The Ir/Si/ErSi2 tunable infrared photoemission sensor

We present a new type of metal-silicon-metal infrared detector, the tunable infrared photoemission sensor (TIPS), whose photoresponse can be tuned by an externally applied bias. The physical detection process of this new device is based on the internal photoemission of optically excited carriers between the two metal layers of the vertical Ir/Si/ErSi₂/Si_sub system. We show that the experimental TIPS cut-off wavelength is shifted from around 2 urn to more than 6 urn with a quantum efficiency of 3% at 2 |i,m and more than 1% at 3 urn when a bias of less than IV is applied to the Ir electrode. The experimental quantum efficiency of such a heterostructure is quantitatively explained using a model derived from the Fowler photoemission formalism, taking into account the wavelength dependence of light absorbed in each metallic film and the four different photoemission processes present in the TIPS structure. Dark current measurements of the TIPS structure indicate that high detectivities (above 10¹⁰ cm√Hz /W at 2μm at 125K) may be expected with this new type of device.     

Low-Temperature Crystallized and Flexible 1D/3D Perovskite Heterostructure with Robust Flexibility and High EQE-Bandwidth Product

All-inorganic perovskite cesium lead triiodide (CsPbI₃) has attracted much attention among the perovskite family due to its excellent optoelectronic properties and chemical stability. However, the high-temperature crystallization process makes CsPbI₃ less compatible with commercially flexible substrates, limiting its application into flexible optoelectronics. Here, a cation of 1-(3-aminopropyl)-2pyrrolidinone (APP) is reported that can form 1D (APP)PbI₃ perovskite as templates, and significantly reduce the CsPbI₃ black-phase transition energy with a low annealing temperature of 75 °C, which further enables a flexible (APP)PbI₃/γ-CsPbI₃ (1D/3D) heterostructure photodetector on ITO/PET substrate. A high external quantum efficiency (EQE) greater than 2377% is observed along the orientated 1D/3D heterostructure. The high gain and low noise result in a high specific detectivity (D*) over 10¹² Jones under −0.6 V low bias. The optimized device structure brings a high EQE × bandwidth product of 119 kHz under a low driving bias. Due to the high toughness of orientated APP⁺ ions and the face-connected [PbI₃]⁻ chains structure as a strong energy absorber, the flexible photodetector also shows excellent phase stability and impressive flexibility, remaining >90% initial responsivity after over 20 000 times bending with potential flexible imaging application in harsh environments.     

Injection photodiode based on an n-CdS/p-CdTe heterostructure

The possibility of developing injection photodiodes with a tunable/reconfigurable? photosensitivity spectrum in the spectral range of 500–800 nm based on an n-CdS/p-CdTe heterostructure is shown. It is established that such a structure in the short-wavelength region λ = 500 nm has the highest spectral sensitivity S _λ ≈ 3 A/W in the forward direction at a bias voltage of V = +120 mV and S _λ ≈ 2 A/W in the reverse direction at a bias voltage of V = ?120 mV. The integrated sensitivity of the device is S _int = 2 400 A/lm under illumination with white light E = 3 × 10^?2 lx, at a bias voltage of V = +4.6 V, and temperature of T = 293 K. Upon illumination with the monochromatic light of an LG-75 laser with the wavelength λ = 625 nm, S _int = ?1400 A/W (illumination power P = 18 × 10^?6 W/cm², bias voltage V = +4.6 V, and temperature T = 293 K). High values of S _λ and S _int provide the highly efficient transformation of light energy into electrical energy at low illumination levels (P < 18 × 10^?6 W/cm²).     

