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We discuss a possibility of achieving population inversion and the associated generation of stimulated terahertz radiation employing transitions between the quantum confinement energy levels of electrons in GaAs/AlGaAs quantum wells under interband photoexcitation. The population inversion occurs between two bottom levels in the conduction band according to a four-level scheme under nonstationary conditions during excitation of electrons from valence band to the top electron state and rapid population of the lower energy level due to processes with the emission of LO-phonons. The time of the depletion of this level due to relatively slow downward energy transitions with the emission of acoustic phonons determines the time interval for the existence of the population inversion, which can amount up to several hundred picoseconds. During this time, the generation of stimulated terahertz radiation is possible at transitions between the two bottom energy levels of electrons in the quantum well.

—The tunneling electron transport in GaAs/AlAs and InAs/AlSb superlattices with electric domains at room temperature is studied. At voltages above the threshold for the formation of domains, a series of maxima on the current–voltage characteristics, almost equidistant in voltage, and current hysteresis during direct and reverse voltage sweeps were found. An explanation is proposed relating the origin of these maxima to tunnel transitions between quantum wells in a triangular domain, assisted by the emission of optical phonons, and hysteresis with a transition between modes with a moving and static domain. The large asymmetry of the transition times between domain modes was found.

Indium arsenide (InAs)-based quantum cascade lasers (QCLs) operating close to 25 µm are reported. Thick n-doped InAs cladding layers were used for optical confinement. Fabry–Perot lasers exhibited a threshold current density as low as 1.1 kA/cm2 in pulsed mode at 80 K. The lasers operated in this regime up to 240 K, where the threshold current density increased up to 1.7 kA/cm2. These are the lowest threshold current densities for QCLs operating above 20 µm.

This work was devoted to the study of stable and unstable optical modes in segment shaped resonators. The size of the studied resonators was much larger than the wavelength of the emitted light, that allowed to use the approaches of geometric optics. It was observed, that with an increase in the δ/R deviation parameter (where δ is the deviation from the center of the half-disk) only a small number of stable spatial modes remain. The possibility of the existence of “sealed” (non-radiating modes) and “open” modes (radiating modes) in resonators of this type was also shown.

Lasers operating on whispering gallery modes (WGMs) and emitting in the mid-IR wavelength range (2.2–2.4 µm) have been created on the basis of coupled semiconductor disk cavities with half-ring contacts. It is established that a separate connection of half-ring contacts of the WGM laser corresponds to a multimode character of radiation, while the connection of all (four) contacts leads to lasing in a single-mode regime. Possible mechanisms of mode synchronization in the proposed WGM lasers are discussed.

The temperature dependence of the threshold current and emission spectra of disk-shaped quantum-well whispering-gallery mode (WGM) lasers is studied in the temperature range of 80–463 K in which the laser emission wavelength increases from 2 to 2.5 μm. It is shown that lasing is observed up to 190°C. Radiative recombination is dominant up to a temperature of 300 K, and nonradiative Auger recombination, in which a recombining electron gives energy to another electron, is so at higher temperatures. The spin-orbit split-off valence subband is not involved in recombination processes, which is attributed to mechanical compression of the quantum-well material.

International audience; The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy

Formation of a natural oxide in ambient atmosphere of the mirrors of a GaSb/GaInAsSb/Ga0.1Al0.9As0.93Sb0.07 laser heterostructure at places of emergence Al-rich layers on the mirror surface is studied. The evolution of topography of the laser mirrors produced by cleavage under ambient and ultrahigh vacuum conditions was studied by AFM and STM for mirrors cleaved. The oxidation of Ga0.1Al0.9As0.93Sb0.07 layers on the mirror surface was monitored for more than a year. It is shown that the oxide layer develops over the course of several months and then attains a constant thickness of about 1 μm. In the course of natural oxidation, the volume of the oxide layer increases, which results in its protrusion above the laser mirror surface approximately by a third of the total thickness of the oxide formed. Ultrahigh vacuum studies ruled out the previously assumed occurrence of the effect of plastic extension of Al-rich layers at the instant of cleavage and the resulting protrusion over the cleavage plane. At the initial stage of oxidation, the oxide protruding above the surface demonstrates an unusual concave region in the upper part, which disappears as the oxide grows further. An explanation of the observed transformation of the shape of the oxide layer is offered. It is assumed that the chemical composition of the oxide varies as its thickness increases.

Single crystalline p-type GaSb was made porous by anodic etching in a hydrofluoric acid solution. The morphology, chemical composition and photoluminescence (PL) of the porous layer were investigated. It has been shown that the porous layer consists of Sb2O3, Ga2O3 and GaSb submicron grains formed during electrochemical etching of GaSb. On the basis of the anodic etching mechanism, it was assumed that the dispersed GaSb nanoscale crystallites are embedded in a transparent oxide matrix. The porous layer exhibited red photoluminescence (PL) at 670–740 nm. The observed short-wavelength PL of the porous samples prepared from GaSb, a narrow band gap semiconductor, is explained by the quantum size effect in the GaSb nanocrystals.

