InP-based Quantum Cascade Lasers Research Articles

Mid-infrared arrayed waveguide gratings using a quantum cascade laser gain medium as core material

Mid-infrared photonics is a widely researched field with several applications, such as chemical sensing and spectroscopy. The development of photonic integrated circuits for the mid-infrared can enable the reduction in device size, weight, and power (SWaP) consumption. This paper demonstrates arrayed waveguide gratings working in the mid-infrared regime (5–5.4 µm). Our devices are fabricated on an InP-based quantum cascade laser platform with the gain medium as the waveguide core. To minimize the propagation losses caused by free carrier absorption and intersubband absorption in the unbiased QCL structure, we exposed the photonic chips to proton implantation. The performance of three sets of AWGs with different etch depths was characterized. The lowest waveguide losses were measured to be 2 dB/cm. The best performing 7×1 AWG and 13×1 AWG designs featured insertion losses of −2dB and −2.5dB, respectively. This study showcases the feasibility of applying such a platform for easy integration with active components like lasers and photodetectors, paving the path for on-chip mid-infrared applications.

High Power, Room Temperature InP-Based Quantum Cascade Laser Grown on Si

We report on the realization of an InP-based long wavelength quantum cascade laser grown on top of a silicon substrate. This demonstration first required the development of an epitaxial template with a smooth surface, which combines two methods of dislocation filtering. Once wafer growth was complete, a lateral injection buried heterostructure laser geometry was employed for efficient current injection and low loss. The laser emits at a wavelength of ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.8~\mu \text{m}$ </tex-math></inline-formula> and is capable of operation above 373 K, with a high peak power (>4 W) at room temperature. Laser threshold behavior with temperature is characterized by a T0 of 178 K. The far field beam shape is single lobed, showing fundamental transverse mode operation.

∼8.5 μm-emitting InP-based quantum cascade lasers grown on GaAs by metal-organic chemical vapor deposition

Room-temperature, pulsed-operation lasing of 8.5 μm-emitting InP-based quantum cascade lasers (QCLs), with low threshold-current density and watt-level output power, is demonstrated from structures grown on (001) GaAs substrates by metal-organic chemical vapor deposition. Prior to growing the laser structure, which contains a 35-stage In0.53Ga0.47As/In0.52Al0.48As lattice-matched active-core region, a ∼2 μm-thick nearly fully relaxed InP buffer with strained 1.6 nm-thick InAs quantum-dot-like dislocation-filter layers was grown. A smooth terminal buffer-layer surface, with roughness as low as 0.4 nm on a 10 × 10 μm2 scale, was obtained, while the estimated threading-dislocation density was in the mid-range × 108 cm−2. A series of measurements, on lasers grown on InP metamorphic buffer layers (MBLs) and on native InP substrates, were performed for understanding the impact of the buffer-layer's surface roughness, residual strain, and threading-dislocation density on unipolar devices such as QCLs. As-cleaved devices, grown on InP MBLs, were fabricated as 25 μm × 3 mm deep-etched ridge guides with lateral current injection. The results are pulsed maximum output power of 1.95 W/facet and a low threshold-current density of 1.86 kA/cm2 at 293 K. These values are comparable to those obtained from devices grown on InP: 2.09 W/facet and 2.42 kA/cm2. This demonstrates the relative insensitivity of the device-performance metrics on high residual threading-dislocation density, and high-performance InP-based QCLs emitting near 8 μm can be achieved on lattice-mismatched substrates.

High-performance quantum cascade lasers at λ ∼ 9 µm grown by MOCVD.

We demonstrate a high power InP-based quantum cascade laser (QCL) (λ ∼ 9 µm) with high characteristic temperature grown by metalorganic chemical vapor deposition (MOCVD) in this article. A 4-mm-long cavity length, 10.5-µm-wide ridge QCL with high-reflection (HR) coating demonstrates a maximum pulsed peak power of 1.55 W and continuous-wave (CW) output power of 1.02W at 293 K. The pulsed threshold current density of the device is as low as 1.52 kA/cm2. The active region adopted a dual-upper-state (DAU) and multiple-lower-state (MS) design and it shows a wide electroluminescence (EL) spectrum with 466 cm-1 wide full-width at half maximum (FWHM). In addition, the device performance is insensitive to the temperature change since the threshold-current characteristic temperature coefficient, T0, is as high as 228 K, and slope-efficiency characteristic temperature coefficient, T1, is as high as 680 K, over the heatsink-temperature range of 293 K to 353 K.