Design and implementation of high-speed planar Si photodiodesfabricated on SOI substrates

We report high-speed interdigitated (nonmetalized) p-i-n Si photodiodes fabricated on SOI substrates that operate at low bias voltages and that offer easy integration with transistor fabrication processes. Devices fabricated with a finger spacing of 2 μm and a 3.75-μm-thick active layer achieved a 1.1-GHz bandwidth at a bias of -3 V with a peak efficiency of 29% (0.2 A/W) at 850 nm. Photodiodes with the same geometry that were fabricated on a 2.71-μm-thick active layer exhibited a 3.4-GHz bandwidth and a quantum efficiency of 24% (0.16 A/W) at 840 nm when biased at -3 V. The dark current of the photodiodes was less than 25 pA at -3 V, and the capacitance of the photodiodes was less than 265 fF at an applied bias of -3 V     

A Highly Sensitive Multi-element HgCdTe e-APD Detector for IPDA Lidar Applications

An HgCdTe electron avalanche photodiode (e-APD) detector has been developed for lidar receivers, one application of which is integrated path differential absorption lidar measurements of such atmospheric trace gases as CO₂ and CH₄. The HgCdTe APD has a wide, visible to mid-wave-infrared, spectral response, high dynamic range, substantially improved sensitivity, and an expected improvement in operational lifetime. A demonstration sensor-chip assembly consisting of a 4.3 μm cutoff HgCdTe 4 × 4 APD detector array with 80 μm pitch pixels and a custom complementary metal–oxide–semiconductor readout integrated circuit was developed. For one typical array the APD gain was 654 at 12 V with corresponding gain normalized dark currents ranging from 1.2 fA to 3.2 fA. The 4 × 4 detector system was characterized at 77 K with a 1.55 μm wavelength, 1 μs wide, laser pulse. The measured unit gain detector photon conversion efficiency was 91.1%. At 11 V bias the mean measured APD gain at 77 K was 307.8 with σ/mean uniformity of 1.23%. The average, noise-bandwidth normalized, system noise-equivalent power (NEP) was 1.04 fW/Hz^1/2 with a σ/mean of 3.8%. The measured, electronics-limited, bandwidth of 6.8 MHz was more than adequate for 1 μs pulse detection. The system had an NEP (3 MHz) of 0.4 fW/Hz^1/2 at 12 V APD bias and a linear dynamic range close to 1000. A gain-independent quantum-limited SNR of 80% of full theoretical was indicative of a gain-independent excess noise factor very close to 1.0 and the expected APD mode quantum efficiency.     

Low dark current inverted organic photodetectors employing MoOx:Al cathode interlayer

We report low dark current small molecule organic photodetectors (OPDs) with an inverted geometry for image sensor applications. Adopting a very thin MoO_x:Al cathode interlayer (CIL) in the inverted OPD with a reflective top electrode results in a remarkably low dark current density (J_d) of 5.6 nA/cm² at reverse bias of 3 V, while maintaining high external quantum efficiency (EQE) of 56.1% at visible wavelengths. The effectiveness of the CIL on the diode performance has been further identified by application to inverted OPDs with a semi-transparent top electrode, leading to a significantly low J_d of 0.25 nA/cm², moderately high EQE_{540 nm} of 25.8%, and subsequently high detectivity of 8.95 × 10¹² Jones at reverse bias of 3 V. Possible origins of reduced dark currents in the OPD by using the MoO_x:Al CIL are further described in terms of the change of interfacial energy barrier and surface morphology.     

Efficient organic near-infrared photodetectors based on lead phthalocyanine/C60 heterojunction

High efficiency organic small molecule near-infrared photodetectors (NIR-PDs) based on a lead phthalocyanine/C₆₀ planar heterojunction are demonstrated. The NIR-PDs show a broad-band response that extends to 1100 nm. The performance of the NIR-PDs is improved by using CuI as anode buffer layer. The optimized NIR-PD exhibits a response peak at about 900 nm with external quantum efficiencies (EQEs) of 19.7% at zero bias and 35.1% at −6 V, which are higher than other small molecule NIR-PDs reported. Comparable EQEs of 18.0% at zero bias and 33.2% at −6 V are found in the NIR-PD by further using 4,7-diphenyl-1,10-phenanthroline as cathode buffer layer. Meanwhile, the dark current is significantly reduced, which results in a high detectivity of 2.34 × 10¹¹ Jones at zero bias, which is among the highest detectivities reported for organic small-molecule NIR-PDs. Besides, the NIR-PDs show a reliable stability in ambient condition.     