Widely tunable GaInAsSb/AlGaAsSb quantum well (QW) lasers have been grown by molecular beam epitaxy on GaSb substrates. Their emission wavelength, from 2.0 to 2.5 μm, make them suitable for the detection of many gas species in the wavelength range which corresponds to an atmospheric transmission window. Using these devices an experimental setup for open path gas detection has been developed.

We report on the MBE growth and properties of heterostructures and laser diodes based on 4 ML InAs/3 ML GaSb/1 ML InSb/3 ML GaSb short-period superlattices (SPSLs) for emission in the 3–4 μm wavelength range. We show that the interface configuration has a strong influence on both the structural and electronic properties of the SPSL. Excellent agreement between experimental and simulated X-ray diffraction patterns reveals the excellent crystal quality achieved with such complex SPSLs. Lasing is demonstrated up to 300 K in pulsed conditions and up to 200 K under continuous wave operation. Laser emission is centered at 3.32 μm, a technologically very interesting wavelength. Our results demonstrate the potential of these new active zones for mid-IR laser diodes.

Ridge-waveguide laser diodes emitting near 2.38 /spl mu/m have been fabricated from GaInAsSb-GaSb type-II quantum-well (QW) structures grown by molecular beam epitaxy. These devices operated continuous-wave (CW) at room temperature, what is obtained for the first time from a type-II QW laser. At 23/spl deg/C threshold currents in the range 60-140 mA and CW output powers exceeding 1 mW/facet were obtained. These lasers showed a tendency to operate in a single longitudinal mode with a temperature red shift of 0.1 nm//spl deg/C and a current red shift of 0.06 nm/mA.

The molecular beam epitaxy growth of strained (Ga, In)Sb/GaSb quantum wells is investigated. In a narrow range of growth conditions, (Ga, In)Sb quantum well structures exhibiting excellent structural properties as well as intense and narrow photoluminescence transitions are obtained. Stimulated emission at 1.98 m is observed at room temperature from laser diodes with strained quantum wells as the active zone. The lasers exhibit threshold current densities as low as 280 A and a characteristic temperature of 75 K.

GaSb-based heterostructures with strained-layer (x = 0.26 or x = 0.35) single quantum wells and cladding layers were grown by molecular beam epitaxy. The thickness of the GaInSb well was varied from 3.0 to 14.5 nm. Intense room-temperature electroluminescence was observed from mesa diodes with peak emission wavelengths in the spectral range. The dependence of emission energy on well thickness is consistent with the predictions obtained by an effective mass treatment assuming a rectangular type I quantum well and a conduction band offset .

International audience; Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated by atomic resolution scanning transmission electron microscopy. Experimental strain profiles were compared to those coming from a model structure. High negative out-of-plane strains with the same order of magnitude as perfect Al-As interfaces were observed. The effects of the geometrical phase analysis used for strain determination were evidenced and discussed in the case of abrupt and huge variations of both atomic composition and bond length as observed in these interfaces. Intensity profiles performed on the same images confirmed that changes of chemical composition are the source of high strain fields at interfaces. The results show that spontaneously assembled interfaces are not perfect but extend over 2 or 3 monolayers.

We have investigated the spontaneous emission from InAs/GaSb quantum wells grown by molecular beam epitaxy. A strong photoluminescence signal was observed only from samples grown in a narrow substrate temperature range around 400 °C with InSb-like interfaces. From an analysis of the photoluminescence energy with the excitation density, we demonstrated the formation of triangular quantum wells for holes in the GaSb barriers close to the interfaces. Finally, the temperature dependence of the photoluminescence peak energy showed a deviation from the InAs band gap evolution at low temperature, which could be related to the type II broken gap band alignment.

Ga/sub 0.88/In/sub 0.12/As/sub 0.10/Sb/sub 0.90//Al/sub 0.47/Ga/sub 0.53/As/sub 0.04/Sb/sub 0.96/ double heterostructure lasers emitting at 2.05 mu m have been grown by liquid phase epitaxy on GaSb substrates. For pulsed operation of 300 mu m wide broad stripe lasers, output power as high as 80 mW per facet and threshold current density as low as 1.7 kA/cm/sup 2/ have been obtained for cavity lengths of 300 and 900 mu m respectively. Mesa-stripe lasers 200 mu m long showed room temperature threshold current of 200 mA with a characteristic temperature T/sub 0/=115 K.

