InP-based Quantum Cascade Lasers Research Articles

Highly temperature insensitive quantum cascade lasers

An InP based quantum cascade laser (QCL) heterostructure emitting around 5 μm is grown with gas-source molecular beam epitaxy. The QCL core design takes a shallow-well approach to maximize the characteristic temperatures, T0 and T1, for operations above room temperature. A T0 value of 383 K and a T1 value of 645 K are obtained within a temperature range of 298–373 K. In room temperature continuous wave operation, this design gives a single facet output power of 3 W and a wall plug efficiency of 16% from a device with a cavity length of 5 mm and a ridge width of 8 μm.

Evaluation of injectorless quantum cascade lasers by combining XRD- and laser-characterisation

We present a wavelength prediction procedure on the basis of X-ray measurements and simulations for InP-based injectorless quantum cascade laser (QCL) devices. These lasers show excellent performance in the mid-infrared wavelength range, but are very sensitive to growth deviations, which cause strong wavelength shifts and are a serious obstacle for applications like gas sensing. However, by XRD-simulations of the active region, which consists of InAs, AlAs, GaInAs and AlInAs, the thicknesses and compositions can be extracted and are used as input values for bandstructure calculations, so that a prediction for the resonance energy of the laser transition can be obtained. With this technique a wavelength evaluation of injectorless QCLs with 3% accuracy could be accomplished, which is an essential improvement in applications like gas sensing.

High-performance InP-based midinfrared quantum cascade lasers at Northwestern University

We present recent performance highlights of midinfrared quan- tum cascade lasers (QCLs) based on an InP material system. At a repre- sentative wavelength around 4.7 μm, a number of breakthroughs have been achieved with concentrated effort. These breakthroughs include watt-level continuous wave operation at room temperature, greater than 50% peak wall plug efficiency at low temperatures, 100-W-level pulsed mode operation at room temperature, and 10-W-level pulsed mode oper- ation of photonic crystal distributed feedback quantum cascade lasers at room temperature. Since the QCL technology is wavelength adaptive in nature, these demonstrations promise significant room for improvement across a wide range of mid-IR wavelengths. C 2010 Society of Photo-Optical

Watt level performance of quantum cascade lasers in room temperature continuous wave operation at λ∼3.76 μm

An InP-based quantum cascade laser heterostructure emitting at 3.76 μm is grown with gas-source molecular beam epitaxy. The laser core is composed of strain balanced In0.76Ga0.24As/In0.26Al0.74As. Pulsed testing at room temperature exhibits a low threshold current density (1.5 kA/cm2) and high wall plug efficiency (10%). Room temperature continuous wave operation gives 6% wall plug efficiency with a maximum output power of 1.1 W. Continuous wave operation persists up to 95 °C.

3 W continuous-wave room temperature single-facet emission from quantum cascade lasers based on nonresonant extraction design approach

A strain-balanced, InP-based quantum cascade laser structure, designed for light emission at 4.6 μm using a new nonresonant extraction design approach, was grown by molecular beam epitaxy. Removal of the restrictive two-phonon resonant condition, currently used in most structure designs, allows simultaneous optimization of several design parameters influencing laser performance. Following the growth, the structure was processed in buried heterostructure. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of 5 mm×11.6 μm. Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and 0.86 kA/cm2.

Current- and Temperature-Induced Beam Steering in 7.8-${\mu}$m Emitting Quantum-Cascade Lasers

We report large current- and temperature-induced beam-steering effects, observed in the far-field distribution of InP-based quantum-cascade lasers emitting around 7.8-mum wavelength operated in pulsed mode. Changing the temperature within a narrow range of ~10degC around room-temperature leads to a change in the direction of the output beam, as given by the central lobe in the far-field intensity distribution, from +11deg to -13deg as measured relative to the resonator axis. This beam steering effect is linked to changes in the lateral mode distribution, as revealed by time-resolved spectroscopy of the lasing spectrum.

Intervalley carrier transfer in short-wavelength InP-based quantum-cascade laser

The scattering of electrons out of the upper laser state into indirect valleys in quantum-cascade lasers is demonstrated by investigating the operation of the laser under the influence of magnetic fields up to 45 T. A quantum-cascade laser based on strain-compensated AlAs barriers and In0.73Ga0.27As/InAs wells, emitting with wavelength 3.1 μm, is investigated as a function of magnetic field normal to the surface. Minima in emission power are observed when Landau levels of the upper laser state are brought into resonance with states derived from the indirect valleys, leading to the partial depopulation of the upper laser level. The energy for the indirect valley states is determined to be about 640 meV above the bottom of the In0.73Ga0.27As Γ valley, about 70 meV above the upper laser level.

Room temperature continuous wave operation of quantum cascade lasers with 12.5% wall plug efficiency

An InP based quantum cascade laser heterostructure emitting at 4.6μm was grown with gas-source molecular beam epitaxy. The wafer was processed into a conventional double-channel ridge waveguide geometry with ridge widths of 19.7 and 10.6μm without semi-insulating InP regrowth. An uncoated, narrow ridge device with a 4.8mm cavity length was epilayer down bonded to a diamond submount and exhibits 2.5W maximum output power with a wall plug efficiency of 12.5% at room temperature in continuous wave operation.

1.6 W high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 4.6μm

A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.

Impact of doping on the performance of short-wavelength InP-based quantum-cascade lasers

The effect of doping concentration on the performance of short-wavelength quantum-cascade lasers based on the strain-compensated InGaAs/InAlAs/AlAs heterostructure on InP, emitting at 3.8 μm, is investigated for average doping concentrations between 0.3 and 3.9×1017 cm−3 (sheet densities between 1.6 and 20.9×1011 cm−2). Although the threshold current density is rather independent of doping concentration, the maximum current density increases with doping and exhibits a saturation for the highest doping level. Other important performance characteristics such as differential quantum efficiency, peak optical emission power, slope efficiency, and maximum operating temperature are observed to be maximized for structures with an average doping of 2−3×1017 cm−3, corresponding to a sheet density of about 1.5×1012 cm−2.

