N. M. Kolchanova

The spectral linewidth of tunable semiconductor InAsSb/InAsSbP lasers emitting at 3.2–3.6 μm (2800–3100 cm−1)

A method was used to measure the width of emission lines of a type of semiconductor laser with composition InAsSb/InAsSbP. This type of laser was manufactured specially for absorption high-resolution spectroscopy of gases absorbing in the 2800–3100 cm−1 region. Parameters used for calculation of spectral emission linewidths were obtained using selected rotation-vibration lines of the gaseous molecules N2O, CH3Cl, and OCS. The estimated spectral emission linewidths varied in the range 10–30 MHz in dependence of the current passing and the type of laser.

Current-tunable lasers with a narrow emission line operating at 3.3 µm

Current-tunable diode lasers with narrow emission lines for laser spectroscopy in the 3.2–3.4 µm wavelength range are developed. The lasers, based on an InAsSb/InAsSbP double heterostructure, have a wide-stripe cavity. The wave number increases from 3030 to 3034 cm−1 as the current is raised from 1.5 to 3 times the threshold value at 70 K, while the full width at half-maximum of the laser line decreases from 18 to 10 MHz. It is demonstrated that the linewidth is determined by fluctuations of the cavity resonance frequencies as a result of fluctuations in the concentration of nonequilibrium charge carriers.

Ultimate InAsSbP solid solutions for 2.6–2.8-μm LEDs

Epitaxial layers of phosphorus-rich InAs1−y−xSbyPx solid solutions were obtained by liquid phase epitaxy (LPE). The films with x=0.32 were grown at 575 °C on isoperiodic (100)InAs substrates. It is shown that the growth of InAsSbP layers from a phosphorus-rich liquid phase is accompanied by saturation of the phosphorus content in the solid state. InAsSbP-based diode heterostructures emitting in the 2.6–2.8 μ m wavelength range were obtained, the output emission power of which is sufficient for detecting both natural and industrial gases in the atmosphere.

A tunable single-mode 3.2 μm laser based on an InAsSb/InAsSbP double heterostructure with drive-current tuning range of 10 cm−1

A new type of semi-conductor laser with composition InAsSb/InAsSbP is described. This laser was produced for the absorption spectroscopy of atmospherically important molecules in the 3100 cm(-1) region and tested using a closed-cycle He-cryostat in the temperature range 30-80 K. The optimal characteristics of the laser were found to be a heatsink temperature of 62 K and a drive current range of 50-350 mA. Under these conditions, the laser emits single-mode radiation in an exceptionally large wavenumber range of > 10 cm(-1). To test the laser, several experiments were carried out in which the rovibrational absorption spectra of CH3Cl, NH3, OCS and H2O were measured.

Two-mode diode-laser spectroscopy with a InAsSb/InAsSbP laser near 3.6 µm

The current dependence of the output frequency of InAsSb/InAsSbP diode lasers at wavelengths near 3.6 µm is studied. It is found that in these lasers the number of lasing modes can be reduced without introducing crystallographic defects. It is shown that the photon momentum aids in suppressing the spectral modes closest to the dominant mode. Two-mode laser spectroscopy is done over an interval of 2 cm−1 for two gases, N2O and CH3Cl.

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.

Current and temperature tuning of quantum-well lasers operating in 2.0-to 2.4-µm range

Radiation spectra of GaInAsSb/GaAlAsSb-based quantum-well diode lasers in pulsed and quasi-continuous operation modes were studied in the temperatures range from −10 to +20°C with driving currents varying from 50 to 200 mA. For currents exceeding the threshold value by no more than 30%, a single-mode lasing was usually observed. A further increase in current leads, as a rule, to the appearance of 3–5 additional long-wavelength cavity modes, which suggests the growth of gain in this spectral range due to the interaction of modes. In single-mode conditions, the lasing wavelength is red-shifted with temperature at a rate of 2–3 Å/K because of the current-induced heating of the laser and the corresponding increase in the refractive index. The rate of this heating is estimated at 0.1 µs.

Single-mode fast-tunable lasers for laser-diode spectroscopy

Physical mechanisms leading to the suppression of instability in the electron-hole plasma under conditions of population inversion and, thus, promoting single-mode lasing and drive-current-controlled tuning were studied; in particular, nonuniform injection and spatial oscillations of laser flux were considered. Transient times typical of current-and heat-aided tuning are measured. The effective time constant is estimated as ∼1 µs for heat-controlled tuning; by contrast, it is at least one order of magnitude shorter for current tuning. The tuning range does not exceed several angstroms and is as wide as 100 Å in the case of heat-and current-aided tuning, respectively. A single-mode fast-tunable heterolaser which is capable of operating within the 2.8–3.6 µm wavelength range at 12–120 K and is designed for laser-diode spectroscopy is developed. The results of using the laser for the detection of absorption spectra in OCS, NH3, CH3Cl, CH4, N2O, and H2O vapors are reported.

Emission-line broadening of current tunable InAsSbP/InAsSb/InAsSbP heterostructure lasers

The dependence of emission-line broadening on the drive current was studied at 50–80 K for tunable InAsSbP/InAsSb/InAsSbP double heterostructure lasers operating in the 3.3–3.4 µm spectral region. For a small increase of the injection current I over the threshold current Ith, the line width depends on the I-Ith difference hyperbolically, in accordance with the Schawlow-Townes and Henry theories that assume a homogeneous distribution of the nonequilibrium carrier concentration across the resonator width. With the current raised to (3–4)Ith, line narrowing ceases and the line starts to broaden with increasing current. The observed line broadening is explained by the effect of the nonequilibrium carrier concentration gradient between the middle of the resonator and its edges. In tunable lasers, this gradient increases with current, the lasing wavelength simultaneously decreasing. The minimal width of the lasing line is 10–20 MHz.

High-efficiency 3.4–4.4 μm light-emitting diodes based on a p-AlGaAsSb/n-InGaAsSb/n-AlGaAsSb heterostructure operating at room temperature

Light-emitting diode structures operating at room temperature were obtained based on a p-AlGaAsSb/n-InGaAsSb/n-AlGaAsSb heterostructure with high Al content in the boundary layers formed on a p-GaSb(100) substrate. This structure ensures a threefold increase in the output radiant power and the external quantum yield (∼1%) as compared to the known InAsSb/InAsSbP heterostructure grown on an InAs substrate. A considerable increase in the pulsed output radiant power is explained by a more effective confinement of nonequilibrium charge carriers in the active region and by a decrease in the nonradiative recombination level, which is achieved by creating an isoperiodic structure.