M. V. Stepanov

3.3-μm LEDs for measuring methane

LEDs have been created that emit in the region of the fundamental absorption band of methane at a wavelength of 3.3 μm for fast-response gas analyzers. A continuous optical power of 0.13 mW (cw) is achieved, and the peak optical power is 2.2 mW (the pulsewidth is 50 0μs, and the inverse duty cycle is 1.6×102). The current dependence of the optical power on the pump-pulse parameters is studied, and the conditions are found under which the peak power of the radiation of the LEDs in the mid-IR region is maximized.

Electrical properties of epitaxial indium arsenide and narrow band solid solutions based on it

The electrical properties of epitaxial InAs and solid solutions based on it (InGaAsSb, InAsSbP, InAsGa, InAsP) have been investigated. It is shown that intentionally undoped crystals have n-type conductivity, which is determined by shallow donor impurities (E1=0.002–0.003 eV) and structural defects (E2=0.02–0.03 eV and E3=0.09–0.10 eV). It is shown that growth of epitaxial InAs using the neutral solvent Pb and also rare-earth elements makes it possible to reduce the electron density by almost an order of magnitude (to levels as low as 3×1015 cm−3) due to due to a decrease in the density of structural defects.

Short-wavelength current tuning of InAsSb/InAsSbP heterostructure lasers caused by an injection nonuniformity

A reduction in the emission wavelength in the preferred mode of InAsSbP/InAsSb/InAsSbP heterostructure lasers by 50Å is observed when the current is raised from 1.8 to 5 times the threshold with dc and pulsed power. A comparison of the spectral and spatial distributions of the output as functions of current shows that this short-wavelength tuning is caused by a change in the distribution of the nonequilibrium charge carrier concentration over the strip width as the current is varied. This effect is modeled mathematically, taking into account the increase in the injection density and the drop in the output intensity from the middle to the sides of the waveguide. The results of the model calculation are in good agreement with experiment.

InAsSb light-emitting diodes for the detection of CO2 (λ=4.3 μm)

The main characteristics of room-temperature light-emitting diodes (λ=4.3 μm) based on InAsSbP/InAsSb/InAsSbP III–V semiconductor heterostructures with a variable-gap buffer layer are reported. An optical power P=0.85 mW was achieved with a pulse length of ∼5 μs and 1 kHz repetition frequency. Conditions for maximizing the power of the light-emitting diodes are indicated. An example is given of the use of these diodes to detect carbon dioxide using the 4.3 μm fundamental absorption band.

Rapid tuning of the generation frequency of InAsSb/InAsSbP diode lasers (λ=3.3 µm) due to nonlinear optical effects

A study has been made of wavelength tuning in double heterostructure InAsSb/InAsSbP-based diode lasers. A simple mathematical model, which takes into account the spatially homogeneous injection and the dependence of the dielectric constant on the charge carrier density, is discussed. The wavelength can be increased or decreased, depending on the pump current and diode structure parameters, as is observed experimentally. The process of wavelength tuning proceeds with virtually zero delay time since it is determined by the photon lifetime in the cavity and in part by the lifetime of nonequilibrium charge carriers.

InAsSb/InAsSbP diode lasers with separate electrical and optical confinement, emitting at 3–4 µm

Diode lasers based on InAsSb/InAsSbP with separate electrical and optical confinement, emitting in the wavelength interval 3–4 µm, are investigated. The lasers attain a higher operating temperature when electrical confinement is created by means of type-II heterojunctions. Interface Auger recombination is suppressed in lasers of this type, and the experimental current density is close to the theoretically calculated value for the case of predominant volume Auger recombination at a temperature of 180–220 K.

InAsSb/InAsSbP heterostructure lasers with a large range of current tuning of the lasing frequency

The lasing spectra and the shift in the position of the modes in the current range (1–5)Ith with various methods of pumping the nonequilibrium charge carriers are analyzed. It is shown that the pumping method does not influence the character of the tuning of the radiation line. The large short-wavelength tuning range (up to 50 Å) is due not to the heating of the crystal lattice in the active-region material but rather the nonuniform nonequilibrium charge-carrier density distribution over the width of the stripe.

Fast tuning of 3.3 μm InAsSb/InAsSbP diode lasers due to nonlinear optical effects

Abstract InAsSb/InAsSbP double heterostructure diode lasers for the spectral range of 3.3 μm grown by liquid phase epitaxy have been investigated. Emission spectra, far-field patterns and wavelength tuning versus current have been studied in the wide current range from threshold value I th up to 3 I th , at the temperature of liquid nitrogen. Controlled by current wavelength tuning in single-mode lasing has been obtained both towards the shorter wavelengths (up to 4.56 cm −1 ) and towards the longer wavelengths (up to 0.9 cm −1 ) at the temperature T =77 K. Comparison of the emission properties of the lasers, driven by different types of current (short pulse current, sawtooth pulse current and in quasi cw regime) showed the same quantum-mechanical nature of current tuning. The theoretical model of this nonlinear optical phenomenon is proposed. The estimated times of current tuning defined mainly by the photon lifetime in the cavity are about 10 −9 –10 −12 s.

Influence of pumping uniformity on current tuning of the emission wavelength of InAsSb/InAsSbP diode lasers

An investigation was made of continuous tuning of the emission wavelength in two types of InAsSb/InAsSbP diode heterolasers: three-layer structures with combined electrical and optical confinement and five-layer structures with separate confinement. In three-layer structures the emission wavelength initially decreases by 2–4 Å with increasing current and then increases by 10–15 Å. In five-layer structures the emission wavelength mainly decreases. This difference is attributed to the better flow of carriers in the bulk of the active region in five-layer structures as compared with three-layer ones.

Spatial beam oscillations in stripe lasers utilizing InAsSb/InAsSbP heterojunctions

Anomalously narrow, single-lobe and double-lobe beam directivity patterns in the plane of the p-n junction have been observed in lasers constructed from InAsSb/InAsSbP heterojunctions emitting at a wavelength of approximately 3.3 µm. Theoretical near-field and far-field radiation distributions for the laser emission of two beams oscillating across the stripe are obtained on the basis of new concepts of the lasing processes. The single-lobe directivity pattern is obtained for the emission of in-phase beams, and the double lobe is obtained for antiphase beams. Correspondence of the theory with experiment is established.