Molecular Beam Epitaxy growth and characterization of silicon – Doped InAs dot in a well quantum dot infrared photo detector (DWELL-QDIP)

We report the growth by Molecular Beam Epitaxy (MBE), fabrication and characterization of silicon doped 20 layer InAs dot in a well quantum dot infrared photo detector (DWELL-QDIP) device structures. Two structures with InAs dots of vertical heights of 50 Å and 40 Å were compared. A 2–8 μm band normal incidence photo response of the detector with polarization and bias dependence was obtained at 77 K. The specific peak detectivity D1 be 0.8 × 10⁹ Jones for one of the detectors.     

The effect of metal dispersion on the resonance of antennas at infrared frequencies

In this paper the optical parameters at infrared frequencies of metallic thin films were obtained experimentally using a variable angle spectroscopic ellipsometer and used to simulate numerically the frequency response of antennas and antenna-coupled detectors at infrared frequencies (5–15 μm). The simulation results agree with previously published data and practical guidelines are presented for the design and fabrication of dipole and bowtie antennas at infrared frequencies.     

Device-level vacuum packaged uncooled microbolometer on a polyimide substrate

Uncooled infrared detectors (IR) on a polyimide substrate have been demonstrated where amorphous silicon (a-Si) was used as the thermometer material. New concepts in uncooled microbolometers were implemented during the design and fabrication, such as the integration of a germanium long-pass optical filter with the device-level vacuum package and a double layer absorber structure. Polyimide was used for this preliminary work towards vacuum-packaged flexible microbolometers. The detectors were fabricated utilizing a carrier wafer and low adhesion strength release layer to hold the flexible polyimide substrate during fabrication in order to increase the release yield. The IR detectors showed a maximum detectivity of 4.54 × 10⁶ cm Hz^1/2/W at a 4 Hz chopper frequency and a minimum noise equivalent power (NEP) of 7.72 × 10⁻¹⁰ W/Hz^1/2 at a biasing power of 5.71 pW measured over the infrared wavelength range of 8–14 μm for a 35 μm × 35 μm detector. These values are comparable to other flexible microbolometers with device-level vacuum packaging which are found in literature.     

Complementary barrier infrared detector (CBIRD) with double tunnel junction contact and quantum dot barrier infrared detector (QD-BIRD)

The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from ∼4.2 μm to 6 μm, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.     

Quantum dot nanostructures for multi-band infrared detection

A dual-band (two-color) tunneling-quantum dot infrared photodetector (T-QDIP) structure, which provides wavelength selectivity using bias voltage polarity, is reported. In this T-QDIP, photoexcitation takes place in InGaAs QDs and the excited carriers tunnel through an AlGaAs/InGaAs/AlGaAs double-barrier by means of resonant tunneling when the bias voltage required to line up the QD excited state and the double-barrier state is applied. Two double-barriers incorporated on the top and bottom sides of the QDs provide tunneling conditions for the second and the first excited state in the QDs (one double-barrier for each QD excited state) under forward and reverse bias, respectively. This field dependent tunneling for excited carriers in the T-QDIP is the basis for the operating wavelength selection. Experimental results showed that the T-QDIP exhibits three response peaks at ～4.5 (or 4.9), 9.5, and 16.9 μm and selection of either the 9.5 or the 16.9 μm peak is obtained by the bias polarity. The peak detectivity (at 9.5 and 16.9 μm) of this detector is in the range of 1.0–6.0 × 10¹² Jones at 50 K. This detector does not provide a zero spectral crosstalk due to the peak at 4.5 μm not being bias-selectable. To overcome this, a quantum dot super-lattice infrared photodetector (SL-QDIP), which provides complete bias-selectability of the response peaks, is presented. The active region consists of two quantum dot super-lattices separated by a graded barrier, enabling photocurrent generation only in one super-lattice for a given bias polarity. According to theoretical predictions, a combined response due to three peaks at 2.9, 3.7, and 4.2 μm is expected for reverse bias, while a combined response of three peaks at 5.1, 7.8, and 10.5 μm is expected for forward bias.     

