The room-temperature (300 K), pulsed mode operation of a GaAs-based quantum-cascade laser is presented. This has been achieved by the use of a GaAs/Al0.45Ga0.55As heterostructure which offers the maximum Γ–Γ band offset (390 meV) for this material system without inducing the presence of indirect barrier states. Thus, better electron confinement is achieved, countering the loss of injection efficiency with temperature. These devices show ∼100 K increase in operating temperature with respect to equivalent designs using an GaAs/Al0.33Ga0.67As heterostructure. We also measure 600 mW peak power at 233 K a temperature readily accessible by Peltier coolers.

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The influence of doping density on the performance of GaAs∕AlGaAs quantum-cascade lasers is presented. A fully self-consistent Schrödinger–Poisson analysis, based on a scattering rate equation approach, was employed to simulate the above threshold electron transport in laser devices. V-shaped local field domain formation was observed, preventing resonant subband level alignment in the high pumping-current regime. The resulting saturation of the maximal current, together with an increase of the threshold current, limits the dynamic working range under higher doping. Experimental measurements are in good agreement with the theoretical predictions.

We measured the electronic and lattice temperatures in steady-state operating GaAs/AlGaAs\ud quantum-cascade lasers, by means of microprobe band-to-band photoluminescence. Thermalized\ud hot-electron distributions with temperatures up to 800 K are established. The comparison of our data\ud with the analysis of the temperature dependence of device optical performances shows that the\ud threshold current is determined by the lattice temperature

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The design and operation of quantum cascade (QC) lasers using AlAs/GaAs coupled quantum wells are reported. In this material system, the conduction band offset at the Γ point (∼1 eV) is much higher than in previously reported QC lasers. The use of high band discontinuity allows us to increase the energy separation among the subbands, thus suppressing thermally activated processes which limit device performance at high temperature. The measured thermal characteristics of these promising devices are strongly improved from previously reported GaAs-based QC lasers: The temperature dependence of the threshold current density is described by a very large T0 (320 K) and the laser slope efficiency does not vary for increasing heat sink temperatures. The maximum operating temperature is 230 K, limited by negative differential resistance effects that occur when the applied bias reaches 8 V.

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We report on our magnetotransport measurements of GaAs/GaAlAs quantum cascade structures in a magnetic field of up to 62 T. We observe novel quantum oscillations in tunneling current that are periodic in reciprocal magnetic field. We explain these oscillations as intersubband magnetophonon resonance due to electron relaxation by emission of either single optical or acoustic phonons. Our work also provides a non-optical in situ measurement of intersubband separations in quantum cascade structures. 73.21.Fg,73.43.Qt,85.35.Be,42.55.Px Ever since the pioneering work on the magnetophonon effect by Gurevich and Firsov [1], high magnetic fields have been regarded as an important tool for investigation of the electron-optical-phonon interaction in semiconductor systems, particularly in confined structures. For the in-plane transport, quantization of the carrier motion in the plane into discrete Landau levels (LLs) of energies (N + 1/2)hω c , ω c = eB/m * is the cyclotron frequency, gives rise to quantum oscillations at elevated temperatures due to resonant phonon absorption. These magnetophonon oscillations are periodic in 1/B, and their strength is related to the electron-optical-phonon coupling, while the period gives either the effective mass or the energy of the participating optical phonons [2]. On the other hand, for perpendicular transport the magnetotunneling measurements in double barrier systems have allowed direct probing of the optical-phononassisted transitions from a quasi-two-dimensional (2D) emitter into empty LLs of the central well, as well as determining the effective mass carrier dynamics in these structures [3]. However, little is known from these double barrier studies about intersubband relaxation via opticalphonon emission in quantum wells (QWs). A particularly interesting and unexplored situation occurs when the cyclotron energy exceeds the optical phonon energy and/or the subband energy separation. The first situation is achieved in a GaAs 2D electron gas at magnetic fields above 22 T [2], where the in-plane electron wave function is localized on a scale of the magnetic length, l c = h/eB (3.2 nm at 62 T), and the electron behavior is essentially zero dimensional.Intersubband relaxation via optical phonon emission in quantum wells plays a key role in intersubband radiation sources like the quantum cascade lasers (QCLs) [4]. These systems consist of double-barrier-like structures with three subbands belonging to a central QW structure. When a high bias is applied to the QCL system, the upper subband is populated by tunneling injection. The electron relaxation in the central wells is then essentially governed by the optical phonon emission rate from both upper subbands. As we demonstrate below, the QCL is appropriate to study intersubband relaxation via optical phonon emission. Recently, intersubband relaxation effects were observed in a GaAs/GaAlAs QC structure from both magnetoresistance and and luminescence up to 8 tesla [5]. However, the QCL structure for these studies had intersubband sep...