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We report a study of quantum cascade lasers (QCL), made of InAs and AlSb, operating in the long wavelength mid-infrared range. Lasers based on a design with slightly diagonal intersubband transitions demonstrated improved performances as compared to the previously reported devices employing a vertical scheme. The fabricated lasers operated in the CW regime at 40°C up to a wavelength of 18 μm.

We theoretically and experimentally study the THz electromagnetic properties of an undoped-InAs slab whose permittivity is optically modified by a photo-generation process. The modulation of the permittivity is calculated by solving the ambipolar rate equation for the free carriers. Experiment results demonstrate that InAs is a promising semiconductor to manufacture fast and efficiently on-chip THz components. We show a high modulation of the THz transmission up to 100% from 0.75 to 1.1THz at very low pump fluence in the continuous wave regime. We also demonstrate a high-speed transmission modulation rate up to the MHz range with a modulated pump.

We experimentally and theoretically examined the mode structure of half-disk lasers fabricated by cleaving whispering gallery mode (WGM)-disk lasers. The WGM lasers with a radii R of 50–150 μm emitting near 2.2 μm were fabricated using the GaSb-based quantum well structure [1]. The cleavage usually passes not through the centre of the disk with the deviation δ/R up to 20 % (Fig. 1a). Recently we have demonstrated that in the half-disk lasers the output beam is formed by optical modes located at a distance of 5–20 μm from the disk periphery [2], whereas in the full disk the light propagates along the disk wall, much closer to its edges.

By means of atomic force microscopy (AFM) the spatial mapping of the laser intensity was performed on the cleavage of the whispering gallery modes (WGM) half-disk laser. The study was carried out in the near- and far-field regime. It showed a strong spatial divergence of different modes in the laser.

Novel scanning probe microscopy method of near field imaging of laser radiation is proposed. The method providing a submicron spatial resolution is based on detection of a shift of the probe resonance related to its heating by absorbed radiation. The method has been realized with a conventional silicon probe and has been employed for visualization of infrared emission from a half-disk semiconductor whispering gallery mode laser. Keywords— scanning probe microscopy; near field; laser radiation

Nonresonant tunneling in short-period InAs/AlSb superlattices (SLs) was studied. Several equidistant maxima appeared on current-voltage characteristics of the SLs were shown to be due to the influence of optical cavity on optical transitions within quantum wells (Purcell effect).

A sub-micron process for the fabrication of an original unipolar vertical transport transistor is reported. This allowed suppressing parasitic resistances and achieving high current densities required for THz frequency operation.

We used high hydrostatic pressure techniques to understand the deteriorating temperature performance with decreasing wavelength of short wavelength quantum cascade lasers. Influence of inter-valley scattering and distribution of the electron wave functions will be discussed.

We show that by decreasing the lasing wavelength of InAs/AlSb-based quantum cascade lasers below 3mum, carrier leakage into the L-minimum of conduction band is responsible for their temperature sensitivity and limits their maximum operating temperature.

We report on recent progress in the development of short wavelength InAs/AlSb QCLs: a new short wavelength limit of 2.75 mum and high power, high temperature pulsed operation above 3 mum are demonstrated.

First quantum cascade lasers emitting below 3 mum are demonstrated. The lasers based on the InAs/AlSb material system emit at 2.95-2.97 mum at 83 K and operate up to room temperature.

In this paper InAs/AlSb quantum cascade structures operating at room temperature with peak emission wavelength down to 2.55 /spl mu/m, the shortest emission wavelength of intersubband transitions reported to date. No degradation in structure performances was observed with the emission wavelength decreasing from 4.5 to 2.55 /spl mu/m. The obtained results prove the great potential of the InAs/AlSb system for the development of short wavelength QCLs.

Intersubband electroluminescence from InAs/AlSb quantum cascade structures has been obtained between 2.8 and 3.2 mum up to room temperature with full widths at half maximum of the emission spectra less than 30 meV at 90 K

In this paper we propose and demonstrate a novel approach for improving high frequency performance of InP-based HBTs. A new structure, the Metal Heterojunction Bipolar Transistor (MHBT) where the semiconductor is replaced by a metal in the collector layer is described. This structure not only ensures high dynamic characteristics, but also provides satisfactory static behavior. MHBT demonstrators manufactured for this study show at J/sub c/=30 KA/cm/sup 2/ a current gain cutoff frequency, f/sub T/, of 51 GHz and a maximum oscillation frequency, f/sub max/ of 160 GHz despite their thick base (150 nm) and collector (450 nm) layers. The f/sub max/ value is, for this non-optimized structure, in the range of the best values reported for InP-HBTs. In addition the effective delay time (R/sub c/C/sub BC/)/sub eff/=f/sub T//(8/spl pi/f/sub max//sup 2/) is as small as 78 fs.

In this paper the intrinsic dynamic behavior of the metal heterojunction bipolar transistor (MHBT) is studied. Non-equilibrium electron transport in the base is characterized by electroluminescence. Clear evidence of ballistic transport in MHBT's is shown even at room temperature. The ballistic length is found equal to 17.8 nm in p-InGaAs (N/sub A/=10/sup 19/ cm/sup -3/). Based on these experimental results, an analytical model is developed in order to predict the transit times in both the base and the base-collector space charge layer of the MHBTs.