Pump tuned wide tunable noncritically phase-matched ZnGeP2 narrow line width optical parametric oscillator

A line tunable singly resonant noncritically phase matched narrow band width ZnGeP₂ (ZGP) optical parametric oscillator pumped by the output idler radiation from a KTA OPO based on a 20 mm long KTA crystal pumped from a Q-switched Gaussian shaped Nd:YAG laser beam with a grating having grooves density 85 lines/mm has been demonstrated in the spectral ranges of 3–7 μm. The measured threshold of oscillation energy was 10 μJ. The conversion efficiency was 20.5% and slope efficiency of the ZGP OPO was 20% using a 23 mm long ZGP crystal at 26 mm cavity length. Line width of the generated infrared radiation from ZGP OPO was 37–60 nm.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

Study of resonant modes in a 700 nm pitch macroporous silicon photonic crystal

In this study the modes produced by a defect inserted in a macroporous silicon (MP) photonic crystal (PC) have been studied theoretical and experimentally. In particular, the transmitted and reflected spectra have been analyzed for variations in the defect’s length and width. The performed simulations show that the resonant frequency is more easily adjusted for the fabricated samples by length tuning rather than width. The optimum resonance peak results when centered in the PC bandgap. The changes in the defect geometry result in small variations of the optical response of the PC. The resonance frequency is most sensitive to length variations, while the mode linewidth shows greater change with the defect width variation. Several MPS photonic crystals were fabricated by the electrochemical etching (EE) process with optical response in the range of 5.8 μm to 6.5 μm. Results of the characterization are in good agreement with simulations. Further samples were fabricated consisting of ordered modulated pores with a pitch of 700 nm. This allowed to reduce the vertical periodicity and therefore to have the optical response in the range of 4.4 μm to 4.8 μm. To our knowledge, modes working in this range of wavelengths have not been previously reported in 3-d MPS structures. Experimental results match with simulations, showing a linear relationship between the defect’s length and working frequency inside the bandgap. We demonstrate the possibility of tailoring the resonance peak in both ranges of wavelengths, where the principal absorption lines of different gases in the mid infrared are placed. This makes these structures very promising for their application to compact gas sensors.     

Operating temperature and the responsivity of split-off band detectors

A GaAs/AlGaAs heterojunction is used as a spin-split-off band IR detector operating at or around room temperature. This detector structure followed a similar layer architecture to the quantum well IR photo detectors (QWIP) and Heterojunction Interfacial Work function Internal Photoemission (HEIWIP) detectors. Compared to QWIPs, the emitter layer thickness is increased to avoid confinement. Unlike either the QWIPs or HEIWIPs, these detectors will have two energy gaps (barriers) to obtain the wavelength threshold which could be used to design detectors either for optimum operating temperature or optimum responsivity. The free carrier energy gap is determined by the Al fraction and the spin-split-off transition energy provides another handle on controlling the effective threshold of the detector. Unlike QWIPs, these will also detect normal incidence radiation. A preliminary detector showed a peak responsivity of 0.29 mA/W at 2.5 μm at room temperature.     

Identification of the photoluminescence response in the frequency domain modulated infrared radiometry signal of ZnTe:Cr bulk crystal

In this work we investigated the photoluminescence response in the frequency domain modulated infrared radiometry signal observed of ZnTe:Cr bulk crystal. In mid-infrared range, three characteristic phenomena are observed in ZnTe:Cr crystal: absorption and emission of IR photons (2–3 μm) and the free carrier absorption. This implies that the modulated infrared radiometry signal yields information about the effective infrared absorption coefficient (photothermal response) as well about the recombination lifetime of carriers related with the infrared photoluminescence emission. In this paper, the frequency equivalence of the two-term independent exponential photoluminescence decay model in order to explain the measured frequency characteristics is proposed. The measured recombination lifetimes (2.3 μs for two exponential decay model and 1.5 μs for one exponential decay model) are in good agreement with the values given by other authors (about 2.5–3.0 μs). Moreover, we found that the photothermal response is uncorrelated with the photoluminescence one, in contrast, to the photocarrier response.     

Spectral broadening and electron–photon coupling in III–V infrared detectors of low dimensional quantum confined system

Present work explores the mid-IR photodetection mechanism in III–V quantum confined system in twofold ways. Firstly, it models the extent of spectral linewidth broadening of photo-detector. Secondly, it investigates whether a strong perturbation of light can modulate the electronic bandstructure. Photo-absorption mechanism in the detector correlated to reduced carrier lifetime in ground state leading to homogeneous spectral widening is calculated. Besides, contribution of non-uniform size and composition of quantum dots towards spectral broadening is modeled in order to get the envelop of inhomogeneously broadened photocurrent spectrum. Our model generates photocurrent spectrum with 1.4 μm broadening centered at 3.5 μm at 77 K for a DWELL-IP, which agrees with the experimental result. The calculated photocurrent spectral width of 1.3 μm for GaAs/AlGaAs Quantum Well (QW) centered at 8.31 μm at 77 K also supports experimental data. In addition, our calculation reveals the emergence of a broad resonant peak in the spectrum of QW-IP in far infrared region (20–50 μm) as the photon volume density increases up to 0.1% of carrier density inside the active region. We introduce a hybrid density-of-states for strongly coupled electron–photon system to explain both mid and far IR peak.     