Photoelectric and luminescence properties of GaSb-Based nanoheterostructures with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown by metalorganic vapor-phase epitaxy

The luminescence and photoelectric properties of heterostructures with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown on n-GaSb substrates by metalorganic vapor-phase epitaxy are investigated. Intense superlinear luminescence and increased optical power as a function of the pump current in the photon energy range of 0.6–0.8 eV are observed at temperatures of T = 77 and 300 K. The photoelectric, current-voltage, and capacitance characteristics of these heterostructures are studied in detail. The photosensitivity is examined with photodetectors operating in the photovoltaic mode in the spectral range of 0.9–2.0 μm. The sensitivity maximum at room temperature is observed at a wavelength of 1.55 μm. The quantum efficiency, detectivity, and response time of the photodetectors were estimated. The quantum efficiency and detectivity at the peak of the photosensitivity spectrum are as high as η = 0.6–0.7 and D _λmax ^* = (5–7) × 10¹⁰ cm Hz^1/2 W^?1, respectively. The photodiode response time determined as the rise time of the photoresponse pulse from 0.1 to the level 0.9 is 100–200 ps. The photodiode transmission bandwidth is 2–3 GHz. Photodetectors with a deep Al(As)Sb/InAsSb/Al(As)Sb quantum well grown on n-GaSb substrates are promising foruse in heterodyne detection systems and in information technologies.     

Highly efficient bluish green phosphorescent organic light-emitting diodes based on heteroleptic iridium(III) complexes with phenylpyridine main skeleton

A new series of heteroleptic iridium(III) complexes, bis(2-phenylpyridinato-N,C2′)iridium (2-(2′,4′-difluorophenyl)-4-methylpyridine), (ppy)₂Ir(dfpmpy) and bis(2-(2′,4′-difluorophenyl)-4-methylpyridinato-N,C2′)iridium (2-phenylpyridine) (dfpmpy)₂Ir(ppy), have been synthesized by using phenylpyridine as a main skeleton for bluish green phosphorescent organic light-emitting diodes (PhOLEDs). The Ir(III) complexes showed high thermal stability and high photoluminescent (PL) quantum yields of 95% ± 4% simultaneously. As a result, the PhOLEDs with the heteroleptic Ir(III) complexes showed excellent performances approaching 100% internal quantum efficiency with a very high external quantum efficiency (EQE) of ∼27%, a low turn-on voltage of 2.4 V, high power efficiency of ∼85 lm/W, and very low efficiency roll-off up to 20,000 cd/m².     

Low dark current and internal gain mechanism of GaN MSM photodetectors fabricated on bulk GaN substrate

Metal-semiconductor-metal ultraviolet photodetectors are fabricated on low-defect-density homoepitaxial GaN layer on bulk GaN substrate. The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is ∼5 × 10⁶ cm⁻². The photodetector with a high UV-to-visible rejection ratio of up to 1 × 10⁵ exhibits a low dark current of <2 pA at room temperature under 10 V bias. The photo-responsivity of the photodetector gradually increases as a function of applied bias, resulting in a photodetector quantum efficiency exceeding 100% at above medium bias. The photo-responsivity also shows a dependence on the incident optical power density and illumination conditions. The internal gain mechanism of the photodetector is attributed to photo-generated holes trapped at the semiconductor/metal interface as well as high-field-induced image-force lowering effect.     

Optocoupler made from semiconducting polymers

Optocouplers (optoisolators) were fabricated using semiconducting polymers. The input unit is a polymer light emitting diode with an external quantum efficiency of ∼1% photons/electron. The output unit is a polymer photodiode with a quantum yield of ∼35% electrons/photon at 590 nm. Both units can be operated at bias voltages sufficiently low to be compatible with TTL and complementary metal-oxide semiconductor logic circuits. Since the transfer characteristic is nearly linear, the polymer optocoupler can be used in analogue circuits as well. The current transfer ratio reaches 2 × 10⁻³ under-10V reverse bias, comparable to that of commercial inorganic optocouplers.     

