Quantum Well Infrared Photodetectors Research Articles

Influence of Passivation Layers for Metal Grating-Based Quantum Well Infrared Photodetectors

To improve absorption of quantum well infrared photodetectors (QWIPs), a coupling layer with metallic grating is designed and fabricated above the quantum well. The metal grating is composed of 100 nm Au film on top, and a 20-nm Ti thin layer between the Au film and the sapphire substrate is coated as an adhesion/buffer layer. To protect the photodetector from oxidation and to decrease leakage, a SiO2 film is deposited by means of plasma-enhanced chemical vapor deposition. A value of about 800 nm is an optimized thickness for the SiO2 applied in the metallic grating-based mid-infrared QWIP. In addition, a QWIP passivation layer is studied experimentally. The results demonstrate that the contribution from the layer is positive for metal grating coupling with the quantum well. The closer the permittivity of the two dielectric layers (SiO2 and the passivation layers), and the closer the two transmission peaks, the greater the QWIP enhancement will be.

Structure and Process of Infrared Hot Electron Transistor Arrays

An infrared hot-electron transistor (IHET) 5 × 8 array with a common base configuration that allows two-terminal readout integration was investigated and fabricated for the first time. The IHET structure provides a maximum factor of six in improvement in the photocurrent to dark current ratio compared to the basic quantum well infrared photodetector (QWIP), and hence it improved the array S/N ratio by the same factor. The study also showed for the first time that there is no electrical cross-talk among individual detectors, even though they share the same emitter and base contacts. Thus, the IHET structure is compatible with existing electronic readout circuits for photoconductors in producing sensitive focal plane arrays.

Electromagnetic Modeling of Quantum Well Infrared Photodetectors

Rigorous electromagnetic field modeling is applied to calculate the quantum efficiency of various quantum well infrared photodetector (QWIP) geometries. We found quantitative agreement between theory and experiment for corrugated-QWIPs, grating-coupled QWIPs, and enhanced-QWIPs, and the model explains adequately the spectral lineshapes of the quantum grid infrared photodetectors. After establishing our theoretical approach, we used the model to optimize the detector structures for 12-micron pixel pitch focal plane arrays.

Detectivity enhancement in quantum well infrared photodetectors utilizing a photonic crystal slab resonator

We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.

Impact ionization in quantum well infrared photodetectors with different number of periods

This paper presents the detailed investigation of the photocurrent accompanied with impact ionization effect in In0.15Ga0.85As/GaAs multiple quantum well infrared photodetectors (QWIPs) with 10 and 50 periods. The sample with 50 periods exhibits remarkable enhancement at high electric field while a negative differential conductivity (NDC) phenomenon is observed in the sample with 10 periods. The enhancement at high electric field is attributed to impact ionization across the conduction-band-edge discontinuity between incident hot electrons and the electrons confined in the wells. The different behavior of these two samples indicates that the length of the multiplication region strongly affects the multiplication factor M. We also measured the photocurrent of GaAs/Al0.15Ga0.85As QWIPs, which do not show an obvious multiplication phenomenon. This is attributed to a different impact ionization coefficient α. A theoretical model of the multiplication factor M varying with impact ionization coefficient α, capture probability pc, and well number N is provided to clarify these phenomena and compared with experimental result.

40 K single-stage coaxial pulse tube cryocoolers

Several 40K single-stage coaxial high frequency pulse tube cryocoolers (PTCs) have been developed to provide reliable and low-noise cooling for GaAs/AlGaAs Quantum-Well infrared photodetectors (QWIPs). The inertance tubes together with the gas reservoir become the only phase shifter to guarantee the required long-term stability. The mixed regenerator consisting of three segments has been developed to enhance the overall regenerator performance. At present, the cooler prototype has achieved a no-load temperature of 29.7K and can typically provide 860mW cooling at 40K with 200W electric input power rejecting at 300K. The performance characteristics such as the temperature stability and ambient temperature adaptability are also presented.

