In this paper, we report the growth of high-quality In0.59Ga0.41As/In0.37Al0.63As strain-balanced quantum cascade lasers (QCLs) in the low-pressure MOCVD production type multi-wafer planetary reactor addressing, in particular, quality and scaled manufacturing issues. Special attention was given to achieving the sharp interfaces (IFs), by optimizing the growth interruptions time and time of exposure of InAlAs layer to oxygen contamination in the reactor, which all result in extremely narrow IFs width, below 0.5 nm. The lasers were designed for emission at 7.7µm. The active region was based on diagonal two-phonon resonance design with 40 cascade stages. For epitaxial process control, the High Resolution X-Ray Diffraction (HR XRD) and Transmission Electron Microscopy (TEM) were used to characterize the structural quality of the QCL samples. The grown structures were processed into mesa Fabry-Perot lasers using dry etching RIE ICP processing technology. The basic electro-optical characterization of the lasers is provided. We also present results of Green’s function modeling of QCLs and demonstrate the capability of non-equilibrium Green’s function (NEGF) approach for sophisticated, but still computationally effective simulation of laser’s characteristics. The sharpness of the grown IFs was confirmed by direct measurements of their chemical profiles and as well as the agreement between experimental and calculated wavelength obtained for the bandstructure with ideally abrupt (non-graded) IFs.

QCLs were first demonstrated in 1994. Since then, they have undergone fast development, both in terms of device maturity as well as new field of basic science, enabling the developments in various fields of research. Quantum Cascade Lasers are essential sources for IR photonics providing narrow linewidth and sufficient wavelength tunability, at the same time being electrically injected semiconductor lasers offering development of compact systems. Thus, they can serve high-end and upcoming applications. Prominent examples are monitoring and sensing in industrial process control, bio-sensing. There is a growing interest in application of QCLs to free-space optical transmission systems, potentially leading to optical links of higher resilience to weather conditions. A well-established field of research of photonics integrated circuits is also looking into possibility of employing mid-infrared lasers and solutions to demonstrate mid-IR PIC systems. The progress that photonic integration is currently undergoing may be compared to that of electronic integration nearly half a century ago. Its development will not only enable the transmission of huge amounts of information - particularly in optical data communication – but will also pave the way for large scale fabrication, the minimization of assembly processes, and the reduction in energy consumption. The purpose of the mid-IR PIC component integration technology is to enable the integration of individual components of the PIC system - in particular the Quantum Cascade Lasers with passive structures integrated on PIC.In this work, we will provide a brief overview of QCL technology and design issues as well as discuss selected developments of the recent research conducted in Łukasiewicz- IMIF, among them the coupled cavity and taper device geometries, as well as the progress of development of mid-IR photonic integrated circuits platform.

In this paper, we present the methodology for precise calibration of the Molecular Beam Epitaxy (MBE) growth process and achieving run-to-run stability of growth parameters. We present the analysis of the influence of fluxes stability during the growth of long wavelength quantum cascade laser structures designed for the range λ ~ 12–16 µm on wavelength accuracy with respect to desired emission wavelength. The active region of the lasers has a complex structure of nanometer thickness InxGa1−xAs/InyAl1−yAs superlattice. As a consequence, the compositional and thickness control of the structure via bulk growth parameters is rather difficult. To deal with this problem, we employ a methodology based on double-superlattice test structures that precede the growth of the actual structures. The test structures are analyzed by High Resolution X-ray Diffraction, which allows calibration of the growth of the complex active region of quantum cascade laser structures. We also theoretically studied the effect of individual flux changes on the emission wavelength and gain parameters of the laser. The results of simulations allow for the determination of flux stability tolerance, preserving acceptable parameters of the laser and providing means of emission wavelength control. The proposed methodology was verified by the growth of laser structures for emission at around 13.5 μm.

