G. G. Konovalov

Photodiodes based on InAs/InAs0.88Sb0.12/InAsSbP heterostructures for 2.5–4.9 μm spectral range

Photodiodes with a photosensitive area diameter of 0.3 mm operating at room temperature in a middle-IR (2.5–4.9 μm) wavelength range have been created based on InAs/InAs0.94Sb0.06/InAsSbP/InAs0.88Sb0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. Distinguishing features of the proposed photodiodes are a high monochromatic responsivity, which reaches a maximum of 0.6–0.8 A/W at λmax = 4.0–4.6 μm, and a low dark current density of (1.3–7.5) × 10−2 A/cm2 at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 700–800 Ω. The detection ability of photodiodes in the spectral interval of maximum sensitivity reaches (5–8) × 108 cm Hz1/2 W−1.

Photodiodes based on InAs/InAsSb/InAsSbP heterostructures with quantum efficiency increased by changing directions of reflected light fluxes

It is shown, using the example of InAs/InAsSb/InAsSbP heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of a photodiode chip leads to an increase in the quantum efficiency of photodiodes by a factor of 1.5–1.7 in the entire mid-IR wave-length interval studied (λ = 3–5 μm). For the obtained photodiodes with a cutoff wavelength of 4.8 μm, a photosensitive area of 0.1 mm2, and a chip area of 0.9 mm2, a monochromatic responsivity at λ = 4.0 μm reached 0.6 A/W, while a dark current at a reverse bias voltage of 0.2 V was within 4–6 A/cm2.

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 (Sλ = 0.9−1.4 A W–1), and detectivity (D*λ = 3.5 × 1011 to 1010 cm Hz1/2 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.

Enhancement of the spectral sensitivity of photodiodes for the mid-IR spectral range

A new method is used to raise the spectral sensitivity of photodiodes based on GaSb/GaInAsSb/GaAlAsSb heterostructures for the spectral range 1.1–2.4 μm. It is shown that, with a profile formed as pits on the metal-free unilluminated rear surface area of the photodiode chip, it is possible to improve the spectral sensitivity of the photodiodes at wavelengths in the range 1.8–2.4 μm. The most pronounced increase of up to 53% at the sensitivity maximum, compared with the sensitivity of conventional photodiodes with a fully metallized rear surface of the chip, is observed for photodiodes with shallow pits 30 μm in radius on their rear surface. These devices can find wide application in systems measuring the amount of water in petroleum products and the moisture content of paper, soil and grain.

Improvement in the quantum sensitivity of InAs/InAsSb/InAsSbP heterostructure photodiodes

InAs/InAs0.88Sb0.12/InAs0.50Sb0.20P0.30 heterostructure photodiodes operating at room temperature in the spectral range 1–4.8 μm are developed. It is shown that the formation of a curvilinear reflecting surface constituted by a number of hemispheres on the rearside of the photodiode chip leads to an increase in the quantum sensitivity of the photodiodes by a factor of 1.5–1.7 at wavelengths in the range 2.2–4.8 μm. At an exposed photodiode area of 0.9 mm2 and a p-n junction area of 0.15 mm2, a zero-bias differential resistance of 30 Ω and a quantum sensitivity of 0.24 electron/photon at a wavelength of 3 μm are obtained. The operation of a photodiode with re-reflection of the photon flux in the crystal due to reflection from the curvilinear surface of the rearside of the photodiode chip is theoretically analyzed. The possibility of effective conversion of the re-reflected flux of photons into a photocurrent, with a simultaneous decrease in the p-n junction area, is demonstrated. An increase in the quantum sensitivity in the short-wavelength spectral range 1–2.2 μm by 35% relative to the calculated data is observed, which is probably due to impact ionization in the narrow-gap active region.

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 Id = 200–1500 nA with a reverse bias of U = −(0.5–3.0) V, a high current monochromatic sensitivity of Ri = 1.10–1.15 A/W, and a detectability of D*(λmax, 1000, 1) = 0.9 × 1011 W−1 cm Hz1/2 at wavelengths of 2.0–2.2 μm.