Implementation of a semi-transparent mid-infrared quantum well infrared photodetector simultaneously as a beamsplitter and a reference detector

We demonstrate a dual purpose quantum well infrared photodetector (QWIP) useful in laser-based gas sensing systems. This photodetector functions simultaneously as a beamsplitter and a photodetector. By varying the incidence angle and light polarization, the QWIP has the ability to reflect, absorb, and transmit varying percentages of the incident mid-infrared light. At 45° incidence angle, ∼25% of a transverse magnetic polarized light is reflected, ∼16% is transmitted, and ∼59% is absorbed by the QWIP (at 80 K). The absorbed and transmitted signals are useful as reference signals for laser source monitoring and stabilizing. The reflected signal remains available as the primary beam.

Infrared photocurrent with one- and two-photon absorptions in a double-barrier quantum well system

We present a theoretical investigation of a double-barrier quantum-well infrared photodetector (QWIP) having two-color selectivity. The quantum well is placed between a pair of potential barriers in order to increase selectivity through modulation of the continuum states. This also leads to a potential decrease in the dark current. Calculations are carried in the effective-mass approximation using a single-electron hamiltonian. The approach used to obtain the photocurrent yields the observation of single as well as many-photon transitions in a unified manner, by naturally accounting for real and virtual processes through intermediate states that take part in the generation of photocurrent. The two-color selectivity of the calculated photocurrent spectra comes from both one- and two-photon transitions. The performance of the system studied is compared to the results for the isolated quantum well and the advantages of the double barrier are pointed out.

Investigation on the limit of weak infrared photodetection

We investigate the limit of weak infrared photodetection based on a systematic analysis of three main noise mechanisms, and point out the principles to achieve the ultimate performance. Two key issues should be addressed to realize ultra-sensitive infrared photodetection: suppression of background radiation, selection and optimization of photodetectors. We quantitatively studied the dependence of ultimate performance on the background temperature and emissivity. It is revealed that the background limited infrared performance detectivity for mid-infrared photodetection can be increased from the range of 1010 to 1011 cmHz1/2/W to 1015 cmHz1/2/W or even higher values, when the background radiation temperature decreases from the ambient to liquid nitrogen temperature. Furthermore, we investigate the feasibility of photoconductive infrared photodetectors for ultra-sensitive photodetection. Our simulations shows that ideal quantum well infrared photodetectors (QWIPs) can reach background limited infrared performance at feasible operation temperatures facing even very weak background radiation. For specific and quantitative analyses, QWIPs are used as the examples. However, the conclusions apply to a broader range of cases.

Voltage Tunable Dual-Band Quantum-Well Infrared Photodetector for Third-Generation Thermal Imaging

We investigate the theoretical calculations of the voltage tunable dual-band quantum-well infrared photodetector (QWIP) in the long and very long wavelength infrared range (LWIR and VLWIR). The detector consists of two serially connected GaAs/AlGaAs stacks which have spectral responses of 8.4- and 14- μm wavelengths, respectively. The peak responsivity wavelength of the stacks shifts from 8.4 to 14 μm as the bias voltage is increased.

Long wavelength infrared (LWIR) photodetection in a modulation doped thyristor

A modulation doped thyristor concept is described for LWIR photodetection based upon intersubband bound to continuum absorption. The intersubband absorption generates photocurrent from undoped quantum wells to modulation doped layers (MDL). Due to the lower dark current compared to conventional quantum well infrared photodetectors (QWIPs), the thyristor infrared detector operates with little or no cooling and with similar or better performance than QWIPs at low temperatures. The operating characteristics of absorption coefficient, quantum efficiency, responsivity, detectivity, infrared gain, and dark current are determined as a function of thyristor voltage and input power level in the range of 1 μW/cm 2.

