Barrier Photodetectors Research Articles

Enhanced Electron Photoemission by Collective Lattice Resonances in Plasmonic Nanoparticle-Array Photodetectors and Solar Cells

We propose to use collective lattice resonances in plasmonic nanoparticle arrays to enhance and tailor photoelectron emission in Schottky barrier photodetectors and solar cells. We show that the interaction between narrow-band lattice resonances (the Rayleigh anomaly) and broader-band individual-particle excitations (localized surface plasmon resonances) leads to stronger local field enhancement. In turn, this causes a significant increase of the photocurrent compared to the case when only individual-particle excitations are present. The results can be used to design new photodetectors with highly selective, tunable spectral response, which are able to detect photons with the energy below the semiconductor bandgap. The findings can also be used to develop solar cells with increased efficiency.

Demonstration of a large-area AlGaN/GaN Schottky barrier photodetector on Si with high detection limit

A high-quality AlGaN/GaN Schottky barrier photodetector was demonstrated on Si. The device exhibited a very low dark current of 0.94 fA at −2.5 V and 2.51 pA at −10 V. There were two spectral response peaks located at 280 and 340 nm, respectively, and the relative intensity of these peaks changed with applied bias. The responsivity exhibited optical power density dependence measured at 340 nm with different bias. The zero bias differential resistance of 3.63 × 1013 Ω and area product is calculated to be 4.10 × 1011 Ω cm2. The excellent current–voltage characteristics led to a detectivity performance of 4.98 × 1013 cm Hz1/2 W−1.

Metamorphic InAsSb-based barrier photodetectors for the long wave infrared region

InAs0.6Sb0.4/Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1−xInxSb buffer layers and GaSb substrates by molecular beam epitaxy. At the wavelength of 8 μm and T = 150 K, devices with 1-μm thick absorbers demonstrated an external quantum efficiency of 18% under a bias voltage of 0.45 V.

Low-Frequency Noise Characteristics of ZnO Nanorods Schottky Barrier Photodetectors

A Schottky barrier photodetector with ZnO nanorods is fabricated on a glass substrate and the I-V characteristics are investigated. The ZnO nanorods are synthesized by an aqueous method, which allowed the fabricated Schottky barrier photodetector to be more sensitive in the UV region. Under 370-nm illumination, the photocurrent of the ZnO nanorod Schottky barrier photodetector is 6.56 μA and the UV-to-visible ratio is 780.8 at -1V. In addition, the noise equivalent power and normalized detectivity (D*) of the photodetector are 6.74×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> W and 3.29 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at -1V, respectively.

Modeling of midwavelength infrared InAs/GaSb type II superlattice detectors

The performance of midwavelength infrared type II superllatice InAs/GaSb PIN and nBn (AlGaSb barrier) photodetectors in a reverse bias voltage range and a temperature range from 77 to 240 K is described. The PIN and nBn structures are modeled by a bulk based model, i.e., type II superllatice is treated as an artificial semiconductor material where parameters describing its physical properties are extracted from the experimental data. The model assumes that position of the effective trap energy level depends on temperature, what allowed to obtain a very good fitting to the measurements. Temperature and bias dependent dark current and differential resistance area product of the both devices have been analyzed to investigate contributing mechanisms such as: diffusion, generation-recombination, band-to-band and trap-assisted tunneling that limit the electrical performance of both types of the detectors. The I−V and RA(V) product characteristics of both types of type II superllatice InAs/GaSb photodetectors were found to be dominated by diffusion and generation-recombination currents in the nearly zero-bias region. At medium values of reverse bias, the trap-assisted tunneling reveals its significance, while at higher reverse voltages—the band-to-band tunneling is decisive to I−V and RA(V) characteristics. The fitting procedure allowed to extract both generation-recombination and diffusion components of carrier lifetimes pointing out that the carrier lifetimes range from 2 to 10 ns at T=200 K . Detectivity for T=240 K and V=50 mV was estimated to be 10 9 cmHz 1/2 /W and 4×10 9 cmHz 1/2 /W for PIN and nBn detector, respectively. Finally, type II superlattice InAs/GaSb PIN and nBn structures’ performance is compared to both unipolar barrier nBn HgCdTe detector and bulk HgCdTe photodiodes operated at near-room temperature. It is shown that the performance of SL and HgCdTe photo detectors with a cut-off of about 5 μm is comparable at operation temperatures around 240 K.

High quality AlN grown on double layer AlN buffers on SiC substrate for deep ultraviolet photodetectors

High quality AlN epilayers were grown on SiC substrates using double layer AlN buffers growth method by metal organic chemical vapor deposition and exploited as active deep ultraviolet optoelectronic materials through the demonstration of AlN Schottky barrier photodetectors. The grown AlN epilayers have smooth surfaces, low etch-pit density, narrow width of x-ray rocking curves, and strong band edge photoluminescence emission with low impurity emissions. AlN Schottky photodetectors are shown to possess outstanding features including extremely low dark current and high breakdown voltage.

