High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring

High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009. Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev.     

Ultimate InAsSbP solid solutions for 2.6–2.8-μm LEDs

Epitaxial layers of phosphorus-rich InAs_1? y ? x Sb _y P _x 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.     

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.     

Flattening of dynamic dielectric phase grating and single-mode lasing under the conditions of transverse oscillations of luminous flux

Emission spectra and the intensity patterns of InAsSbP/InAsSb/InAsSbP-based diode lasers with different cavity lengths and a spectral range of 3–4 μm were studied. It is ascertained experimentally that a 200-to 300-μm-long and 18-μm-wide laser cavity ensures single-mode lasing, during which the wavelengthdecreases with current by about 100 ? and the top of the intensity pattern becomes bimodal, thus indicating that there are transverse spatial oscillations of laser flux in the cavity. In a 300-to 500-μm-long cavity, several tens of modes are generated mainly on the long-wavelength side of the mode that prevailed initially at the lasing threshold and spatial oscillations of laser flux are not observed. Single-mode lasing is attained due to the fact that the transverse oscillations of laser flux flatten the dynamic dielectric phase grating, which is usually produced by the interaction between lasing modes, and prevent an increase in amplification on the long-wavelength side of the dominant mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 11, 2002, pp. 1388–1392. Original Russian Text Copyright ? 2002 by Astakhova, Danilova, Imenkov, Kolchanova, Yakovlev.     

Electroluminescence properties of a whispering-gallery-mode laser with coupled disk cavities

Whispering-gallery-mode (WGM) lasers (emission wavelength λ = 2.1–2.4 μm) with coupled disk cavities connected by a bridge are developed on the basis of a GaInAsSb/GaAlAsSb quantum-well nano-heterostructure and their emission spectra and optical far-field patterns are studied. Almost single-mode lasing in one spatial mode is observed in a wide range of supply currents. The emission wavelength grows with increasing current due to heating of the laser, and this phenomenon can be used in diode-laser spectroscopy. An assumption is made that the flux of generated emission can pass in lasers of this kind from one cavity to the other and back along the cavity-connecting bridge. It is found that strong narrowing of the laser emission pattern occurs with increasing current near the plane separating the coupled cavities.     

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.     

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

InAs/InAs_0.88Sb_0.12/InAs_0.50Sb_0.20P_0.30 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.     

InAsSb/InAsSbP double-heterostructure lasers emitting in the 3–4 µm spectral range

Our earlier reports concerning the fabrication by liquid-phase epitaxy and investigation of InAsSbP/InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm are reviewed. The dependences of spectral characteristics and the spatial distribution of the laser emission on temperature and current are discussed. Lasing modes are shifted by 0.5–1.0 cm⁻¹ to longer wavelengths with increasing temperature. The tuning of the lasing modes by means of current is very fast (10⁻⁸–10⁻¹² s). With increasing current, the modes are shifted to shorter wavelengths by 50–60 ? at 77 K. The maximum mode shift of 104 ? (10 cm⁻¹) is observed at 62 K. The spectral line width of the laser is as narrow as 10 MHz. Abnormally narrow directional patterns in the p-n junction plane are observed in some cases in the spatial distribution of laser emission. The current tuning of lasers, due to nonlinear optical effects, has been modeled mathematically in good agreement with the experiment. Transmittance spectra of OCS, NH₃, H₂O, CH₃Cl, and N₂O gases were recorded using current-tuned lasers. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 12, 2001, pp. 1466–1480. Original Russian Text Copyright ? 2001 by Danilova, Imenkov, Kolchanova, Yakovlev. See [1].     

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 I _th, the line width depends on the I-I _th 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)I _th, 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. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 12, 2000, pp. 1468–1471. Original Russian Text Copyright ? 2000 by Imenkov, Kolchanova, Kubat, Civish, Yakovlev.     

AlGaAsSb lasers emitting in the 1.6 μm region

AlGaAsSb lasers with different Al concentrations in the active and confinement regions are fabricated and investigated. The structures lase in the region ∼1.6 μm. The AlGaAsSb solid solution in the active region is a direct-gap material with a small energy separation (∼56 meV) between the direct-gap Γ minimum and the indirect-gap L minimum of the conduction band. The lasers have a single-mode spectrum with a predominant longitudinal mode in the spatial distribution of the emission. The lasers operate at room temperature in a pulsed mode. Pis’ma Zh. Tekh. Fiz. 25, 35–41 (May 26, 1999)