Injection photodiode based on a p-Si-n-CdS-n +-CdS structure

An injection photodiode with a high room-temperature rectification factor (10⁵) is developed based on a p-Si-n-CdS-n ⁺-CdS structure. It is shown that the light and dark current-voltage characteristics of the structure have identical features. It is found that the mode of “long” diodes is implemented in the structure at current densities of I = 10^?2?5 × 10^?4 A/cm²; in this case, the integral (S _int) and spectral (S _λ) sensitivities sharply increase. It is shown that S _int = 2.8 × 10⁴ A/lm (3 × 10⁶ A/W) for an illuminance of E = 0.1 lux and S _λ = 2.3 × 10⁴ A/W under laser irradiation with λ = 625 nm and a power of P = 10 μW/cm² at a bias voltage of V = 20 V. It is shown that the mechanism of photocurrent amplification is predominantly associated with ambipolar carrier-mobility modulation.     

A hybrid white organic light-emitting diode with stable color and reduced efficiency roll-off by using a bipolar charge carrier switch

A hybrid white organic light-emitting diode (WOLED) with an emission layer (EML) structure composed of red phosphorescent EML/green phosphorescent EML/spacer/blue fluorescent EML was demonstrated. This hybrid WOLED shows high efficiency, stable spectral emission and low efficiency roll-off at high luminance. We have attributed the significant improvement to the wide distribution of excitons and the effective control of charge carriers in EMLs by using mixed 4,4′,4″-tri(9-carbazoyl) triphenylamine (TCTA) and bis[2-(2-hydroxyphenyl)-pyridine] beryllium (Bepp₂) as the host of phosphorescent EMLs as well as the spacer. The bipolar mixed TCTA:Bepp_2, which was proved to be a charge carrier switch by regulating the distribution of charge carriers and then the exciton recombination zone, plays an important role in improving the efficiency, stabilizing the spectrum and reducing the efficiency roll-off at high luminous. The hybrid WOLED exhibits a current efficiency of 30.2 cd/A, a power efficiency of 32.0 lm/W and an external quantum efficiency of 13.4% at a luminance of 100 cd/m², and keeps a current efficiency of 30.8 cd/A, a power efficiency of 27.1 lm/W and an external quantum efficiency of 13.7% at a 1000 cd/m². The Commission Internationale de l’Eclairage (CIE) coordinates of (0.43, 0.43) and the color rendering index (CRI) of 89 remain nearly unchanged in the whole range of luminance.     

Photovoltaic detector based on type II heterostructure with deep AlSb/InAsSb/AlSb quantum well in the active region for the midinfrared spectral range

Photodetectors for the spectral range 2–4 μm, based on an asymmetric type-II heterostructure p-InAs/AlSb/InAsSb/AlSb/(p, n)GaSb with a single deep quantum well (QW) or three deep QWs at the heterointerface, have been grown by metal-organic vapor phase epitaxy and analyzed. The transport, luminescent, photoelectric, current-voltage, and capacitance-voltage characteristics of these structures have been examined. A high-intensity positive and negative luminescence was observed in the spectral range 3–4 μm at high temperatures (300–400 K). The photosensitivity spectra were in the range 1.2–3.6 μm (T = 77 K). Large values of the quantum yield (η = 0.6−0.7), responsivity (S _λ = 0.9−1.4 A W^–1), and detectivity (D* _λ = 3.5 × 10¹¹ to 10¹⁰ cm Hz^1/2 W⁻¹) were obtained at T = 77–200 K. The small capacitance of the structures (C = 7.5 pF at V = −1 V and T = 300 K) enabled an estimate of the response time of the photodetector at τ = 75 ps, which corresponds to a bandwidth of about 6 GHz. Photodetectors of this kind are promising for heterodyne detection of the emission of quantum-cascade lasers and IR spectroscopy.     