Quantum-cascade (QC) vertical-cavity surface-emitting lasers (VCSELs) could combine the single longitudinal mode operation, low threshold currents, circular output beam, and on-wafer testing associated with VCSEL configuration and the unprecedented flexibility of QCs in terms of wavelength emission tuning in the infrared spectral range. The key component of QC VCSEL is the monolithic high-contrast grating (MHCG) inducing light polarization, which is required for stimulated emission in unipolar quantum wells. In this paper, we demonstrate a numerical model of the threshold operation of a QC VCSEL under the pulse regime. We discuss the physical phenomena that determine the architecture of QC VCSELs. We also explore mechanisms that influence QC VCSEL operation, with particular emphasis on voltage-driven gain cumulation as the primary mechanism limiting QC VCSEL efficiency. By numerical simulations, we perform a thorough analysis of the threshold operation of QC VCSELs. We consider the influence of optical and electrical aperture dimensions and reveal the range of aperture values that enable single transversal mode operation as well as low threshold currents.

In 2022, we are celebrating the 50th anniversary of the "Jaszowiec" International School & Conference on the Physics of Semiconductors. One of the highlights of this anniversary was the reminiscence session at the Jaszowiec 2022 meeting, recalling the most important achievements in the field of semiconductor physics and technology in the institutions organising the Conference. This paper aims to highlight the accomplishments of the Institute of Electron Technology, Warsaw, with particular emphasis on II-VI and III-V compounds and their application in electronic and optoelectronic devices. Specifically, the review covers narrow-gap HgCdTe for galvanomagnetic devices, GaAs-, GaP-, InP-, and GaSb-based materials for optoelectronics and photonics, SiC and GaN for radio-frequency and high-power electronics, and finally ZnO and InGaZnO for transparent electronics and sensors. Research results on device physics, material development, device design, and processing are presented.

Nonequilibrium Green's function modeling of the structure used for III-V quantum cascade lasers emitting at approximately 5-mu m wavelength is performed to get insight into and analyze the processes that determine the linewidth of the optical (inter-sub-band) transition. Theoretical results are compared with electroluminescence data collected for real structures. Excellent agreement is found for both the transition energy of approximately 234 meV and the linewidth of approximately 32 meV, typical for this sort of device. Careful inspection of simulation data shows that, for these structures, the interface-roughness (IR) scattering contributes to the optical linewidth congruent to 50%. The decreased broadening due to IR scattering is not due to very smooth interfaces, but rather due to the finite carrier concentration and the decreased population of final states k' available for the initial state k in the limit of vanishing in-plane momentum k -> 0. Further line narrowing is caused by nonparabolicity coupled with the highly nonthermal occupation of the lower laser sub-band, which destroys the population inversion for the hot carriers.

We report on experimental characterization of butt-coupling between a quantum cascade laser operating around the wavelength of 4.5 mu m and a silica hollow core anti-resonant fiber. The used fiber has a single ring of non-touching capillaries surrounding a 42.5 mu m dimeter air core and a mid-infrared transmission window in the wavelength range of 2.8 to 4.7 mu m. A lens-less butt-coupling interconnection is established and coupling efficiency of 22% is achieved with over 100 mW of power at the fiber output. Bending losses in this test-bed system are verified depending on radius with the loss remaining below 1 dB/m for 20 mm loops, while bend losses exceeding 10 dB/m are observed when the fiber is bent down to a 5-mm radius. The presented coupling dramatically improves the output beam quality of the quantum cascade laser with a measured NA = 0.45. The beam at the fiber output has a circular shape, measured M-2 = 1.04 and uniform numerical aperture of NA = 0.13. Together with the hollow core fiber geometry, the proposed system would be suitable for simple implementations of absorption spectroscopy of popular atmospheric agents, like N2O.

In this work, two-section, coupled cavity, mid-IR quantum cascade lasers (QCLs) were characterized in terms of their tuning range and emission stability under operation towards potential application in detection systems. Devices were processed by inductively coupled plasma reactive ion etching (ICP-RIE) from InP-based heterostructure, designed for emission in the 9.x micrometer range. Single mode devices were demonstrated with a better than 20 dB side mode suppression ratio (SMRS). The fabrication method resulted in improved yield, as well as high repeatability of individual devices. Continuous, mode-hop-free tuning of emission wavelength was observed across ~4.5 cm−1 for the range of temperatures of the heat sink from 15 °C to 70 °C. Using the thermal perturbation in the lasing cavity, in conjunction with controlled hopping between coupled-cavity (CC) modes, we were able to accomplish tuning over the range of up to ~20 cm−1.

