For a GaAs/AlGaAs terahertz (THz) quantum cascade laser (QCL) with a double metal waveguide (DMWG) based on Au and Cu metal plates and Ti and Ta adhesion layers, the dumping parameters and THz mode loss spectra were calculated. It has been shown that to minimize losses in high-temperature DMWG QCL designs, it is advisable to use Ti less than 5 nm thick or Ta less than 10 nm thick as adhesion layers for Au. The use of the proposed waveguide with a thickness of 20 mu m will lead to the creation of a room temperature THz QCL. (c) 2024 Optica Publishing Group

We report on the implementation of a terahertz two-photon quantum cascade laser operating in a continuous wave mode. Lasers that can emit two photons as a result of the relaxation of a single electron between two states of the same parity have been discussed since the early days of the laser era, but implementation has been hampered by the lack of a suitable gain medium. The semiconductor structure of a quantum cascade laser seems to be an ideal medium for realizing such two-photon emission. Our work demonstrates dual-band laser radiation in the range of 3.1-3.9 THz (104-130 cm(-1)) at temperatures up to 90 K.

A band design of a quantum cascade laser with a generation frequency higher than 6 THz and an active region based on four GaAs/Al0.14Ga0.86As quantum wells is proposed. Calculations were carried out based on the solution of the Schrödinger equation taking into account the dephasing of quantum states, as well as a closed system of balance equations. The temperature dependences of the gain at frequencies of 6.3–6.6 THz were calculated for the proposed quantum cascade laser with a double metal waveguide. Features of the proposed laser structure include two injection quantum wells and the suppression of non-radiative transitions between laser levels. According to calculations, this provides the maximum operating temperature of up to 81 K at 6.4 THz. The results of this study open up the way for quantum cascade lasers based on GaAs/AlGaAs to operate at frequencies above 6 THz.

We have demonstrated a quantum cascade laser (QCL) with a generation frequency of about 3.8 THz, grown by metal-organic vapor phase epitaxy. The multilayer heterostructure for QCLs consists of 185 repetitions of an active module containing four GaAs/Al0.15Ga0.85As quantum wells. The threshold current and threshold voltage of the fabricated QCL were 2.25 kA/cm2 and 19.7 V, respectively. The QCL oscillations were carried out in the multimode regime, and the detection of terahertz radiation continued with an increase in the laser temperature up to 60 K.

We study the band designs of terahertz quantum–cascade lasers (THz QCLs) with an active region of GaAs/Al x Ga 1− x As quantum wells (QWs) by using the solution of the Schrödinger equation with allowance for dephasing of quantum states, as well as solving a system of closed balance equations. For two-QW designs with increased Al x Ga 1− x As potential barrier height ( x = 0.20, 0.25, and 0.30), temperature dependences of the peak gain are calculated. It is shown that by increasing the aluminum content in the barrier layers compared to the conventional x = 0.15, it becomes possible to increase the operating temperatures of THz QCLs by more than 220 K. Two new designs of laser transitions are proposed to increase the output power and operating temperature of THz QCLs. To increase the output power, a design with a two-photon scheme of laser transitions was proposed, which causes an approximately twofold slower drop in the nonlinear gain with increasing photon density. To increase operating temperatures, it is suggested to use weakly localized electron states with wave functions extending over two or more periods of the structure. The matrix element of dipole transitions in such structures is shown to be greatly increased, while the lower laser level has a larger energy gap with the injector, is less populated, and is more temperature stable compared to the conventional designs. In this case, the calculated value of the maximum operating temperature is about 250 K.

The design of a terahertz (THz) quantum cascade laser (QCL) with an active module based on three GaAs/Al0.18Ga0.82As quantum wells for high-temperature generation at a frequency of about 3.3 THz is optimized. A heterostructure based on the developed design with an active region thickness of 10 μm is grown by molecular-beam epitaxy with a deviation of the active-module thickness from the nominal of less than 1%. The fabricated THz QCLs with a double metal waveguide demonstrate lasing up to a temperature of 125 K. Investigations of the I–V characteristics, the dependences of the integrated emission on the current, and the lasing spectra show good agreement with the calculated characteristics.

In this work, we conduct research of spectral and power characteristics of quantum cascade lasers (QCLs) based on a GaAs/Al0.15Ga0.85As active region emitting at 2.3 (A), 3.2 (B) and 4.1 (C) THz. The QCL devices had a double-metal Au waveguide and operated in pulsed mode with 1.5–9 us pulses at 20 Hz repetition rate. Using the integral output power curves measured with different pulse durations, we consider the potential mechanisms of QCL temperature degradation using Arrhenius plots. Moreover, we present the spectra of the lasers measured at fixed operating points for devices A, С and with current scanning for device B in a wide temperature range from 5 to 120 K. We hope that our results will prove useful for research concerning QCL maximum operating temperatures.

We propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. A model for accounting for hot phonons is developed for calculating the nonequilibrium temperature of electrons and holes. Using a comprehensive model accounting for carrier drift and diffusion, Auger recombination, and hot-phonon effects, we predict of lasing at λ∼3 μm at room temperature in the 2.1 nm HgTe/Cd0.85Hg0.15Te quantum well heterostructure. The output power in the pulse can reach up to 600 mW for 100 nanosecond-duration pulses.

