IR Photoresponse Research Articles

Performance analysis of a new Mid-Infrared phototransistor based on combined graded band gap GeSn sensitive-film and IGZO TFT platform

In this paper, a novel InGaZnO (IGZO) thin-film Mid-Infrared phototransistor (TF MIR PT) based on GeSn capping layer with band-gap grading (BGG) aspect is proposed and numerically investigated. Accurate numerical models are developed to study the device characteristics, where the sensor optical properties under MIR light exposure are investigated using FDTD method. Importantly, a new systematic approach based on introducing a new Figure of Merit (FoM) parameter combining noise effects, power consumption and IR photoresponse characteristics is proposed to efficiently investigate the device performance. It is found that the use of IGZO TFT platform combined with BGG GeSn sensitive layer paves the way for achieving enhanced IR photodetection characteristics, while maintaining low dark-noise effects and reduced power consumption. Moreover, it is revealed that the use of GeSn capping layer with BGG paradigm enables extended spectral sensitivity to MIR ranges, showing a high cutoff wavelength of 2.4 μm. Besides, the proposed GeSn/IGZO TF MIR PT demonstrates a giant responsivity of 550 A/W at a specific wavelength value of 1.7 μm, detectivity of 2.5 × 1014 Jones and over than 168 dB of signal-to-noise ratio. Therefore, these findings open the perspective for the design of alternative MIR sensors, offering improved photoresponse, low noise and reduced power consumption, which are highly suitable for newly emerging CMOS-compatible optical communication and optoelectronic applications.

Enhanced phase transition and infrared photoresponse characteristics in VO2(M1) thin films synthesized by DC reactive sputtering on different substrates

VO2(M1) films synthesized by sputtering on quartz and c-sapphire substrates exhibited good semiconductor-to-metal transition (SMT) and IR photoresponse properties.

Enhancement of infrared photo-responses of the Schottky gate region of an n-AlGaAs/GaAs heterojunction FET by a second light illumination

IR photo-responses of the Schottky-barrier gate region are investigated in an n-AlGaAs/GaAs FET. When the Schottky gate region is illuminated by an IR light with the energy above the Schottky barrier, IR photoelectrons are excited and transferred from the gate to the 2D electron gas channel, resulting in the generation of a photocurrent J DG. It is demonstrated that the photocurrent J DG is strongly enhanced, when a weak second light having photon energy above the GaAs band gap locally illuminates the ungated region of the FET; J DG is increased by about three times due to the second light of P 2nd = 0.3 μW, where the increase of J DG is nearly proportional to the second light power P 2nd. The second light effectively enhances the IR photo-response in the Schottky gate region, even though the intensity of the second light is much weaker than that of the IR light, and the irradiated position is far away (~1 mm) from the gate region. Comparing the experimental results with a theoretical model based on the electron drift and hole diffusion, the enhancement mechanism of the photocurrent J DG is clarified.

Highly responsive, low-bias operated SnSe2 nanostructured thin film for trap-assisted NIR photodetector

Abstract Photo detectors are very important for operation of various opto-electronic devices, like night vision camera, thermal imaging, remote sensing and so on. As the sizes of devices are shrinking day by day, it is important to make photo detectors which are small, robust, stable and have good responsitivity. Also the materials should be made from earth abundant elements and can be deposited using simple deposition techniques. Recently, good photo-detection capabilities in the infrared as well as visible range have been reported in metal dichalcogenides ( W S e 2 , M o S e 2 , S n S e 2 , S n S 2 , W S 2 , M o S 2 , P t S e 2 , P d S e 2 etc). S n S e 2 is made of earth abundant elements. In this study, we report IR photo response in S n S e 2 nanostructured thin films grown on soda lime glass (SLG) by thermal evaporation technique. IR (1064 nm) photo response behavior of the film is measured at different bias voltages in 100–400 mV range in steps of 100 mV and laser power density of 30–79 m W / c m 2 . The responsitivity of the device shows non-saturation of the traps states in the device. The value of responsitivity was 0.796 ± 0.003 mA/W (standard deviation) at 79 m W / c m 2 laser power density and 400 mV bias voltage and the rise/decay times were 276 ms/332 ms, respectively. It is to be noted that the photo response behavior of film was stable and reproducible even after keeping them in atmospheric conditions for many months. This shows the potential of S n S e 2 as a suitable material for various opto-electronic applications. To the best of our knowledge, the present study shows superior values of responstivity and response/recovery time of S n S e 2 thin film on SLG substrate.