High Power Mid-Infrared Quantum Cascade Lasers Grown on Si

This article details the demonstration of a strain-balanced, InP-based mid-infrared quantum cascade laser structure that is grown directly on a Si substrate. This is facilitated by the creation of a metamorphic buffer layer that is used to convert from the lattice constant of Si (0.543 nm) to that of InP (0.587 nm). The laser geometry utilizes two top contacts in order to be compatible with future large-scale integration. Unlike previous reports, this device is capable of room temperature operation with up to 1.6 W of peak power. The emission wavelength at 293 K is 4.82 μm, and the device operates in the fundamental transverse mode.

High Power Mid-Infrared Quantum Cascade Lasers Grown on GaAs

The motivation behind this work is to show that InP-based intersubband lasers with high power can be realized on substrates with significant lattice mismatch. This is a primary concern for the integration of mid-infrared active optoelectronic devices on low-cost photonic platforms, such as Si. As evidence, an InP-based mid-infrared quantum cascade laser structure was grown on a GaAs substrate, which has a large (4%) lattice mismatch with respect to InP. Prior to laser core growth, a metamorphic buffer layer of InP was grown directly on a GaAs substrate to adjust the lattice constant. Wafer characterization data are given to establish general material characteristics. A simple fabrication procedure leads to lasers with high peak power (&gt;14 W) at room temperature. These results are extremely promising for direct quantum cascade laser growth on Si substrates.

Long wavelength (λ &amp;gt; 13 μm) quantum cascade laser based on diagonal transition and three-phonon-resonance design

An InP-based quantum cascade laser structure emitting at a wavelength of 13.6 μm is proposed and demonstrated. The active region is based on a diagonal transition and three-phonon-resonance design. A 5 mm long, 30 μm wide high-reflection coated device with a double channel ridge waveguide structure has shown a threshold current density of 3.0 kA/cm2, a dynamic range of 4.4 kA/cm2, a peak output power close to 1 W, and an average optical power up to 11.7 mW at 3% duty cycle, at 293 K. The laser shows a characteristic temperature T0 of 314 K and T1 of 336 K over a temperature range from 283 to 313 K.

Broad gain, continuous-wave operation of InP-based quantum cascade laser at λ ∼ 11.8 μm* *Project supported by the National Basic Research Program of China (Grant No. 2018YFA0209103), the National Natural Science Foundation of China (Grant Nos. 61991430, 61774146, 61790583, 61734006, 61835011, 61674144, 61774150, and 61805168), Beijing Municipal Science & Technology Commission, China (Grant No. Z201100004020006), and the Key Projects of

We demonstrate a broad gain, continuous-wave (CW) operation InP-based quantum cascade laser (QCL) emitting at 11.8 μm with a modified dual-upper-state (DAU) and diagonal transition active region design. A 3 mm cavity length, 16.5 μm average ridge wide QCL with high-reflection (HR) coatings demonstrates a maximum peak power of 1.07 W at 283 K and CW output power of 60 mW at 293 K. The device also shows a broad and dual-frequency lasing spectrum in pulsed mode and a maximum average power of 258.6 mW at 283 K. Moreover, the full width at half maximum (FWHM) of the electroluminescent spectrum measured at subthreshold current is 2.37 μm, which indicates a broad gain spectrum of the materials. The tuning range of 1.38 μm is obtained by a grating-coupled external cavity (EC) Littrow configuration, which is beneficial for gas detection.

Observation of the increase in turn-on delay of quantum cascade lasers under pulsed electrical pumping with finite rise time

We demonstrate the experimental measurements of the turn-on delay in InAs-and InP-based quantum cascade lasers operating under pulsed electrical pumping with non-zero rise time. We report the unexpected delay time dependence on the pumping current density, that does not agree with available theoretical predictions. Performed numerical simulation of the model based on rate equations is only in qualitative, but not quantitative, agreement with our observations.

Contactless Measurements of Carrier Concentrations in InGaAs Layers for Utilizing in InP-Based Quantum Cascade Lasers by Employing Optical Spectroscopy.

