Arkadiy Lyakh

λ~7.1 μm quantum cascade lasers with 19% wall-plug efficiency at room temperature

Strain-balanced In0.6Ga0.4As/Al0.56In0.44As quantum cascade lasers emitting at a wavelength of 7.1 μm are reported. The active region is based on a three-phonon-resonance quantum design with a low voltage defect of 120 meV at injection resonance. A maximum wall-plug efficiency of 19% is demonstrated in pulsed mode at 293 K. Continuous-wave output power of 1.4 W and wall-plug efficiency of 10% are measured at the same temperature, as well as 1.2 W of average power in uncooled operation. A model for backfilling of the lower laser level which takes into account the number of subbands in the injector is presented and applied to determine the optimum value of the voltage defect to maximize wall-plug efficiency at room temperature, which is found to be ~100 meV, in good agreement with experimental results.

Tapered 4.7 μm quantum cascade lasers with highly strained active region composition delivering over 4.5 watts of continuous wave optical power

A strain-balanced, Al0.7In0.22As/In0.72Ga0.28As/InP quantum cascade laser structure, designed for light emission at 4.7µm using the non-resonant extraction design approach, was grown by molecular beam epitaxy. Laser devices were processed in tapered buried heterostructure geometry and then mounted on AlN/SiC composite submounts using hard solder. A 10 mm long laser with 7.5µm-wide central section tapered up to 20µm at laser facets generated over 4.5W of single-ended CW/RT optical power at 283K. Maximum wallplug efficiency of 16.3% for this laser was reached at 4W level. Reliability of over 2,000h has been demonstrated for an air-cooled system delivering optical power of 3W in a collimated beam with overall system efficiency exceeding 10%.

Long-Wave IR Quantum Cascade Lasers for emission in the λ = 8-12μm spectral region

In this article we review a selection of recent results on long-wave quantum cascade lasers both for high power and for single-mode emission. Both MBE-grown and MOCVD-grown devices are examined and compared. Currently, LWIR QC lasers exhibit output powers in the Watt-level range and up to double-digit conversion efficiencies in the best cases.

Substrate-emitting, distributed feedback quantum cascade lasers

By using a semiconductor/metal grating formed on the episide of a quantum-cascade structure, distributed feedback lasing has been achieved with beam emission through the substrate. Using short-pulse excitation (100ns, 16kHz), single-longitudinal-mode operation near 5.1μm is demonstrated over wide ranges in heatsink temperature and drive current. The beam divergence in the longitudinal direction at a distance 40cm away from the 2.5mm wide aperture is ∼0.5°.

Progress in high-performance quantum cascade lasers

Because of their compact size, reliability, tunability, and convenience of direct electrical pumping, quantum cascade lasers have found a number of important civilian and defense applications in the midwave infrared and long-wave-infrared spectral range. Most of these applications would benefit from higher laser optical power and higher wall-plug efficiency. We describe some of the most important features of high-efficiency quantum cascade laser design and realization of high-power quantum cascade laser systems. Specifically, optimization of the active region and waveguide, thermal management on the chip level, and impact of the laser facet coating on laser efficiency and scaling of optical power with cavity length are discussed. Also, we present experimental results demonstrating multiwatt operation with reliability of at least several thousands of hours on a system level.

Continuous wave operation of buried heterostructure 4.6µm quantum cascade laser Y-junctions and tree arrays

Room-temperature continuous-wave operation for buried heterostructure 4.6 µm quantum cascade laser Y-junctions and tree arrays, overgrown using hydride vapor phase epitaxy, has been demonstrated. Pulsed wall plug efficiency for the Y-junctions with bending radius of 5mm was measured to be very similar to that of single-emitter lasers from the same material, indicating low coupling losses. Comparison between model and experimental data showed that the in-phase mode was dominating for 10mm-long Y-junctions with 5 µm-wide 1mm-long stem and 5 µm-wide branches. Total optical power over 1.5 W was demonstrated for four-branch QCL tree array.

Room-temperature, mid-infrared (λ=4.7μm) electroluminescence from single-stage intersubband GaAs-based edge emitters

GaAs-based, single-stage, intersubband devices with active regions composed of deep quantum wells (i.e., In0.3Ga0.7As) and high AlGaAs barriers display strong room-temperature emission at λ=4.7μm. The structures are grown by metalorganic chemical vapor deposition. The large energy barriers (∼360meV) for electrons in the upper energy level of the active region strongly suppress both the carrier leakage as well as the tunneling escape rate out of the wells. As a result, the ratio of emissions at 80 and 300K is as low as 2.0, and thus there is considerably less need for a Bragg mirror/transmitter-type region. Devices with virtually 100% tunneling injection efficiency have been realized, and their room-temperature spectra are narrow: 25meV full width at half maximum. These deep-well, single-stage structures are intended for use as the emitting units in two-dimensional, intersubband quantum-box lasers, or as the stages of quantum-cascade lasers for efficient, room-temperature operation in the 3–5-μm wavelength...

Narrow stripe-width, low-ridge high power quantum cascade lasers

Narrow stripe-width, low-ridge quantum cascade lasers operating at 5.3μm were fabricated from InP-based, metal-organic chemical-vapor-deposition-grown material. Maximum peak-pulsed output power of 12W at 14A was measured from a low-ridge laser with a high reflectivity coated back facet. Modeling shows that the lateral variation of the transverse conductivity is essential for an accurate description of the current spreading in these devices.

High power, high efficiency quantum cascade laser systems for directional infrared countermeasures and other defense and security applications

We present our latest results on the development of high power, high efficiency room temperature quantum cascade lasers. Strain-balanced, InP-based quantum cascade structures, designed for light emission at 4.6 μm using a new non-resonant extraction design approach, were grown by molecular beam epitaxy and processed as buried heterostructure lasers. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of 5 mm by 11.6 μm mounted on diamond submounts. Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and 0.86 kA/cm2. 7 mm-long, 8.5 μm-wide devices mounted on aluminum nitride submounts with optimized reflectivity coatings on the output facet emitted 2.9 W under the same conditions and 1.2 W in uncooled pulsed operation. Leveraging this research, we developed fully packaged, air-cooled, table-top turn-key laser systems delivering in excess of 2 W of collimated continuous-wave radiation. The high performance and level of device integration make these quantum cascade lasers the primary choice for various defense and security applications, including directional infrared countermeasures, mid-wave infrared illuminators and free space optical communications.

Gallium–Arsenide-Based Bipolar Cascade Lasers With Deep Quantum-Well Tunnel Junctions

Edge-emitting GaAs-based lasers were fabricated from metal-organic chemical vapor deposition-grown material containing two diode laser structures separated by a quantum-well tunnel junction (QWTJ). The QWTJ was comprised of a thin, high indium content InGaAs layer sandwiched between relatively low-doped p-type and n-type GaAs layers. Comparison of near-field data with predictions from a one-dimensional current spreading model and comparison of current-voltage characteristics for these two-stage or double-stage lasers (DSLs) with single-stage lasers (SSLs) shows that this type of reverse-biased QWTJ has a low effective resistivity. As a consequence, current spreading perpendicular to the laser length in the plane of the layers (lateral direction) is reduced leading to a relatively low threshold current density for the second stage. In addition, the differential quantum efficiency of these DSLs is nearly twice that of SSLs