Evaluation of Material Systems for THz Quantum Cascade Laser Active Regions

Abstract

Quantum cascade lasers (QCLs) have been realized in several different material systems. In the mid-infrared, active regions are predominantly based on In 0.53 Ga 0.47 As and InAs as quantum well material. Market-ready devices routinely provide continuous-wave operation at room temperature. For their THz counterparts, the situation is less clear. The most common material system for THz QCLs is the inherently lattice-matched combination of GaAs with Al 0.15 Ga 0.85 As barriers. Yet, these devices still only reach a maximum operating temperature of 200 K with a lack of progress within the past years. Based on the identification of key parameters, this work reviews material systems for quantum cascade lasers with an emphasis on material and growth-related aspects and the goal to identify promising candidates for future device generations. Similar active regions realized in different material systems allow to estimate the gain per unit thickness, as well as total growth times and relative thickness errors.

Sensing and imaging using laser feedback interferometry with quantum cascade lasers

“…1,29 Figure 1(c) shows scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of an MIR QCL, in which the periodic nature of the growth can be clearly seen. To date, best performance has been obtained with four semiconductor material systems: 156 GaInAs/ AlInAs grown on InP substrates; GaAs/AlGaAs grown on GaAs substrates; AlSb/InAs grown on InAs substrates; and InGaAs/AlInAsSb, InGaAs/GaAsSb, or InGaAs/AlInGaAs grown on InP substrates. The choice of the material system affects the intersubband gain, the shortest possible wavelength of operation dictated by the conduction band, and the location of the Reststrahlen bands.…”

“…The choice of the material system affects the intersubband gain, the shortest possible wavelength of operation dictated by the conduction band, and the location of the Reststrahlen bands. 3,155,156 The intrinsic (quantum noise limited) linewidth of QCLs is subkilohertz, around 500 Hz for MIR QCLs and around 100 Hz for THz QCLs. [30][31][32][33][34] Practical instantaneous linewidths are around 10 kHz, and on the order of tens of megahertz over longer time-scales.…”

Barrier Height Tuning of Terahertz Quantum Cascade Lasers for High-Temperature Operation

“…Designs with improved LO-phonon-assisted depopulation process via a double extraction mechanism or a double-phonon resonant depopulation have been realized. Heterostructures with higher barriers for reduced carrier leakage were studied. , Alternative material systems to GaAs/AlGaAs, with lower effective electron mass, are promising because the optical gain in the heterostructure scales inversely to the effective mass. , Such materials include InGaAs/InAlAs, , InGaAs/AlGaInAs, − InGaAs/GaAsSb, and InAs/AlAsSb with material compositions lattice matched to InP and InAs, respectively. The first three material systems suffer from very thin barriers and interface roughness effects but show already good results with maximum operation temperatures of 155 K and output powers up to 600 mW in pulsed operation .…”

Prospects of temperature performance enhancement through higher resonant phonon transition designs in GaAs-based terahertz quantum-cascade lasers

“…A variety of materials and approaches are employed in order to improve the performance of QCLs [7,25], and this must be underpinned by a good understanding of carrier transport within these devices. The dominant material system for THz QCLs is GaAs/AlGaAs due to its performance and technology level, however great interest is drawn by semiconductors with lower effective masses as InGaAs and InAs [26,27] or higher longitudinal optical (LO) phonon energy such as GaSb and GaN [25,28] and reliable and efficient modelling approaches are needed for further development of THz technology.…”