High energy femtosecond OPA pumped by 1030 nm Yb:KGW laser.

We present a traveling-wave-type optical parametric amplifier (OPA) pumped at 1.03 μm by a Yb:KGW laser that produces tunable high-energy pulses of 6.5–4 μJ in the mid-infrared (mid-IR) region from 3.6 to 7 μm. Pumping with negatively chirped pulses generates nearly transform-limited (TL) mid-IR pulses of 300–330 fs length. Pumping with TL pulses of 200 fs not only decreases the output energy by a factor of 1.5, but also decreases the mid-IR pulse-length to 160 fs after additional compression. The compact and simple OPA setup is ideal for femtosecond infrared experiments in the fingerprint region.     

Concept of infrared photodetector based on graphene–graphene nanoribbon structure

We study the mechanisms of photoconductivity in graphene layer–graphene nanoribbon–graphene layer (GL–GNR–GL) structures with the i-type gapless GL layers as sensitive elements and I-type GNRs as barrier elements. The effects of both an increase in the electron and hole densities under infrared illumination and the electron and hole heating and cooling in GLs are considered. The device model for a GL–GNR–GL photodiode is developed. Using this model, the dark current, photocurrent, and responsivity are calculated as functions of the structure parameters, temperature, and the photon energy. The transition from heating of the electron–hole plasma in GLs to its cooling by changing the incident photon energy can result in the change of the photoconductivity sign from positive to negative. It is demonstrated that GL–GNR–GL photodiodes can be used in effective infrared and terahertz detectors operating at room temperature. The change in the photoconductivity sign can be used for the discrimination of the incident radiation with the wavelength 2–3 μm and 8–12 μm.     

Intersubband transitions in quantum well mid-infrared photodetectors

A study of intersubband transitions in quantum well infrared detectors working at high temperatures has been reported. This study allows a greater tunability in the device designs, with the ability to control the peak wavelength, the absorption coefficient, the dark current, the quantum efficiency and the detectivity of the modeled structure operating around 3.3 μm wavelength. The detection energy and absorption coefficient dependences with an applied electric field are given. Then, the electro-optic performances of the modeled mid-infrared detector are estimated, the dark current dependence with the applied voltage and temperature as well as the quantum efficiency and the detectivity are investigated and discussed. High detectivities were found at high temperatures revealing the good performances of the designed photodetector, especially at 3.3 μm wavelength.     

InAs/GaSb superlattice infrared detectors

Future heterojunction InAs/GaSb superlattice (SL) detector devices in the long-wavelength infrared regime (LWIR, 8–12 μm) require an accurate bandstructure model and a successful surface passivation. In this study, we have validated the superlattice empirical pseudopotential method developed by Dente and Tilton over a wide range of bandgap energies. Furthermore, dark current data for a novel dielectric surface passivation for LWIR devices is presented. Next, we present a technique for high-resolution, full-wafer mapping of etch pit densities on commercial (1 0 0) GaSb substrates, which allows to study the local correlation between threading dislocations in the substrate and the electro-optical pixel performance. Finally, recent performance data for 384 × 288 dual-color InAs/GaSb superlattice imagers for the mid-wavelength infrared (MWR, 3–5 μm) is given.     

Vertical coupling characteristics between hybrid plasmonic slot waveguide and Si waveguide

For development of complementary metal–oxide–semiconductor (CMOS)-compatible integrated optical circuits, vertical directional coupling between a hybrid plasmonic slot waveguide and a Si waveguide is theoretically investigated in detail. To determine the vertical separation gap and efficient coupling length, we investigate the characteristics of the even and odd supermodes at a wavelength of 1.55 μm. The vertical coupler transfers 90% of the power carried by the Si waveguide to the hybrid plasmonic slot waveguide after normalizing to reference waveguides when the gap is 60 nm and the coupling length is 2.6 μm. Because of the lossy hybrid guided mode in the plasmonic waveguide, the transmitted power exhibits damped sinusoidal behavior depending on the overlapping length. The proposed vertical coupler shows more efficient light coupling between a dielectric and plasmonic waveguide in comparison to the other types of hybrid coupler, and can be exploited further for on-chip integrated opto-electronic circuits.     