Highly photoresponsive VO2(M1) thin films synthesized by DC reactive sputtering

We report synthesis, characterization and IR photoresponse properties of 150 ± 10 nm thick high quality VO2(M1) thin films synthesized by DC reactive sputtering. Phase formation was confirmed by X-ray diffraction and Raman spectroscopic measurements. Morphology and microstructure were analysed by atomic force microscope, scanning electron microscope and transmission electron microscope which revealed polycrystalline nature of nanosized films with root mean square (rms) roughness value of 8 ± 0.7 nm. Electrical measurements revealed 1st order transition of thin films with a change in resistance of more than two orders of magnitude and temperature coefficient of resistance, TCR of − 1.24% K−1 at 30 °C. The fabricated VO2(M1) IR photodetector exhibited excellent reproducible photoresponse properties when subjected to a 1064 nm laser under 250 mW cm−2 power density with a bias voltage of 5 V at the ambient conditions of temperature and pressure. The sensitivity, responsivity, external quantum efficiency and specific detectivity were observed to be 1775%, 40.09 mA W−1, 4.67% and 7.07 × 1011 Jones, respectively.

Low-cost VO2(M1) thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture for IR photodetection.

We report detailed structural, electrical transport and IR photoresponse properties of large area VO2(M1) thin films deposited by a simple cost-effective two-step technique. Phase purity was confirmed by XRD and Raman spectroscopy studies. The high quality of the films was further established by a phase change from low temperature monoclinic phase to high temperature tetragonal rutile phase at 68 °C from temperature dependent Raman studies. An optical band gap of 0.75 eV was estimated from UV-visible spectroscopy. FTIR studies showed 60% reflectance change at λ = 7.7 μm from low reflectivity at low temperature to high reflectivity at high temperature in a transition temperature of 68 °C. Electrical characterization showed a first order transition of the films with a resistance change of four orders of magnitude and TCR of −3.3% K−1 at 30 °C. Hall-effect measurements revealed the n-type nature of VO2 thin films with room temperature Hall mobility, μe of 0.097 cm2 V−1 s−1, conductivity, σ of 0.102 Ω−1 cm−1 and carrier concentration, ne = 5.36 × 1017 cm−3. In addition, we fabricated a high photoresponsive IR photodetector based on VO2(M1) thin films with excellent stability and reproducibility in ambient conditions using a low-cost method. The VO2(M1) photodetector exhibited high sensitivity, responsivity, quantum efficiency, detectivity and photoconductive gain of 5.18%, 1.54 mA W−1, 0.18%, 3.53 × 1010 jones and 9.99 × 103 respectively upon illumination with a 1064 nm laser at a power density of 200 mW cm−2 and 10 V bias voltage at room temperature.

Photodetection of Near and Middle IR Lasers by f-MWCNTs/Polythiophen Nanocomposite Detector

The combination of carbon nanotubes (CNT) and conducting polymers offers an attractive route for the production of novel compounds that can be used in a variety of applications such as sensors, actuators, and molecular scale electronic devices. In this work, functionalized multiwall carbon nanotubes (f-MWCNTs) were added in different load ratios (3 wt%, 5 wt% and 10 wt%) to thiophen (PTh) polymer to procedure PTh/CNTs nanocomposite and deposited on porous silicon substrate by electropolarization. Photoconductive detectors were fabricated using PTh/f-MWCNTs matrix to work in the near region and middle IR regions. These detectors were illuminated by semiconductor laser diode wavelength of 808(nm) and Nd-YAG laser of wavelength 1064 (nm) to study the I-V characteristics and figures of merit. FTIR spectra assignments verify that the thiophene groups were successfully introduced into the carbon nanotubes. SEM images reflect that the electro polymerization process gives well coating for the CNTs by PTh. The conductivity of PTh as a function of temperature increased about 30 times due to addition of f-MWCNTs. Figures of merit reflect a good IR radiation sensitivity and photo response. The specific detectivity was in order of 108 (cm.Hz1/2/W) for both IR regions. The rise and fall times of the output signal are about of 192 (μs) and 121 (μs) respectively for load ratio 5wt% of CNT, which consider good values for these types of detectors.

