascade detectors operating at peak wavelengths of 18 μm and 19 μm using different electronic transport mechanisms are reported. A longitudinal optical phonon extraction stair combined with energy mini-steps are employed for electron transport, which suppresses the leakage current and results in high device resistance. Altogether, this quantum design leads to 15 K peak responsivity of 2.34 mA/W and Johnson noise limited detectivity of 1 × 1011 Jones at 18 μm.

High operating temperature interband cascade midwave infrared detector based on type-II InAs/GaSb strained layer superlattice

We report on an interband cascade mid-wave infrared (MWIR) detector based on type-II InAs/GaSb/AlSb strained layer superlattices (T2SL). The reported device has a seven-stage cascade region, each segment containing a MWIR absorber region, a graded T2SL transport region, and an interband tunneling region. Above room temperature spectral response was observed, with a cutoff wavelength of 7 μm at 420 K. Detailed radiometric measurements yielded a Johnson noise limited detectivity of 3.0 × 1011 cmHz1/2W−1 (8.9 × 108 cmHz1/2W−1) and a dark current density of 3.6 × 10−7 A/cm−2 (7.3 × 10−3 A/cm−2) near zero bias with a 100% cutoff wavelength of 5.2 μm and 6.2 μm at 77 K (295 K), respectively, with an estimated 36.2% QE.

Interband cascade infrared photodetectors with enhanced electron barriers and p-type superlattice absorbers

We present results on the optical and electrical performance of mid-infrared detectors based on interband-cascade structures. These devices include enhanced electron barriers, designed to suppress intraband-tunneling current between stages, and p-doped type-II InAs/GaSb superlattice absorbers. Within the sample set, we examined devices with different absorber thicknesses and doping levels. Carriers are extracted less efficiently in devices with longer absorbers, which is attributed to more band bending within the absorber due to electric charge accumulation. Also, devices with lower-doped (1 × 1017 cm−3) absorbers are found to have better optical and electrical performances than those with higher levels of doping (3 × 1017 cm−3). The overall performance of these devices was superior to previously reported results, with Johnson-noise limited detectivities, at 4.0 μm, as high as 6.0 × 1012 and 2.5 × 1011 Jones at 80 and 150 K, respectively.