Fe-implantation for rear-facet coatings of InP-based quantum cascade lasers

Fe-implantation is used to create a high-resistivity layer at the rear facet of an InP-based quantum cascade laser (λ=3.9 µm), subsequently coated with a metallisation of Cr (5 nm) and Au (200 nm). The coatings lead to a 3.7-fold increase of front-facet power and a 20–30% reduction in threshold current density compared to uncoated lasers.

Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency

The authors report on the development of λ∼4.7μm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150K, with continuous-wave output powers of more than 1W.

Second harmonic generation in (111)-oriented InP-based quantum cascade laser

We show the realization of quantum cascade lasers (QCL) grown on (111)-oriented InP substrates instead of the usual (100)-oriented surface. Growth along [111] orientation allows the excitation of the nonlinear susceptibility for the transverse magnetic wave produced by the QCL. Two devices were realized, at 6 and 10 μm wavelengths. They are compared with the same structures grown on the usual (100)-oriented surface. Second harmonic generation is demonstrated in one of the devices.

Key issues associated with low threshold current density for InP-based quantum cascade lasers

A set of room temperature low threshold current densities of a mid-infrared InP-based quantum cascade lasers (QCLs) have been demonstrated. Threshold current densities as low as 1.7 kA/cm 2 for multi-mode Fabry-Perot QCLs at an emission wavelength of 7.6 μm and 0.9 kA/cm 2 for single-mode distributed feedback QCLs at an emission wavelength of 7.7 μm have been achieved at 300 K. The results obtained are through the precision control of doping incorporation and concentration, the active region of the structure for suppressing the current leakage, and the low resistance material choice in the wave guide cladding and plasmon for improving heat dissipation.

High performance InP-based quantum cascade distributed feedback lasers with deeply etched lateral gratings

The fabrication and operating characteristics of lateral grating distributed feedback InP-based quantum cascade lasers emitting at λ∼10μm are reported. High performance, room temperature single mode lasers, utilizing double-sided lateral gratings, are achieved in InP-based material grown by metal organic phase epitaxy. These deeply etched gratings are made possible by the development of a high aspect ratio, multistage, inductively coupled plasma etch process. A threshold current density of ∼5.5kA∕cm2 is measured at room temperature and side mode suppression ratio >20dB with a tuning coefficient of −0.067cm−1K−1 is observed over a temperature range of 190–330K.

Influence of Injector Doping Concentration on the Performance of InP-Based Quantum-Cascade Lasers

The influence of injector doping concentration Ninj on the performance of InP-based quantum-cascade (QC) lasers is investigated for devices emitting around 9.2-mum wavelength and injector doping concentrations between 1times1017 cm-3 and 3times1017 cm-3. The threshold current density, the dynamic range, the maximum emitted output power as well as the maximum operating temperature are found to increase with increasing N inj. All in all, there exists no optimal value of Ninj per se. In fact, the injector doping concentration has to be adjusted individually depending whether emphasis is placed on obtaining low threshold current densities or on high-power operation

Low-threshold room-temperature operation of injectorless quantum-cascade lasers: influence of doping density

The influence of the doping density in the active sections of InP-based injectorless quantum cascade lasers, emitting at 6.8 µm, is investigated. The doping sheet density is varied in the range 2.5–8.6×1010 cm−2. Lasing is observed in the whole range, with a threshold current density as low as 1.2 kA/cm2 at 300 K for the smallest doping sheet density of 2.5×1010 cm−2. Further improvement has been made by additionally increasing the number of periods in the active region from 40 to 60. With the same doping level of 2.5×1010 cm−2 record low threshold current densities of 0.73 kA/cm2 at 300 K were achieved.

High-power spatial singlemode quantum cascade lasers at 8.9 [micro sign

High performance of InP-based quantum cascade lasers emitting at λ≃9 µm is reported. A thick electroplated gold layer was deposited on top of the laser to improve heat dissipation. Devices with one facet high reflection coated produce a maximum output power of 175 mW at 40% duty cycle at room temperature and continuous-wave operation up to 278 K.

Non-equilibrium electronic distribution within one period of InP-based quantum cascade lasers

A joint theoretical and experimental investigation on the influence of the doping concentration in InP-based quantum cascade lasers on the device performance is presented. The theoretical analysis is based on a Monte Carlo simulation that includes both electron–phonon and electron–electron scattering and explicitly considers non-equilibrium phonon effects. Good agreement is found between the experimental data and the Monte Carlo results, which clarify the role played by doping in the alignment of the electron levels and in the achievement of population inversion.

MOVPE grown quantum cascade lasers

We report the metal-organic vapour phase epitaxy growth of quantum cascade lasers (QCLs) in both the GaAs–AlGaAs and InGaAs–AlInAs–InP materials systems. The GaAs based sample shows an increased emission wavelength relative to an equivalent design grown by molecular beam epitaxy, which we attribute to interfacial grading in the metal-organic vapour phase epitaxy device. The InP-based QCL (λ≈8.5 μm) operates in pulsed mode at room temperature, with low temperature threshold current density ∼1500 A/ cm 2 . This performance is comparable with that previously reported for similar structures grown by molecular beam epitaxy. The high quality interfaces necessary for successful QCL operation are achieved by using individually purged vent/run valves in the gas-handling section of the reactor, as well as a low growth rate for the active region of the structure.