Improvement of QDIP performance due to quantum dots with built-in charge

The charging of quantum dots provides two strong effects which improve Quantum Dot Infrared Photodetector (QDIP) performance. First, electrons placed in the quantum dots enhance IR-induced transitions and increase electron coupling to IR radiation. Second, the built-in-dot charge creates potential barriers around dots and these barriers strongly suppress the photoelectron capture and exponentially increase the photoelectron lifetime. Both effects enhance the IR photoresponse. Long photoelectron lifetime decreases the generation–recombination noise and increases the device sensitivity. To investigate the potential profiles around charged dots, we used the nextnano3 software which allows for simulation of multilayer structures combined with realistic geometries in one, two, and three spatial dimensions. In weak electric fields the photoelectron kinetics and transport in the potential created by charged dots have been studied analytically. In strong fields the results were based on Monte-Carlo modeling. The effects of dot charging have been investigated in QD structures which were fabricated using molecular beam epitaxy. InAs quantum dots were grown on AlGaAs surfaces by deposition of approximately 2.1 monolayers of InAs. In the obtained structures the dot charging is realized via intra-dot and inter-dot doping. The increase in photoresponse due to dot charging is in good agreement with the model which takes into account anisotropy of potential barriers around QDs in QD layers.

Laser beam induced current measurements of Cd1−xZnxS/CdTe solar cells

The role of the window layer in Cd1−xZnxS/CdTe photovoltaic (PV) device structures was investigated using a triple wavelength laser beam induced current (LBIC) technique. Full pn structures were deposited using metal organic chemical vapour deposition (MOCVD). The triple wavelength LBIC technique allowed for the diagnostic analysis of carrier collection uniformity at 3 wavelength dependent photon penetration depths, δp. An assessment of the Cd1−xZnxS window layer film thickness and surface coverage showed a correlation between lateral device performance and window layer thickness distribution. Islands of thick Cd1−xZnxS were shown to increase localised blue absorption, correlating to isolated regions of increased red and IR photoresponse. Overall device open-circuit voltage, Voc is shown to demonstrate a linear dependence on thick (∼300nm) Cd1−xZnxS surface coverage. Voc and shunt resistance Rsh losses attributed to the window layer were found to jointly contribute to the overall cell efficiency losses. A non-uniform pin-hole distribution, leading to Rsh loss, was found to be independent of the overall Cd1−xZnxS thickness distribution; thus the triple wavelength LBIC measurement was able to identify causes for the observed losses in both Voc and Rsh.

Photoresponse in large area multiwalled carbon nanotube/polymer nanocomposite films

We present a near IR photoresponse study of large area multiwalled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (MWNT/P3HT-b-PS) nanocomposite films for different loading ratio of MWNT into the polymer matrix. We show that the photocurrent strongly depends on the position of the laser spot with maximum photocurrent occurring at the metal-film interface. In addition, compared to the pure MWNT film, the photoresponse is much larger in the MWNT/polymer composite films. The time constant for the photoresponse is slow and varies between 0.6 and 1.2 s. We explain the photoresponse by Schottky barrier modulation at the metal-film interface.

Electrical and optical properties of bismuth telluride/gallium nitride heterojunction diodes

Semiconducting bismuth telluride has a band gap energy of about 0.15eV at room temperature and is a good material for middle wavelength IR (MWIR) detection [S.K. Mishra, S. Satpathy, O. Jepsen, J. Phys. Condens. Matter, p. 461]. We have grown bismuth telluride thin films on gallium nitride (on sapphire) by pulsed laser deposition at a substrate temperature of 300°C. The structural characteristics and surface morphology of the films were studied by X-ray diffraction and scanning electron microscopy, respectively. The chemical composition of the as-deposited bismuth telluride thin films was determined by X-ray photoelectron spectroscopy and was found to be different from that of the bulk target, changing from stoichiometric Bi2Te3 to bismuth rich. A bismuth rich p-Bi2Te3/n-GaN/Al2O3 heterojunction was fabricated for photovoltaic detection of low energy photons. The wide band gap semiconducting n-GaN layer and the Al2O3 substrate act as a window for IR transmission. A sensitive IR photoresponse of the heterojunction is obtained by back-side illumination. The photocurrent measured is 0.18μA according to the irradiation change in the current–voltage characteristics. The current–voltage characteristics allow us to evaluate the series resistance (Rs), zero-bias resistance (R0) and ideality factors (n) of the junctions. Our results have suggested that bismuth telluride is a potential candidate for photovoltaic mid-infrared detection.

Infrared Photoresponse in Semi-Insulating GaAs Diode

In semi-insulating GaAs (SI GaAs) photodiodes, an IR photoresponse for longer wavelength beyond the energy gap threshold is observed. The sensitivity is analyzed by classifying electrode types and configurations. The IR sensitivity originates from the optical hole injection. When a cathode has an ohmic contact, the IR sensitivity is enhanced exponentially with the bias voltage. The enhancement of the IR sensitivity corresponds to the negative differential resistance in SI GaAs. The mechanism of the IR sensitivity is discussed in terms of the avalanche injection.