We investigate molecular beam epitaxy (MBE) growth conditions of micrometers-thick In0.52Al0.48As designed for waveguide of InGaAs/InAlAs/InP quantum cascade lasers. The effects of growth temperature and V/III ratio on the surface morphology and defect structure were studied. The growth conditions which were developed for the growth of cascaded In0.53Ga0.47As/In0.52Al0.48As active region, e.g., growth temperature of Tg = 520 °C and V/III ratio of 12, turned out to be not optimum for the growth of thick In0.52Al0.48As waveguide layers. It has been observed that, after exceeding ~1 µm thickness, the quality of In0.52Al0.48As layers deteriorates. The in-situ optical reflectometry showed increasing surface roughness caused by defect forming, which was further confirmed by high resolution X-ray reciprocal space mapping, optical microscopy and atomic force microscopy. The presented optimization of growth conditions of In0.52Al0.48As waveguide layer led to the growth of defect free material, with good optical quality. This has been achieved by decreasing the growth temperature to Tg = 480 °C with appropriate increasing V/III ratio. At the same time, the growth conditions of the cascade active region of the laser were left unchanged. The lasers grown using new recipes have shown lower threshold currents and improved slope efficiency. We relate this performance improvement to reduction of the electron scattering on the interface roughness and decreased waveguide absorption losses.

In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InPQCLs taper quantum cascade lasers are presented. In order to increase output power while keeping good beam quality, taper design of resonator was used. We have studied devices emitting at 4.5 mu m with different shapes (linear, concave and convex) and angles of taper waveguide section, to optimize the output beam parameters, namely M-2 and brightness. Experimental results demonstrate that convex geometry taper laser with 1.7 degrees taper shows the best performance, the highest output power up to 5 W and the smallest horizontal beam divergence of 5.6 degrees in the fundamental mode. This design is also characterized by the highest brightness.

The paper focuses on the design, fabrication and characterization of monolithic, coupled cavity two-section quantum cascade lasers. The devices were fabricated by reactive ion etching from InP-based heterostructure designed for emission in 9.x micrometer range. To make the device attractive for sensing applications, the idea of the coupled-cavity device was employed, giving the possibility of single longitudinal mode operation. We have previously presented devices fabricated by means of focused ion beam post-processing. However, FIB etching is challenging and time-consuming. In order to overcome the relatively low throughput of the FIB process, in this work, gaps separating sections were defined by dry etching during the fabrication process. Careful optimization of the dry etching process resulted in very good control of gap geometry. Quality of mirrors formed by RIE did not introduce high scattering loss into the cavity, as the threshold current density was not increased significantly. Devices routinely exhibited side mode suppression ratio of more than 20 dB. Approach to fabricate two-section devices by dry etching resulted in improved yield as well as high repeatability of the performance of individual devices. Monolithic, electrically isolated, two-section devices were also fabricated and characterized. We will present a comparison of the performance of different designs and discuss their characteristics, fabrication challenges and stability against operating conditions.

In this paper external degradation type of failure of Quantum Cascade Laser is analyzed. The failure mode discussed in the work is connected with the damage of the gold, top electrode. We show how fabrication faults translate to degradation of device and monitor temperature distributions as well as electrical characteristics of the device during the process. The aim of this research is to demonstrate how external degradation process develops in case of AlInAs/InGaAs/InP quantum cascade lasers.

In the work we have considered the influence of various parameters and phenomena on the absorption edge of InAs/GaSb superlattices. Calculations have been performed with the use of the 8-band k⋅p method. Results of the analysis have allowed us to form an opinion how big is the impact of temperature, band offset energy, strain and different types of interfaces on the absorption edge of the investigated structures. Such comparison hasn't been done, yet, especially since our outcomes relate not only to the selected, individual superlattices, but present the issue more comprehensively, regarding two series of periodic structures, derived from the (InAs)8ML/(GaSb)8ML one. Conclusions, which come from this work are useful particularly in terms of difficulties in adopting proper values of the material parameters for the numerical model of InAs/GaSb superlattice. Results presented in this article will be helpful while designing the more sophisticated periodic structures based on InAs/GaSb material system.