Low-Frequency Noise Characteristics of GaN Schottky Barrier Photodetectors Prepared With Nickel Annealing

In this paper, GaN Schottky barrier photodetectors (PDs) prepared with and without Ni treatment were fabricated. I-V and noise characteristics of these devices were then investigated. Comparing the GaN PDs with and without Ni treatment, it was found that GaN PDs prepared with Ni treatment can not only reduce dark current, but also enhance the UV-to-Vis rejection ratio. With an applied bias of -2 V, it was found that noise equivalent power (NEP) and detectivity (D*) for the PDs prepared without Ni treatment were 9.95 × 10-8 W and 1.59 × 107 cmHz0.5W-1, respectively. At the same applied bias, it was also found that NEP and D* for PDs prepared with Ni treatment were 1.74 × 10-11 W and 9.07 × 1010 cmHz0.5W-1, respectively.

Characterization of carbon nanotube film-silicon Schottky barrier photodetectors

The authors fabricate vertical geometry single-walled carbon nanotube (CNT) film/p-type silicon Schottky barrier photodetectors, where the CNT film acts as the transparent metal and silicon as the active semiconductor. The authors experimentally characterize the current-voltage, spectral responsivity, and noise properties of these devices under reverse bias. The authors find that the CNT film–Si Schottky barrier photodetectors exhibit a large photocurrent-to-dark current ratio with responsivity as high as 0.10 A/W due to the high transmittance of the CNT film. The measured current noise spectral density shows a 1/f limited behavior and scales as the square of the reverse bias current. The noise equivalent power of the devices is found to be 1.4 × 10−10 W. A comparison between CNT film devices and devices based on conventional metal electrodes is also carried out. These results provide important insights into the properties and performance of CNT film–Si Schottky barrier photodetectors.

GaN-based MSM photovoltaic ultraviolet detector structure modeling and its simulation

Based on the principles of metal—semiconductor—metal Schottky barrier photodetectors (MSM-PD), using the carrier rate equations, the circuit simulation model of a GaN-based MSM photovoltaic ultraviolet detector is constructed through an appropriately equivalent process. By using the Pspice analytical function of Cadence soft on the model, the relationship between the photocurrent and the terminal voltage under different UV light powers is analyzed. The result shows that under the given UV power, the photocurrent increases and tends to become saturated gradually as the terminal voltage of the device increases, and that under different UV powers, the photocurrent increases with increasing incident power. Then the analysis of the relationship between the photocurrent and the terminal voltage under the different ratios of interdigital electrode space and width is carried out when the UV power is given. The results show that when the ratio of interdigital electrode space and width (L/W) equals 1, the photocurrent tends to be at a maximum.

Noise Characteristics of GaN Schottky Barrier Photodetectors with Patterned Sapphire Substrate

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GaN ultraviolet Schottky barrier photodetectors with ZrO2 or SiO2 insulators

GaN ultraviolet (UV) Schottky barrier photodetectors (PDs) with a ZrO2 or SiO2 layer were successfully fabricated. With an appropriate ZrO2 layer thickness, the dark current of Schottky barrier PDs could be notably suppressed, and the photogenerated carriers could still reach the electrodes by tunneling through the thin ZrO2 layer under illumination. A UV-to-visible rejection ratio of more than one order of magnitude can be found in the Schottky barrier PD with ZrO2 layers. It can be seen clearly that the cut-off occurred at approximately 360 nm while the responses above the band-gap were flat.

Performance of ZnO-Based Ultraviolet Photodetectors Under Varying Thermal Treatment

This paper reports fabrication, characterization, and testing of the thermal stability of ZnO-based Schottky ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si 〈100〉 substrate by the sol-gel technique. The surface morphological and the structural properties of the thin film were studied by an atomic force microscope (AFM) and a scanning electron microscope (SEM). For the investigation of the surface chemical bonding, X-ray photoelectron spectroscopy (XPS) measurements were also performed. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> characteristics of the Schottky barrier photodetector were studied, and the parameters such as ideality factor, leakage current, and barrier height were extracted from the measured data at room temperature. With applied bias voltages in the range from -3 to 3 V, the contrast ratio, responsivity, detectivity, and quantum efficiency of the photodetectors were measured for an incident optical power of 0.1 mW at 365-nm wavelength. The electrical and optical study revealed that the performance of the device improves with increasing post metal deposition annealing temperature up to 100°C. The device exhibited excellent thermal stability in the annealing temperature range of 100°C to 200°C. For annealing temperatures beyond 200°C, the performance of the device degrades drastically. It was also found that at under 200°C, there is a harmonious correlation between the photoresponse and electrical characteristics of the device. Above this temperature, there is no correlation between the variations of photoresponse and electrical characteristics with increasing annealing temperature. The variation of the electrical and photoresponse properties of the Schottky photodetector subjected to different post-fabrication annealing can be attributed to the combined effects of interfacial reaction and phase transition during the annealing process.