Objectives. Terahertz quantum-cascade lasers (THz QCLs) are compact solid-state lasers pumped by electrical injection to generate radiation in the range from 1.2 to 5.4 THz. The THz QCL operating frequency band contains absorption lines for a number of substances that are suitable for biomedical and environmental applications. In order to reduce the size and cost of THz QCLs and simplify the use of THz sources in these applications, it is necessary to increase the operating temperature of lasers.Methods. To calculate electron transport in THz QCLs, we used a system of balance equations based on wave functions with reduced dipole moments of tunnel-bound states.Results. As a result of the calculations, an original band design with a period based on three GaAs/Al0.18Ga0.82As quantum wells (QWs) and a gain maximum at about 3.3 THz was proposed. Based on the developed design, a THz QCL was fabricated, including the growth of a laser structure by molecular beam epitaxy, postgrowth processing to form strip lasers with a double metal waveguide, as well as an assembly of lasers mounted on a heat sink. The developed THz QCLs was capable of lasing at temperatures of up to 125 K as predicted by the performed calculations. We also studied band designs based on two GaAs/AlxGa1–xAs QWs having varying aluminum contents in the barrier layers (x = 0.20, 0.25, and 0.30).Conclusions. The calculated temperature dependences of the peak gain for two-QW designs with x > 0.2 confirm the possibility of creating THz QCLs operating at temperatures above 200 K. Thus, we have proposed two-QW band designs that outperform existing high-temperature designs in terms of maximum operating temperature.

We have demonstrated a quantum cascade laser (QCL) with a generation frequency of about 3.8 THz, grown by metal-organic vapor phase epitaxy. The multilayer heterostructure for QCLs consists of 185 repetitions of an active module containing four GaAs/Al0.15Ga0.85As quantum wells. The threshold current and threshold voltage of the fabricated QCL were 2.25 kA/cm2 and 19.7 V, respectively. The QCL was generated in the multimode regime, and the detection of terahertz radiation continued with an increase in the laser temperature up to 60 K.

HgCdTe is promising as a material to solve a problem of the development of semiconductor sources with an operational frequency range of 6-10 THz due to the small optical phonon energies and electron effective mass. In this study, we calculate the dependence of the metal-metal waveguide characteristics on the number of cascades for the 3-well design HgCdTe-based quantum cascade laser at 8.3 THz. It is shown that four cascades are sufficient for lasing at a lattice temperature of 80 K due to the large gain in the active medium. The results of this study provide a way to simplify the fabrication of thin active region HgCdTe-based quantum cascade lasers for operation in the range of the GaAs phonon Reststrahlen band inaccessible to existing quantum cascade lasers.

In this work, we conduct research of spectral and power characteristics of quantum cascade lasers (QCLs) based on a GaAs/Al0.15Ga0.85As active region emitting at 2.3 (A), 3.2 (B) and 4.1 (C) THz. The QCL devices had a double-metal Au waveguide and operated in pulsed mode with 1.5–9 μs pulses at 20 Hz repetition rate. Using the integral output power curves measured with different pulse durations, we consider the potential mechanisms of QCL temperature degradation using Arrhenius plots. Moreover, we present the spectra of the lasers measured at fixed operating points for devices A, C and with current scanning for device B in a wide temperature range from 5 to 120 K. We hope that our results will prove useful for research concerning QCL maximum operating temperatures.

The effect of gain saturation in quantum-cascade structures with 2–4 quantum wells per period is herein analyzed on the basis of a system of balance equations. It is shown that the nonlinearity parameter decreases with an increase in the relaxation rate of laser levels, but the total current through the structure also increases. The use of the proposed multiphoton designs leads to a decrease in the non-linearity parameter without increasing the operating current. For example, in a two-photon scheme of laser transitions with the same transition probabilities and differential gains, two times slower saturation of the gain with an increase in the photon density is achieved, which leads to a high generation efficiency than in single-photon schemes.

A new lasing scheme with sequential two-photon emission in the gain module for terahertz quantum cascade laser (THz QCL) is proposed and experimentally demonstrated. THz QCLs based on MBE- and MOCVD-grown structures with two-photon design have a lasing frequency of 3.8 THz and maximum operation temperature around 100 K.

In this work, we have optimized the THz QCL design with an active module based on three GaAs/Al0.18Ga0.82As quantum wells for high-temperature generation at a frequency of about 3.3 THz. A heterostructure based on the developed design with an active region thickness of 10 μm was grown by molecular beam epitaxy with a deviation of the active module thickness from the nominal less than 1%. The fabricated THz QCLs with a double metal waveguide demonstrate lasing up to a temperature of 125 K. Investigations of the I–V characteristics, the dependences of the integrated radiation on the current and the lasing spectra showed good agreement with the calculated characteristics.

The efficiency of electric pumping of THz quantum-cascade lasers (QCLs) with strip geometry is studied depending on the number and position of contact pads. The numerical simulation of the electric potential distribution in the THz QCL active region is used to determine the required thicknesses of the upper metallisation layers of the THz QCLs to minimize the voltage drop along the laser structure in the case of nonuniform current supply. It is found that the efficiency of electric pumping in the case of a centrally located contact is significantly higher than when the contact pads are located near the laser structure edges. From the calculated dependence of the THz QCL integral power on the thickness of the upper metal layer, it is shown that for effective current injection, the contact pads must be located at a distance of less than 0.5 mm from each other.

We have designed and fabricated 2.3 THz QCL with active module based on 4 QWs GaAs/Al0.15Ga0.85As. The light-current-voltage (L-I-V) characteristics and emission spectra of fabricated THz QCL are investigated. The nonmonotonic behavior of L–I characteristic and a large number of discontinuities in I-V characteristic is observed. Our calculations show that such electric instabilities are associated with the field inhomogeneity across the active region (electric field domains). We investigate transmission spectra of incident radiation of GaAs and AlGaAs/GaAs structures with two highly absorption optical response regions. Thus, to improve the performance and extend the operation frequencies of THz QCLs it is needed to develop new concepts of active region designs for avoiding the formation of electric field domains and employ novel material systems for lasing in the frequency range 8-11 THz.