Comparison of Quantum Dots-in-a-Double-Well and Quantum Dots-in-a-Well Focal Plane Arrays in the Long-Wave Infrared

Our previous research has reported on the development of the first generation of quantum dots-in-a-well (DWELL) focal plane arrays (FPAs), which are based on InAs quantum dots (QDs) embedded in an InGaAs well having GaAs barriers, which have demonstrated spectral tunability via an externally applied bias voltage. More recently, technologies in DWELL devices have been further advanced by embedding InAs QDs in InGaAs and GaAs double wells with AlGaAs barriers, leading to a less strained InAs/InGaAs/GaAs/AlGaAs heterostructure. These lower strain quantum dots-in-a-double-well devices exhibit lower dark current than the previous generation DWELL devices while still demonstrating spectral tunability. This paper compares two different configurations of double DWELL (DDWELL) FPAs to a previous generation DWELL detector and to a commercially available quantum well infrared photodetector (QWIP). All four devices are 320 × 256 pixel FPAs that have been fabricated and hybridized with an Indigo 9705 read-out integrated circuit. Radiometric characterization, average array responsivity, array uniformity and measured noise equivalent temperature difference for all four devices is computed and compared at 60 K. Overall, the DDWELL devices had lower noise equivalent temperature difference and higher uniformity than the first-generation DWELL devices, although the commercially available QWIP has demonstrated the best performance.

Quantum well infrared photodetectors: present and future

A review of the III-V Lab activities in the field of quantum well infrared photodetectors (QWIPs) is presented. We discuss the specific advantages of this type of detector and present the production facilities and status. A large section is dedicated to broadband QWIPs for space applications and to QWIPs on InP for mid-wavelength infrared detection. We review the progress of QWIP technology for the next generation (dual band, polarimetric, and multispectral) of thermal imagers. Finally, the state-of-the-art of very long wavelength QWIPs is discussed.

Tensile strained SiGe quantum well infrared photodetectors based on a light-hole ground state

We report the fabrication and thorough characterization of tensile strained p-type SiGe quantum well infrared photodetectors (QWIPs) grown on a Si0.74Ge0.26 pseudosubstrate. The QWIPs operate from a light-hole (LH) ground state and feature responsivity peaks in both the terahertz and mid-infrared regimes with responsivity values up to 3.7 mA/W, originating from LH–LH, LH–heavy-hole, and LH–split-off-band transitions.

Modelling of electronic transport in Quantum Well Infrared Photodetectors

Our interest is to model the electronic transport in Quantum Well Infrared Photodetectors (QWIPs). Standard modelling was based on self-consistent calculation of the non-uniform electric field with empirical description of the electron capture (Thibaudeau et al., 1996 [17]). Realistic empirical parameters had to be extracted from experiment, consequently purely numerical studies were not possible. Moreover, this approach allowed only a qualitative description of transport phenomena. In order to get rid of adjustable parameters, we have changed for a modelling based on the microscopic description of the transport (Jovanović et al., 2004 [11]). We have applied this modelling to the design of a variety of QWIPs. For example, excellent agreement with experimental dark current–voltage curves for different sizes of the barriers is demonstrated on a 8 μm detector over more than 6 orders of magnitude. The behaviour with respect to temperature on a wide range (30–200 K) is also well reproduced on this device as well as on a 17 μm detector. Those promising results confirm that this approach can give not only a good quantitative agreement but can also be a useful predictive tool.

Photonic crystal slab quantum well infrared photodetector

In this letter we present a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS). With the PCS it is possible to enhance the absorption efficiency by increasing photon lifetime in the detector active region. To understand the optical properties of the device we simulate the PCS photonic band structure, which differs significantly from a real two-dimensional photonic crystal. By fabricating a PCS-QWIP with 100x less quantum well doping, compared to a standard QWIP, we are able to see strong absorption enhancement and sharp resonance peaks up to temperatures of 170 K.