Nonequilibrium Green’s function method is used to calculate electronic and optical characteristics of various quantum cascade structures emitting light at ~ 5.2 μm wavelength. Basing on these simulations, the choice of optimal design can be done.

We report recent results of works on quantum cascade lasers at the Institute of Electron Technology. During that time we have developed technology of lasers emitting at wavelengths 9.0–9.5 μm and 4.7 μm, based on InGaAs/AlGaAs/GaAs and InAlAs/InGaAs/InP heterostructures; both lattice matched and strain compensated. The structures were grown by molecular beam epitaxy MBE and by metalorganic vapor phase epitaxy MOVPE. The InGaAs/AlGaAs/GaAs lasers were grown by MBE. For InP based lasers three types of structures were investigated; the one grown exclusively by MBE without MOVPE overgrowth, the second fabricated by hybrid approach combining MBE grown AlInAs/InGaAs active region with MOVPE grown InP top waveguide layer and the third one with both the top and the bottom InP waveguide grown by MOVPE. Regardless of the waveguide construction, the active region was grown by MBE in every case. The lasers were fabricated in double trench geometry using standard processing technology. The buried heterostructure lasers were also investigated.

The paper describes the status of technology of mid-IR quantum cascade lasers (QCLs) based on GaAs/AlGaAs and InAlAs/InGaAs/InP material system developed at the Institute of Electron Technology. Two main types of lasers were investigated. First, was based on lattice matched active region designed for wavelengths of lambda=9.0 mu m-10.0 mu m. The second, was based on strain-compensated active region designed for wavelengths of lambda=4.5 mu m-5.5 mu m. Basic characteristics and parameters of all types of lasers are discussed. Possible applications in which the lasers developed at ITE can compete with those available on world market are indicated.

Tuning the wavelength of emitted radiation is a tremendous feature of quantum cascade lasers which enables their use in various applications. Usually, this tuning is executed by the change of the bias current or the temperature. In this paper, it is demonstrated, both experimentally and theoretically, that yet another possibility of tuning laser wavelength offers the change of doping density. For the experimental demonstration, a set of GaAs/AlGaAs devices emitting in the range 9.3–9.7 µ\({\rm {m}}\) was MBE grown and processed. For the theoretical analysis, the simulations that employ nonequilibrium Green’s function formalism, applied to the single-band effective mass Hamiltonian, are used. The analysis shows that the physical mechanism responsible for wavelength-doping correlation is a linear Stark effect. The range of tuning is limited on both low and high doping side. Both these limits are established and discussed.

The aim of the work is to discuss possibility of application of Quantum Cascade Lasers in practical realization of laser based free space communication system. Additionally, some aspects of development of technology of QC lasers will be indicated with respect to FSO systems.

Flash-based SSDs are usually equipped with an onboard cache to further improve system performance by smoothing the gap between the upper-level applications and lower-level flash chips. Since modern SSDs are usually composed of multiple flash chips, and the load of flash chips are significantly different, it is very meaningful to be aware of the chip load condition when designing a cache replacement algorithm. Nevertheless, existing cache replacement algorithms only consider to reduce the cache miss ratio so as to reduce the I/O requests to the underlying flash memory as much as possible, none of them considers the load condition of flash chips. In this paper, we propose a Load-aware Cache Replacement algorithm, called LCR, to improve the performance of flash-based SSDs. The basic idea is to give a higher priority to cache the blocks on overloaded flash chips. We evaluate the performance of our scheme by using a trace-driven simulator with multiple real-world workloads, and results show that compared with the most common algorithm LRU and the state-of-the-art algorithm GCaR, LCR reduces the average response time by as much as 39.2% and 12.3%, respectively.