Photovoltaic Detector Based on Type II Heterostructure with Deep AlSb/InAsSb/AlSb Quantum Well in the Active Region for the Mid-Infrared 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 analysed. 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 quantum efficiency (η = 0.6–0.7), responsivity (Sλ = 0.9–1.4 A·W1), and detectivity D*λ 3.5·1011 to 1010 cm·Hz1/2·W−1) were obtained at T = 77–200 K. The small capacitance of the structures (C = 1.5 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.

Room-temperature photodiodes based on InAs/InAs0.88Sb0.12/InAsSbP heterostructures for extended (1.5–4.8 μm) spectral range

Photodiodes with a photosensitive area of 0.45 × 0.45 mm2 operating at room temperature in a wavelength range bounded by 4.9 μm have been created on the basis of InAs/InAs0.94Sb0.06/InAsSbP/InAs0.88Sb0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. A distinguishing feature of the proposed photodiodes is extended (λmax = 1.5–4.8 μm) spectral sensitivity range, in which the photodiode is characterized by a monochromatic responsivity of 0.5–0.8 A/W and a dark current density of 1.0–1.5 A/cm2 at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 20–100 Ω. The detection ability of photodiodes in the region of maximum sensitivity reaches (1–2) × 108 cm Hz1/2 W−1.

Fast-response p-i-n photodiodes for 0.9–2.4 μm wavelength range

Fast-response, uncooled p-i-n photodiodes with a long-wavelength spectral sensitivity boundary at λ = 2.4 μm have been created on the basis of GaSb/GaInAsSb/GaAlAsSb heterostructures. A low doping level (1014–1015 cm−3) in the active layer ensured a low capacitance of the photodiode structure (below 1 pF at a sensitive area diameter of 100 μm) and a record small response time (on a level of 100–150 ps). The photodiode pass band reaches up to 2 GHz. The proposed devices are characterized by a small dark current level (500–1000 nA at a reverse bias voltage of 1–3 V) and a detection ability reaching 9 × 1010 cm Hz1/2 W−1 in a spectral interval of maximum sensitivity within 1.9–2.2 μm.

Photoelectric properties of photodiodes based on InAs/InAsSbP heterostructures with photosensitive-area diameters of 0.1–2.0 mm

The results of a study aimed at the development of high-efficiency photodiodes for the spectral range 1.5–3.8 μm with various photosensitive-area diameters in the range 0.1–2.0 mm are reported. Epitaxial techniques for the growth of InAs/InAsSbP photodiode heterostructures are developed. The distinctive features of the diodes are their high monochromatic current sensitivity Sλ of up to 1.6 A/W at the peak of the spectrum, λ = 3.0–3.4 μm, and the detectivity of the photodiodes, estimated by the experimentally measured noise level and the monochromatic current sensitivity, reaching at the spectrum peak a value of D* (λmax, 1000, 1) = (0.6–12) × 1010 cm Hz1/2 W–1 at T = 300 K. The bulk component of the reverse dark current in the photodiodes under study is constituted by two components: diffusion- and tunneling-related, with a low density of reverse dark currents j = (0.3–6) × 10–1 A/cm2 attained at a bias of U =–(0.2–0.4) V. The photodiodes are characterized by the product R0A = 0.4–3.2 Ω cm2. With the diameter of the photosensitive-area increased within the range 0.1–2.0 mm, the specific detectivity of a photodiode increases by nearly a factor of 2, which is due to the weaker effect of surface leakage currents with its increasing diameter. The response time of diodes of this kind varies within the range 1–300 ns, which enables their use in open-space optical communication systems in the atmospheric-transparency window. Photodiodes with a large sensitive area (up to 2.0 mm), high specific detectivity, and high photosensitivity can be used to detect absorption bands and record the concentrations of such substances as methane, ether, N2O, and phthorothanum.