S. S. Molchanov

MOCVD Growth and Mg-Doping of InAs Layers

Epitaxial layers of Mg-doped InAs were grown by MOCVD, and electrical properties of these layers were studied. The doping with magnesium in the course of MOCVD growth allows one to obtain strongly compensated p-InAs with a high hole density (p≈2×1018 cm−3) and a low carrier mobility (μ≈50 cm2/(V s)) at T=300 K. When the samples are lightly doped with Mg, neutral impurities are bound with Mg, and n-type InAs layers with a carrier mobility exceeding that in undoped samples are formed.

Broken-gap heterojunction in the p-GaSb-n-InAs1−x Sbx(0≤x≤0.18) system

Epitaxial InAs1−xSbx layers with the Sb content 0≤x≤0.18 were grown by metalorganic vapor phase epitaxy (MOVPE) on p-GaSb and n-InAs substrates. The photoluminescence (PL) spectra of the heterostructures were measured at T=77 K. The experimental PL data were used to study variation of the bandgap as a function of the InAsSb solid solution composition. The energy difference between the GaSb valence band top and the InAs0.82Sb0.18 conduction band bottom was calculated. It was established that GaSb/InAs1− xSbx with 0≤x≤0.18 represents a broken-gap heterojunction of type II.

Electroluminescent characteristics of InGaAsSb/GaAlAsSb heterostructure Mid-IR LEDs at high temperatures

The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hνmax = 0.693 − 4.497 × 10−4T). Based on the dependence Eg = hνmax − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, Eg ≅ 0.817 − 4.951 × 10−4T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage Ucut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (Ucut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout the temperature interval.

Portable optical water-and-oil analyzer based on a mid-IR (1.6–2.4 μm) optron consisting of an LED array and a wideband photodiode

An optical method for measuring the water and oil content using mid-IR (1.6–2.4 μm) LEDs and a wideband photodiode is suggested for the first time. This method is developed based on the absorption spectra of pure water, dewatered oil, and water—oil emulsions (cut oil) with different content of water and uses 10 types of LEDs in the spectral range 1.6–2.4 μm. It is shown that pure water heavily absorbs the LED radiation in the spectral range 1.85–2.05 μm, oil absorbs in the range 1.67–1.87 μm, and the LED radiation with a maximum at 2.20 μm is equally weakly absorbed by water and oil. An optical cell of the water-and-oil analyzer is designed on the basis of a three-element diode array with radiation maxima at 1.65 (detection of oil), 1.94 (detection of water), and 2.2 μm (reference signal) wideband photodiode covering the spectral range 1.3–2.4 μm. A calibration curve is derived that represents the dependence of the water concentration in oil on the amplitude of the reduced signal obtained by processing three signals from the LEDs. This optical method of measuring the water content in oil underlies a portable analyzer making possible online measurements directly in an oil well.

Powerful InAsSbP/InAsSb light emitting diodes grown by MOVPE

Mid-infrared light-emitting diodes (LEDs) operating in the 3.3-4.5 μm wavelength range at room temperature are produced on the basis of InAsSbP/InAsSb heterostructures. The photoluminescence of InAsSb layers and electroluminescence properties of LEDs are investigated. LEDs light-current characteristics are also studied. Fabricated were LEDs of A and B type, A being preferential for currents in excess of 200 mA, and B being better for the current range 0-200 mA. When operating at 5% duty cycle, at room temperature wavelength λ = 3.4 μm the pulse power of the diodes is measured as 1.2 mW under 1.3 A drive current.

InAs/InAsSbP light-emitting structures grown by gas-phase epitaxy

Using the metal-organic chemical vapor decomposition technique, light-emitting diodes based on InAs/InAsSbP double heterostructures emitting in a wavelength range around 3.3 µm have been fabricated. The external quantum yield of the diodes is 0.7%. In laser diodes, stimulated emission at a wavelength of 3.04 µm has been obtained at T=77 K.

Long-wavelength light-emitting diodes (λ=3.4–3.9 µm) based on InAsSb/InAs heterostructures grown by vapor-phase epitaxy

InAs/InAs0.93Sb0.07/InAs heterostructures were grown by metal-organic vapor-phase epitaxy in a horizontal reactor at atmospheric pressure. Based on the obtained structures, light-emitting diodes operating at λ=3.45 µm (T=77 K) and λ=3.95 µm (T=300 K) were fabricated. The room-temperature quantum efficiency of light-emitting diodes was 0.12%.

Electrical and electroluminescent properties of InAsSb-Based LEDs (λ = 3.85–3.95 μm) in the temperature interval 20–200°C

The temperature dependences of the electrical and electroluminescent properties of InAsSbP/InAsSb/InAsSbP heterostructure LEDs (λ ≈ 3.8−4.0 μm) are studied in the temperature interval 20–200°C. It is shown that the radiation power decreases with increasing temperature in a superexponential manner and that this decrease is associated primarily with a rise in the rate of Auger recombination. The position of the maximum in the radiation spectrum varies with temperature nonmonotonically, since radiative recombination is observed both in the active region and in the wide-gap layer. At room temperature, current through the heterostructure is tunneling current irrespective of the applied voltage polarity. As the temperature rises, either the thermal emission of charge carriers appears (direct bias) or the diffusion current becomes significant (reverse bias).

Characterization of light-emitting diodes based on InAsSbP/InAsSb structures grown by metal-organic vapor-phase epitaxy

Light-emitting diodes for the wavelength range λ=3.3–4.5 µm were fabricated on the basis of InAsSbP/InAsSb heterostructures grown by metal-organic vapor-phase epitaxy. The use of vapor-phase epitaxy made it possible to appreciably increase the phosphorus content in barrier layers (up to 50%) in comparison with that attainable in the case of liquid-phase epitaxy; correspondingly, it was possible to improve confinement of charge carriers in the active region of the structures. Photoluminescent properties of InAsSb layers, electroluminescent properties of light-emitting diodes, and dependences of the emission power on current were studied. Two types of light-emitting diodes were fabricated: (i) with extraction of emission through the substrate (type A) and (ii) with extraction of emission through the epitaxial layer (type B). The light-emitting diodes operating in the pulse mode (with a relative pulse duration of 20) had an emission power of 1.2 mW at room temperature.

Interfacial and interband lasing in an AnAs/InAsSbP heterostructure grown by vapor-phase epitaxy from metal-organic compounds

Sources of coherent radiation are fabricated on the basis of a double InAs/InAsSbP heterostructure, grown by vapor-phase epitaxy from metal-organic compounds, that includes a thick (3.3μm) active region. The spectral characteristics of diodes with various cavity lengths are studied, and light polarization is measured. It is established that the modes that compose the spectrum of radiation are controlled by radiative recombination at the heteroboundary and in the bulk of the active region. A new mode with a wavelength of intermediate value, lying between the wavelengths of the aforementioned kinds of radiation, is observed if the current exceeds the threshold value by 30%. This intermediate mode presumably results from an interaction between the modes related to the interfacial and interband radiative recombination, which are present in the cavity at the same time.