The precise determination of carrier concentration in doped semiconductor materials and nanostructures is of high importance. Many parameters of an operational device are dependent on the proper carrier concentration or its distribution in both the active area as well as in the passive parts as the waveguide claddings. Determining those in a nondestructive manner is, on the one hand, demanded for the fabrication process efficiency, but on the other, challenging experimentally, especially for complex multilayer systems. Here, we present the results of carrier concentration determination in In0.53Ga0.47As layers, designed to be a material forming quantum cascade laser active areas, using a direct and contactless method utilizing the Berreman effect, and employing Fourier-transform infrared (FTIR) spectroscopy. The results allowed us to precisely determine the free carrier concentration versus changes in the nominal doping level and provide feedback regarding the technological process by indicating the temperature adjustment of the dopant source.

Continuous wave quantum cascade lasers with 5.6 W output power at room temperature and 41% wall-plug efficiency in cryogenic operation

In this paper, we report a post-polishing technique to achieve nearly complete surface planarization for the buried ridge regrowth processing of quantum cascade lasers. The planarized device geometry improves the thermal conduction and reliability and, most importantly, enhances the power and efficiency in continuous wave operation. With this technique, we demonstrate a high continuous wave wall-plug efficiency of an InP-based quantum cascade laser reaching ∼41% with an output power of ∼12 W from a single facet operating at liquid nitrogen temperature. At room temperature, the continuous wave output power exceeds the previous record, reaching ∼5.6 W.

InP-based quantum cascade lasers monolithically integrated onto silicon.

Lasing is reported for ridge-waveguide devices processed from a 40-stage InP-based quantum cascade laser structure grown on a 6-inch silicon substrate with a metamorphic buffer. The structure used in the proof-of-concept experiment had a typical design, including an Al0.78In0.22As/In0.73Ga0.27As strain-balanced composition, with high strain both in quantum wells and barriers relative to InP, and an all-InP waveguide with a total thickness of 8 µm. Devices of size 3 mm x 40 µm, with a high-reflection back facet coating, emitted at 4.35 µm and had a threshold current of approximately 2.2 A at 78 K. Lasing was observed up to 170 K. Compared to earlier demonstrated InP-based quantum cascade lasers monolithically integrated onto GaAs, the same laser structure integrated on silicon had a lower yield and reliability. Surface morphology analysis suggests that both can be significantly improved by reducing strain for the active region layers relative to InP bulk waveguide layers surrounding the laser core.

Room temperature operation of quantum cascade lasers monolithically integrated onto a lattice-mismatched substrate

Experimental data for an InP-based 40-stage quantum cascade laser structure grown on a 6-in. GaAs substrate with a metamorphic buffer are reported. The laser structure had an Al0.78In0.22As/In0.73Ga0.27As strain-balanced active region composition and an 8 μm-thick, all-InP waveguide. High reflection coated 3 mm × 30 μm devices processed from the wafer into a ridge-waveguide configuration with a lateral current injection scheme delivered over 200 mW of total peak power at 78 K with lasing observed up to 170 K. No signs of performance degradation were observed during a preliminary 200-min reliability testing. Temperature dependence for threshold current and slope efficiency in the range from 78 K to 230 K can be described with characteristic temperatures of T0 ≈ 460 K and T1 ≈ 210 K, respectively. Lasing was extended to 303 K by applying a partial high reflection coating to the front facet of the laser.

Transient thermal analysis of semiconductor diode lasers under pulsed operation

Self-heating in semiconductor lasers is often assumed negligible during pulsed operation, provided the pulses are ‘short’. However, there is no consensus on the upper limit of pulse width for a given device to avoid-self heating. In this paper, we present an experimental and theoretical analysis of the effect of pulse width on laser characteristics. First, a measurement method is introduced to study thermal transients of edge-emitting lasers during pulsed operation. This method can also be applied to lasers that do not operate in continuous-wave mode. Secondly, an analytical thermal model is presented which is used to fit the experimental data to extract important parameters for thermal analysis. Although commercial numerical tools are available for such transient analyses, this model is more suitable for parameter extraction due to its analytical nature. Thirdly, to validate this approach, it was used to study a GaSb-based inter-band laser and an InP-based quantum cascade laser (QCL). The maximum pulse-width for less than 5% error in the measured threshold currents was determined to be 200 and 25 ns for the GaSb-based laser and QCL, respectively.