Dual-band quantum well infrared photodetectors with two ohmic contacts

Two-color quantum well infrared photodetectors (QWIPs) with two stacks of QW series have been grown by molecular beam epitaxy and processed into mesa structure devices with only two ohmic contacts by photolithography and wet chemical etching. By changing QWIP parameters, including barrier height, well width, doping level and period number, the total bias voltage can be distributed to the two stacks in such a way that the stacked structure will show different photoresponse characteristics. The photocurrent spectrum measurements demonstrate that sample 1 can work alternately between the two atmospheric windows of 3—5 μm and 8—12 μm by tuning the voltage, while sample 2 can photorespond simultaneously to the irradiation of the two atmospheric windows. In this paper, the physics behind the two-contact type of QWIP is discussed. The voltage tunability and the simultaneous photoresponse are attributed to the change of photoconductive gain with the bias voltage and the distribution of the total bias between the two series. We here focus the discussion on the voltage tunability of sample 1. Compared with the three-contact-per-pixel structure, two-contact-per-pixel structure can greatly facilitate the dual-band focal plane array (FPA) device fabrication and increase the FPA fill factor.

Optimization of Duty Ratio of Metallic Grating Arrays for Infrared Photodetectors

Influence of duty ratio of metallic gratings applied in quantum well infrared photodetector (QWIP) with detection ranging from 3 &#956m to 5 &#956m was studied in this paper. The influence on longer enhanced wavelength working at infrared waveband was investigated. A relationship between the duty ratio and the enhanced peak intensity is given. Some results can be applied to optimize the enhanced efficiency of the metallic gratings.

High speed QWIP FPAs on InP substrates

Quantum well infrared photodetector (QWIP) technology has allowed the realization of low cost staring focal plane arrays (FPAs). However, AlGaAs/(In)GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate and/or low background conditions. We extensively discuss the effect of sensor gain on the FPA performance under various operating conditions, and highlight the superiority of the InP/InGaAs material system with respect to AlGaAs/GaAs for high speed/low background thermal imaging applications. InP/InGaAs QWIPs, providing a bias adjustable gain in a wide range, offer the flexibility of adapting the FPA to strict operating conditions. We also present an experimental comparison of large format AlGaAs/GaAs and (strained) InP/InGaAs QWIP FPAs under different operating conditions. A 640 × 512 QWIP FPA constructed with the 40-well strained InP/In 0.48Ga 0.52As material system displays a cut-off wavelength of 9.7 μm ( λ p = 8.9 μm) with a BLIP temperature higher than 65 K ( f/2), and a peak quantum efficiency as high as 12% with a broad spectral response (Δ λ/ λ p = 17%). The conversion efficiency of the FPA pixels is as high as 20% under large bias (4 V) where the detectivity is reasonably high (∼3 × 10 10 cm Hz 1/2/W, f/2, 65 K). While providing a considerably higher quantum efficiency than the pixels of a similar AlGaAs/GaAs FPA, the InP/InGaAs QWIP provides similar NETD values with much shorter integration times and, being less sensitive to the read noise, successfully operates with sub-millisecond integration times. The results clearly demonstrate that InP based material systems display high potential for single- and dual-band QWIP FPAs by overcoming the limitations of the standard GaAs based QWIPs under high frame rate and/or low background conditions.

Large area III–V infrared focal planes

Jet Propulsion Laboratory is actively developing the III–V based infrared detector and focal plane arrays (FPAs) for remote sensing and imaging applications. Currently, we are working on Superlattice detectors, multi-band quantum well infrared photodetectors (QWIPs), and quantum dot infrared photodetector (QDIPs) technologies suitable for high pixel-pixel uniformity and high pixel operability large area imaging arrays. In this paper, we will discuss the demonstration of long-wavelength 1 K × 1 K QDIP FPA, 1 K × 1K QWIP FPA, the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP FPA, and demonstration of the first mid-wave and long-wave 1K × 1K superlattice FPA. In addition, we will discuss the advantages of III–V material system in the context of large format infrared FPAs.