Room temperature, tunable, external-cavity short-wavelength InAs/AlSb quantum cascade laser (QCL) is reported. Wavelength tuning of 85 nm for the spectral range between 3190 nm and 3275 nm has been achieved by rotating the diffraction grating forming the external cavity. To suppress lasing inside the QCL cavity, its ridge was tilted by 7° at the external cavity end. The optimal tilting angle of the laser ridge was chosen by careful consideration of the return losses of the TM-polarized waveguide mode from the diffraction grating in a quasi-Littrow configuration and the Fabry-Perot feedback from the tilted laser facet. No antireflection coating was used.

Quantum cascade lasers (QCLs) emitting at wavelengths as short as 2.63–2.65 μm are demonstrated. The InAs/AlSb QCL design was optimized to weaken carrier leakage into the L-valley by reducing coupling between the active InAs quantum wells. The lasers with HR-coated facets operated up to 175 K.

We present a study of the structural and optical properties of a heterostructure emitting in the midinfrared. The structure consists of monolayerlike InSb quantum wells inserted in an InAs/GaSb superlattice (SL) matrix. X-ray diffraction and transmission electron microscopy analyses show a high structural quality of the structure. A strong emission line with a peak energy near 0.30 eV (3.5 mu m) is observed from the monolayerlike InSb. In order to identify the physical origin of this transition, excitation density and temperature dependent photoluminescence experiments have been performed on samples with different nominal InSb thicknesses and SL designs. The experimental results suggest a type II band alignment, with electrons localized in the conduction miniband of the InAs/GaSb SL matrix and holes localized in the monolayerlike InSb. This assignment is supported by the shift of InSb layer emission to lower energies when the SL design is changed, and by tight-binding calculations. (C) 2008 American Institute of Physics.

International audience; The InAs/AlSb material system is a promising candidate for the development of short wavelength quantum cascade lasers because of the large conduction band offset of 2.1 eV. In this letter, we present a study of room temperature electroluminescence of InAs/AlSb quantum cascade structures as a function of the emission wavelength. Intersubband emission with a transition energy of 500 meV (λ=2.5 μm) has been obtained.

A study of the effects of the injected current and the thermal resistance on the tunability of antimonide-based diode lasers is presented. The studied diode lasers, emitting at around 2.3 µm, are dedicated to gas detection in the atmosphere, based on tunable-diode-laser absorption spectroscopy (TDLAS). This very useful technique requires, from the lasers, an emitted tunable wavelength able to cross a gas absorption line to detect the absorbed light. Typically a tuning rate of a few GHz/mA is sufficient to perform gas detection at atmospheric pressure (Vicet et al., 2002). It is then important to know and understand the tuning properties of the devices to achieve gas detection. They are very sensitive to thermal effects which are involved in all tuning processes. The lasers studied are shown to be well adapted to gas detection, paradoxically because of their large thermal resistance Rth which increases Joule heating, and mainly affects their tunability.

Narrow ridge 5 /spl mu/m-wide GaInSbAs/GaAlSbAs quantum well (QW) lasers emitting in the continuous wave (CW) regime at temperatures up to 130/spl deg/C have been fabricated. The CW threshold current varied between 20 and 35 mA at room temperature (RT). The lasers operated in the fundamental spatial mode and exhibited single longitudinal mode emission over a wide range of CW operation conditions. The emission wavelength increased from 2.26 /spl mu/m at RT up to 2.43 /spl mu/m at 124/spl deg/C. The CW output optical power reached 45 mW/facet at 22/spl deg/C and exceeded 10 mW/facet at 100/spl deg/C.

Monolithic Sb-based vertical cavity surface emitting lasers (VCSELs) operating near 2.2 /spl mu/m at room temperature have been successfully fabricated and characterised. A pulsed output optical power of 20 mW has been achieved, the threshold current density being 2 kA/cm/sup 2/ for 200 /spl mu/m diameter devices. The entire structure was grown in a single growth run using molecular beam epitaxy.

Powerful mid-infrared (1.7-4.8 /spl mu/m) light emitting diodes were manufactured by liquid phase epitaxy using GaSb-InAs compounds. Their output optical power was enhanced up to 2-3.5 mW using symmetrical double heterostructures with large band offsets. These diodes can be used as narrow bandwidth emitters for cost-reduced setups for atmospheric pollution monitoring.

Laser emission is reported for the first time from a 10 monolayer-wide highly strained (3.2%) InAs single quantum well confined by Ga/sub 0.47/In/sub 0.53/As layers. At 80 K the emission spectrum of broad-area laser diodes is centred at 1.836 mu m, the threshold current-density is approximately 500 A/cm/sup 2/ and the characteristic temperature is T/sub 0/ approximately=30 K. CW operation is achieved up to 110 K with narrow-stripe devices but at shorter wavelength, due to increased losses and filling of the quantum-well energy levels.