Abstract
In order to realize high temperature lasing of low frequency (< 2 THz) terahertz quantum cascade lasers (THz QCLs), selective carrier injection into an upper lasing level using an indirect injection (II) scheme is an effective method for inducing population inversion. The II scheme is realized with a four-level system. However, a three-level system that operates at low applied bias voltages causes additional lasing at higher frequencies (4～5 THz). By detuning the wave functions at the three lasing levels operating at low bias voltages, we were able to operate an II scheme THz QCL at a single stable frequency. Utilizing the higher injection selectivity, achieved through an indirect scattering-assisted injection process combined with diagonal emission, we were able to demonstrate stable operation of an AlGaAs/GaAs QCL operating at 1.89 THz at temperatures up to 160 K.
Highlights
The terahertz (THz) region in the electromagnetic spectrum has drawn much attention due to the wide range of applications available to this region, such as those in spectroscopy, imaging, remote sensing, and communications
This work demonstrate an Al0.175Ga0.825As/GaAs Quantum cascade lasers (QCLs) design that uses a combination of II and diagonal emission in the THz region
Structures were grown by solid-source molecular beam epitaxy (MBE); A 3.95 / 7.99 / 2.16 / 9.02 / 3.19 / 6.86 / 3.76 / 14.38 structure and 2.1×1016 cm-3 modulation doping of the widest well (14.38 nm) were employed
Summary
The terahertz (THz) region in the electromagnetic spectrum has drawn much attention due to the wide range of applications available to this region, such as those in spectroscopy, imaging, remote sensing, and communications. Quantum cascade lasers (QCLs) [2] are compact semiconductor light sources that utilize carrier recycling and intersubband transitions in repeated quantum well (QW) structures, and they have been demonstrated to operate successfully in the mid-infrared (mid-IR) [2] and THz [3] regions. They are arguably the only THz solid-state sources with average optical output power levels much greater than one milliwatt (mW) at pulse mode [4] and sub mW at CW operation [5]. In contrast to the room temperature operation of mid-IR
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