Distinction investigation of InGaAs photodetectors cutoff at 2.9 μm

Using double heterojunction structure with linearly graded In_xAl_1–xAs as buffer layer and In_0.9Al_0.1As as cap layer, wavelength extended In_0.9Ga_0.1As detectors with cutoff wavelength of 2.88 μm at room temperature have been grown by using gas source molecular beam epitaxy, their characteristics have been investigated in detail and compared with the detectors cutoff at 2.4 μm with similar structure as well as commercial InAs detectors. Typical resistance area product R₀A of the detectors reaches 3.2 Ω cm² at 290 K. Measured peak detectivity reaches 6.6E9 cm Hz^1/2/W at room temperature.     

Bias-selectable mid-/long-wave dual band infrared focal plane array based on Type-II InAs/GaSb superlattice

In this paper, a mid-/long-wave dual-band detector which combined PπMN structure and unipolar barrier was developed based on type-II InAs/GaSb superlattice. A relevant 320 × 256 focal plane array (FPA) was fabricated. Unipolar barrier and PπMN structure in our dual band detector structure were used to suppress cross-talk and dark current, respectively. The two channels, with respective 50% cut-off wavelength at 4.5 μm and 10 μm were obtained. The peak quantum efficiency (QE) of mid wavelength infrared (MWIR) band and long wavelength infrared (LWIR) band are 53% at 3.2 μm under no bias voltage and 40% at 6.4 μm under bias voltage of −170 mV, respectively. And the dark current density under 0 and −170 mV of applied bias are 1.076 × 10⁻⁵ A/cm² and 2.16 × 10⁻⁴ A/cm². The specific detectivity of MWIR band and LWIR band are 2.15 × 10¹² cm·Hz^1/2/W at 3.2 μm and 2.31 × 10¹⁰ cm·Hz^1/2/W at 6.4 μm, respectively, at 77 K. The specific detectivity of LWIR band maintains above 10¹⁰ cm·Hz^1/2/W at the wavelength range from 4.3 μm to 10.2 μm under −170 mV. The cross-talk, selectivity parameter at 3.0 μm, about 0.14 was achieved under bias of −170 mV. Finally, the thermal images were taken by the fabricated FPA at 77 K.     

Analysis and applications of nanocavity structures used as tunable filters and sensors

This paper reports on a novel design for a tunable filter and plasmonic sensor based on the metal–insulator–metal waveguide with a nanocavity resonator. Simulation results show that as a one-channel filter, the resonance wavelengths show a linear red-shift with an increase in nanocavity length with a slope of 1742 nm/μm and a nonlinear blue-shift with an increase in nanocavity width, respectively. A two-channel filter can be realized using two nanocavities and the arrangement of the two nanocavities with respect to the waveguide and the value of the distance between the nanocavities has only a marginal effect on the filter notch wavelength. Finally, both in-slit and out-slit refractive index plasmonic sensors are investigated with a sensitivity of 710 nm/RIU and 250 nm/RIU, respectively.     

Improvement of R0A product of type-II InAs/GaSb superlattice MWIR/LWIR photodiodes

The effects of atomic hydrogen and polyimide passivation on R₀A product of type-II InAs/GaSb superlattice photo detectors for cut-off wavelength of both 6.5 μm and 12 μm were investigated. Low temperature current–voltage measurement shows that the use of atomic hydrogen during molecular beam epitaxy growth can improve R₀A product by 260% for 6.5 μm cut-off superlattice diodes and by 50% for 12 μm cut-off ones. The R₀A product of polyimide-passivated diodes with 12 μm cut-off is about 80% higher than those un-passivated ones. Wannier–Stark oscillations at higher reverse bias were observed for polyimide-passivated superlattice diodes with 12 μm cut-off. No Wannier–Stark oscillations were observed for un-passivated superlattice diodes, indicating that surface leakage current dominates in un-passivated diodes, while intrinsic dark current mechanisms such as tunneling and diffusion current dominate in polyimide-passivated diodes.