Large-signal analysis of the silicon pnp-BARITT diode

A numerical large-signal analysis of the silicon pnp BARITT diode is presented. This extends previous works to practical device structures. The diode admittance, power generation density, efficiency and quality factor are studied as functions of oscillation amplitude, frequency and bias current density. The results are found to be in substantial agreement with large-signal experimental measurements. A typical pnp structure optimised for operation at 10 GHz has an active region doping density of 2 × 10¹⁵/cm³, a width of 5.5 μm and a punch-through voltage of 40 V. Negative resistance occurs over the frequency range from about 8 GHz to about 14 GHz. The device Q at 10 GHz varies from a small-signal value of about ?10 to a large-signal value of about ?100. The conversion efficiency at 10 GHz is about 5% at a bias current density of 25 A/cm² and falls to about 2% at 200 A/cm². Maximum r.f. power output occurs at an r.f. amplitude of about 15 V and rises with bias current density to a maximum value of about 170 W/cm² at 200 A/cm².     

1/f noise in large-area Hg<Subscript>1−x</Subscript>Cd<Subscript>x</Subscript>Te photodiodes

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg_1−xCd_xTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10⁻¹⁵A/Hz^1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth i_n(f = 1 Hz, V_d = −60 mV, and Δf = 1 Hz) to dark current I_d(V_d = −60 mV) was α_SW-d = i_n/I_d ∼ 1 × 10⁻³. The SWIR detectors measured at 0 mV under illuminated conditions had median α_SW-P = i_n/I_ph ∼ 7 × 10⁻⁶. For mid-wave infrared (MWIR) detectors, α_MW-d = i_n/I_d ∼ 2 × 10⁻⁴, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in α_MW-P = i_n/I_ph = 4.16 ± 1.69 × 10⁻⁶. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, α_MW-P, in the mid 10⁻⁶ range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, α_LW-d = i_n/I_d ∼ 6 × 10⁻⁶, for the best performers. The majority of the LWIR detectors exhibited α_LW-d on the order of 2 × 10⁻⁵. The photo-induced 1/f noise had α_LW-P = i_n/I_ph ∼ 5 × 10⁻⁶. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.     

Investigation of broad-band quantum-well infrared photodetectorsfor 8-14-μm detection

Typical quantum-well infrared photodetectors (QWIPs) exhibit a rather narrow spectral bandwidth of 1-2 μm. For certain applications, such as spectroscopy, sensing a broader range of infrared radiation is highly desirable. In this paper, we report the design of four broad-band QWIPs (BB-QWIPs) sensitive over the 8-14-μm spectral range. Two n-type BB-QWIPs, consisting of three and four quantum wells of different thickness and/or composition in a unit cell which is then repeated 20 times to create the BB-QWIP structure, are demonstrated. The three-well n-type In_xGa_1-xAs-Al_yGa_1-yAs BB-QWIP was designed to have a response peak at 10 μm, with a full-width at half-maximum (FWHM) bandwidth that varies with the applied bias. A maximum bandwidth of Δλ/λ_p=21% was obtained for this device at V_b=-2 V. The four-well n-type In_xGa_1-xAs-GaAs BB-QWIP not only exhibits a large responsivity of 2.31 A/W at 10.3 μm and V_b=+4.5 V, but also achieves a bandwidth of Δλ/λ_p=29% that is broader than the three-well device. In addition, two p-type In _xGa_1-xAs-GaAs BB-QWIPs with variable well thickness and composition, sensitive in the 7-14-μm spectral range, are also demonstrated. The variable composition p-type BB-QWIP has a large FWHM bandwidth of Δλ/λ_p=48% at T=40 K and V_b=-1.5 V. The variable thickness p-type BB-QWIP was found to have an even broader FWHM bandwidth of Δλ/λ _p=63% at T=40 K and V_b=1.1 V, with a corresponding peak responsivity of 25 mA/W at 10.2 μm. The results show that a broader and flatter spectral bandwidth was obtained in both p-type BB-QWIP's than in the n-type BS-QWIP's under similar operating conditions     

