D. G. Revin

InGaAs∕AlAsSb∕InP quantum cascade lasers operating at wavelengths close to 3μm

The authors report the realization of short wavelength (3.05μm⩽λ⩽3.6μm) InP lattice-matched In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum cascade lasers (QCLs). The highest-performance device displays pulsed laser action at wavelengths between 3.4 and 3.6μm, for temperatures up to 300K, with a low temperature (80K) threshold current density of approximately 2.6kA∕cm2, and a characteristic temperature of T0∼130K. The shortest wavelength QCL (λ≈3.05μm) has a higher threshold current density (∼12kA∕cm2 at T=20K) and operates in pulsed mode at temperatures up to 110K.

Room temperature operation of InAs∕AlSb quantum cascade lasers

The room temperature operation of InAs∕AlSb quantum cascade lasers is reported. The structure, grown by molecular beam epitaxy on an InAs substrate, is based on a vertical transition design and a low loss n+-InAs plasmon enhanced waveguide. The lasers emitting near 4.5μm operate in pulse regime up to 300K. The threshold current density of 3.18-mm-long lasers is 1.5kA∕cm2 at 83K and 9kA∕cm2 at 300K.

λ∼3.1 μm room temperature InGaAs/AlAsSb/InP quantum cascade lasers

Strain compensated In0.67Ga0.33As/AlAs0.8Sb0.2/InP quantum cascade lasers emitting at wavelengths near 3.1 μm at room temperature have been demonstrated. The lasers operate in pulsed mode with threshold current density of 3.6 kA/cm2 at 80 K and 19.2 kA/cm2 at 295 K. The peak optical power for an as-cleaved 3 mm long and 10 μm wide ridge device exceeds 1 W per facet at 80 K and is around 8 mW at 295 K. The observed laser performance suggests that room temperature operation for these lasers remains possible beyond the predicted threshold for Γ-L intervalley scattering of electrons in the upper laser levels.

Quantum cascade lasers grown by metalorganic vapor phase epitaxy

We report the growth of GaAs-based quantum cascade lasers using atmospheric pressure metalorganic vapor phase epitaxy. The necessary control of interface abruptness and layer thickness uniformity throughout the structure has been achieved using a horizontal reactor in combination with individually purged vent/run valves. A low-temperature threshold current density of 10 kA/cm2 and maximum operating temperature of 140 K have been measured. These performance levels are comparable with early GaAs-based devices grown using molecular-beam epitaxy. The measured emission wavelength (λ∼11.8 μm) is approximately 3-μm longer than the calculated transition wavelength, which we explain using a model incorporating compositional grading of the active region barriers.

Broadband 6μm<λ<8μm superluminescent quantum cascade light-emitting diodes

Midinfrared emission from intersubband superluminescent light-emitting diodes is reported. We have obtained broadband emission spectra at around 7μm with a full width at half maximum of ∼2μm, using quantum-cascade-laser active regions designed to emit at 11 different wavelengths simultaneously. By introducing additional mirror loss in the Fabry–Perot resonator using just a single cleaved facet, with the other mirror formed by wet etching, the laser threshold current is significantly increased and superlinear light-current characteristics are observed. Optical peak powers of several tens of μW are measured at low temperatures.

Dispersive gain and loss in midinfrared quantum cascade laser

We report the measurements of dispersive gain (simultaneous coexistence of gain and losses on a single intersubband transition) in a quantum cascade laser. Broadband transmission spectra through the waveguide of a λ∼4.7μm In0.53Ga0.47As∕AlAs0.56Sb0.44∕InP quantum cascade laser have been studied at a bias below laser threshold and at different temperatures. For a certain range of current, and at temperatures higher than about 150K, the transmission spectra show clear dispersive gain/loss behavior with the possibility for intersubband gain to be observed even without global population inversion between laser levels.

λ∼4-5.3 μm intersubband emission from InGaAs-AlAsSb quantum cascade structures

The In0.53Ga0.47As–AlAs0.56Sb0.44 materials system, lattice matched to InP, is an attractive candidate for short wavelength quantum cascade lasers due to the very large conduction band discontinuity (∼1.6 eV) and compatibility with well established quantum cascade laser waveguide design and fabrication technology. In this letter we report the operation of In0.53Ga0.47As–AlAs0.56Sb0.44 quantum cascade structures emitting in the wavelength range λ∼4–5.3 μm. Clear intersubband electroluminescence peaks are observed close to the design wavelengths, with full widths at half maximum in the range of ∼30–40 meV.

InGaAs∕AlAsSb∕InP strain compensated quantum cascade lasers

The authors demonstrate the feasibility of strain compensated InGaAs∕AlAsSb∕InP quantum cascade lasers (QCLs). Three QCL structures have been investigated, having identical design but with different indium fractions in InxGa1−xAs quantum wells: 0.53 (lattice matched reference device), 0.6, and 0.7. All lasers display similar operating characteristics at λ≈4.1μm with no degradation of performance for the strain compensated devices. This strain compensated system is of interest for QCLs at λ<∼3.5μm. It provides increased energy separation between the Γ and X conduction band minima in the quantum wells, thus decreasing carrier leakage from the upper laser levels by intervalley scattering.

Room-Temperature Operation of Discrete-Mode InGaAs–AlAsSb Quantum-Cascade Laser With Emission at

Discrete-mode quantum-cascade lasers have been developed in the InGaAs-AlAsSb-InP materials system. For an uncoated 10-μ m-wide ridge waveguide and 3000-μm-long cavity, the laser had a threshold current density J_th of 4.2 kA·cm^-2 (I_th=1.5 A) at 300 K with a slope efficiency of 80 mW/A. A stable single-mode emission near 3.3 μ m with a sidemode suppression ratio of nearly 25 dB was observed and a tuning coefficient of 0.22 nm/K was obtained in the temperature range of 253 K <; T <; 303 K.

\lambda=3.3\ \mu

We present a hybrid, mid-infrared metamaterial device, consisting of a near-surface semiconductor quantum well beneath a gold split ring resonator array. Electrical control of the free carrier concentration in the near-surface quantum well allows variation of the refractive index within the fringing field of the split ring resonator array. We observe a 10% transmission change at the fundamental resonance of the split ring resonators, in very good agreement with simulations. For optimised structures, we predict a 10% wavelength shift of the fundamental resonance, with important implications for optical components such as switches and spatial light modulators.