Thermally stable Ir/n-ZnO Schottky diodes

Temperature-dependent characteristics of ZnO Schottky diodes with Iridium (Ir) contact electrodes were investigated. Using Norde model, it was found that the effectively Schottky barrier heights of Ir on n-ZnO were around 0.837, 0.829, 0.801, 0.750 and 0.719 eV when measured at 25, 30, 50, 100 and 150 °C, respectively. Using Cheung’s method, it was found that Schottky barrier heights between Ir and the n-ZnO were 0.824, 0.823, 0.789, 0.743 and 0.740 eV when measured at 25, 30, 50, 100 and 150 °C, respectively. The large Schottky barrier heights suggest that Ir is a potentially useful material for ZnO-based ultraviolet Schottky barrier photodetectors and metal–semiconductor-metal photodetectors.

Mid-infrared quantum dot barrier photodetectors with extended cutoff wavelengths

A method to extend the cutoff wavelength of mid-infrared barrier photodetectors by incorporating self-assembled InSb quantum dots into the active area of the detector is demonstrated. This approach enables the extension of the cutoff wavelength of barrier photodetectors from 4.2 to 6 m, demonstrating infrared response at temperatures up to 225 K.

Raising a barrier

The range of mid-infrared barrier photodetectors has been extended to cover the whole 3-5 μm atmospheric transmission window by researchers at Jet Propulsion Laboratory (JPL) at California Institute of Technology in the US. By incorporating self-assembled quantum dots into the absorber of the photodetector, they increased the cutoff wavelength from 4.2 to 6 μm and demonstrated an infrared response at temperatures up to 225 K.

An instrument for measuring the intensity and dose of cancerigenic ultraviolet radiation

An instrument for measuring the intensity and dose of cancerigenic radiation from the Sun and artificial sources has been developed. A 4H-SiC Schottky barrier photodetector is used as the sensor. The sensitivity spectrum of the photoelectric transducer lies in the region 240–300 nm and has a maximum at 260 nm. The quantum efficiency is ≈0.3 electrons/photon (at λ = 254 nm), and its temperature coefficient at T = 250–310 K is < 0.1%/°C. The dimensions of the device are 3 × 6 × 11 cm.

Thin-Film Schottky Barrier Photodetector Models

Phenomenological models for the internal quantum efficiency of Schottky barrier photodetectors suitable for the detection of optical radiation below the bandgap energy of the semiconductor are presented and discussed. The detection mechanism is internal photoemission from the metal film into the semiconductor substrate. Three detector configurations are considered: the first consists of a thick metal film on a semiconductor substrate forming a single Schottky barrier; the second consists of a thin metal film on a semiconductor substrate also forming a single Schottky barrier; and the third consists of a thin metal film buried in semiconductor and forming two Schottky barriers (one along each metal-semiconductor interface). In the three cases, illumination through the semiconductor substrate is assumed. The two thin-film configurations provide enhanced internal quantum efficiencies due to multiple hot carrier reflections within the metal film, with the double-barrier case providing the greatest enhancement due to emission over two barriers. The models proposed are based on assessing the emission probability of hot carriers as a function of their energy, taking into account multiple reflections within the metal film and energy losses due to internal scattering (e.g., with phonons and cold carriers). The thin-film single-barrier model was tested via comparisons with responsivity measurements reported in the literature for PtSi/p-Si and Pd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si/p-Si detectors.

GaN Schottky Barrier Photodetectors Prepared on Patterned Sapphire Substrate

A high quality GaN Schottky barrier photodetector (PD) was prepared on patterned sapphire substrates (PSSs) by metallorganic chemical vapor deposition. Compared with the PD prepared on a conventional flat sapphire substrate, we can reduce dark current and enhance responsivity. Under a −2 V applied bias, noise equivalent power and normalized detectivity were and , respectively, for the PD prepared on PSS. These values were also better than those achieved from the PD prepared on a flat sapphire substrate.

Improved performance of GaN-based Schottky barrier photodetectors by annealing Ir/Pt Schottky contact in O 2

Nitride-based UV Schottky barrier photodetectors (PDs) with Ir/Pt after annealing in O 2 at 600 °C were fabricated successfully. With −5 V applied bias, the reverse leakage current of the annealed PD was 3.65 × 10 −12 A. It was found that we could achieve the larger Schottky barrier height, the smaller dark current and the larger photocurrent to dark current contrast ratio by annealing Ir/Pt. After annealing, the Schottky barrier height increased from 0.91 eV to 1.03 eV and the ideality factor decreased from 1.58 to 1.16. Such a result indicated that the dominant current transport mechanism may be thermionic emission and the Schottky contact is near-ideal after annealing. These results could be attributed to the formation of IrO x phase. It was also found that responsivity and the UV-to-visible rejection ratio were 0.19 A/W and 1.05 × 10 3 after annealing with −6 V applied bias.

GaN Schottky Barrier Photodetectors with a Semi-Insulating AlInN Cap Layer

UV GaN Schottky barrier photodetectors with a semi-insulating AlInN cap layer were proposed and fabricated. By inserting the AlInN cap layer, we can reduce the dark leakage current by more than 2 orders of magnitude compared with conventional devices. We can also use the AlInN cap layer to suppress the photoconductive gain, enhance the UV-to-visible rejection ratio, reduce the noise level, and enhance the detectivity.