High sensitivity organic photodiodes with low dark currents and increased lifetimes

Organic semiconductors hold the promise for large-area, low-cost image sensors and monolithically integrated photonic microsystems. This requires the availability of photodiodes offering at the same time high quantum efficiency, low noise and long lifetimes. Although published structures of organic photodiodes offer high external quantum efficiencies (EQE) of up to 76% [F. Padinger, R.S. Rittberber, N.S. Sariciftci, Effects of postproduction treatment on plastic solar cells, Advanced Functional Materials 13 (2003) 1, P. Schilinsky, C. Waldauf, C.J. Brabec, Recombination loss analysis in polythiophene based bulk heterojunction photodetectors, Applied Physics Letters 81 (20) (2002) 3885], [1], [2] they normally suffer from short lifetimes of only a few hundred hours as well as large dark currents. In our work the lifetime of a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) heterojunction photodiode structure was increased to several thousand hours by omitting the widely used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) anode layer. In addition, a simple model of optical interference and absorption effects was used to find the optimum thickness that combines high quantum efficiency with low dark current. As a result, we report on organic photodiodes with state-of-the-art EQE of 70% at 0 V bias, an on/off current ratio of 10⁶ at −1 V and 40 mW/cm² illumination, dark current densities below 10 nA/cm² at −1 V, and a lifetime of at least 3000 h.     

Very high-speed ultraviolet photodetectors fabricated on GaN

We report on the temporal and the frequency response of both metal-semiconductor-metal (MSM) and p-i-n ultraviolet photodetectors fabricated on single-crystal GaN. The best MSM devices show a fast 10–90% rise-time of ∼28 psec under comparatively low ultraviolet excitation of ∼0.1 W/cm² averagerirradiance. The fast-Fourier transform (FFT) of the pulse response data indicates a bandwidth, f_3dB, of ∼3.8 GHz at a reverse bias of 25 V. This agrees well with the direct frequency response measurement value of ∼3.5 GHz. For the p-i-n devices, we measured a rise-time of ∼43 psec at 15 V reverse bias for a 60 μm diameter mesa with 1 μm thick intrinsic region. The FFT of the p-i-n pulse response obtains f_3dB ≈1.4 GHz. Analysis in terms of reverse bias and geometric scaling indicates that the MSM photodetectors are transit-time limited. The p-i-n devices also show evidence of transit-time limited effects based on trends with respect to reverse bias and intrinsic region thickness. However, our larger area p-i-n devices show clear evidence of RC-limited behavior. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity. We have also found preliminary evidence of microplasmic effects in the p-i-n devices.     

High-speed photodiodes for the mid-infrared spectral region 1.2–2.4 μm based on GaSb/GaInAsSb/GaAlAsSb heterostructures with a transmission band of 2–5 GHz

High-speed p-i-n photodiodes for the spectral range of 1.2–2.4 μm are fabricated for the first time based on a GaAs/GaInAsSb/GaAlAsSb heterostructure with separated sensitive-(50 μm in diameter) and contact mesas, which are connected by a bridge front contact. The use of an unconventional design for the contact mesa with a Si₃N₄ insulating sublayer 0.3 μm thick under the metal contact made it possible to lower both the intrinsic photodiode capacitance and the reverse dark currents. The photodiodes have a low intrinsic capacitance of 3–5 pF at zero bias and 0.8–1.5 pF at a reverse bias of 3.0 V. The photodiode operating speed, which is determined by the time of increasing the photoresponse pulse to a level of 0.1–0.9, is 50–100 ps. The transmission band of the photodiodes reaches 2–5 GHz. The photodiodes are characterized by low reverse dark currents I _d = 200–1500 nA with a reverse bias of U = ?(0.5–3.0) V, a high current monochromatic sensitivity of R _i = 1.10–1.15 A/W, and a detectability of D*(λ_max, 1000, 1) = 0.9 × 10¹¹ W^?1 cm Hz^1/2 at wavelengths of 2.0–2.2 μm.