Very low threshold operation of quantum cascade lasers**Project supported by the National Basic Research Program of China (Grant Nos. 2013CB632801 and 2013CB632803), the National Natural Science Foundation of China (Grant Nos. 61306058, 61274094, and 61435014), and the Beijing Natural Science Foundation (Grant No. 4144086).

A strain-compensated InP-based quantum cascade laser (QCL) structure emitting at 4.6 μm is demonstrated, based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy (MBE). By optimizing the growth parameters, a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated. Threshold current densities as low as 0.47 kA/cm2 in pulsed operation and 0.56 kA/cm2 in continuous-wave (cw) operation at 293 K were achieved for this state-of-the-art QCL. A minimum power consumption of 3.65 W was measured for the QCL, uncooled, with a high-reflectivity (HR) coating on its rear facet.

InAs/AlSb quantum cascade lasers operating near 20 µm

InAs-based quantum cascade lasers (QCLs) operating near 20 µm are demonstrated. A double metal waveguide fabricated by transfer of the laser active region onto a host InAs substrate has been employed in these devices. The threshold current density of 1.6 kA/cm2 at 80 K is lower than that of InP-based QCLs emitting in the same spectral region. The lasers operated in pulsed mode up to 170 K.

The effects of injector doping densities on lasing properties of InP-based quantum cascade lasers at 4.3 μm

Effects of the injector doping densities on lasing properties of mid-infrared InAlAs–InGaAs–InP quantum cascade lasers at 4.3μm have been studied. Lasers with different average injector doping between 1.29E17cm−3 and 2.07E17cm−3 have been grown by gas source molecular beam epitaxy (GSMBE), and their lasing characteristics were investigated. Lasers with low doped injectors (1.68E17cm−3) exhibited lower threshold current density, longer emission wavelength and lower characteristic temperature T0. The lower injector doping density decreases waveguide loss. On the other hand, the high doping of the injector increases heat transfer through phonon in QCL active region, and thus results in high characteristic temperature T0.

High power, continuous wave, room temperature operation of λ ∼ 3.4 μm and λ ∼ 3.55 μm InP-based quantum cascade lasers

We report two highly strain-balanced InP-based AlInAs/GaInAs quantum cascade lasers emitting near 3.39 and 3.56 μm. A pulsed threshold current density of only 1.1 kA/cm2 has been achieved at room temperature for both lasers with characteristic temperatures (T0) of 166 K and 152 K, respectively. The slope efficiency is also relatively temperature insensitive with characteristic temperatures (T1) of 116 K and 191 K, respectively. Continuous wave powers of 504 mW and 576 mW are obtained at room temperature, respectively. This was accomplished without buried ridge processing.

Thermal characteristics of InP-based mid-infrared quantum cascade lasers at λ ∼ 8.8 µm

We have theoretically investigated the thermal characteristics of double-channel ridge-waveguide InGaAs/AlInAs quantum cascade lasers (QCLs) emitting at λ ∼ 8.8 µm in comparison with the experimental results. Based on the measured data, the thermal parameters were obtained with heat source densities using a two-dimensional anisotropic heat dissipation model. For 21 µm × 4 mm QCLs, the thermal conductance (G th ) value was 215.5W/K-cm2 at 298 K in continuous-wave (CW) operation. The G th value was significantly increased by using a buried heterostructure (BH) via the regrowth of undoped InP layer around the laser ridge. Also, an additional improvement in the G th was made by the use of a diamond submount, and the temperature dependency of the devices was largely decreased. The G th value was improved to 306.7 W/K-cm2 at 298 K in the CW mode for epilayer-down bonded BH QCLs with an InP embedded layer on a diamond submount.

Coherent quantum cascade laser micro-stripe arrays

We have fabricated InP-based coherent quantum cascade laser micro-stripe arrays. Phase-locking is provided by evanescent coupling between adjacent stripes. Stripes are buried into semi-insulating iron doped InP. Lasing at room temperature is obtained at 8.4μm for stripe arrays comprising up to 16 emitters. Pure supermode emission is demonstrated via farfield measurements and simulations. The farfield pattern shows a dual-lobe emission, corroborating the predicted phase-locked antisymmetric supermode emission.