Short Barriers for Lowering Current-Density in Terahertz Quantum Cascade Lasers

Abstract

Scattering due to interface-roughness (IR) and longitudinal-optical (LO) phonons are primary transport mechanisms in terahertz quantum-cascade lasers (QCLs). By choosing GaAs/Al0.10Ga0.90As heterostructures with short-barriers, the effect of IR scattering is mitigated, leading to low operating current-densities. A series of resonant-phonon terahertz QCLs developed over time, achieving some of the lowest threshold and peak current-densities among published terahertz QCLs with maximum operating temperatures above 100 K. The best result is obtained for a three-well 3.1 THz QCL with threshold and peak current-densities of 134 A/cm2 and 208 A/cm2 respectively at 53 K, and a maximum lasing temperature of 135 K. Another three-well QCL designed for broadband bidirectional operation achieved lasing in a combined frequency range of 3.1–3.7 THz operating under both positive and negative polarities, with an operating current-density range of 167–322 A/cm2 at 53 K and maximum lasing temperature of 141 K or 121 K depending on the polarity of the applied bias. By showing results from QCLs developed over a period of time, here we show conclusively that short-barrier terahertz QCLs are effective in achieving low current-density operation at the cost of a reduction in peak temperature performance.

Dynamic modulation and impedance characteristics of a terahertz quantum cascade laser

“…T = 50 K is the operating temperature of the device. 32 Figure 4 shows the impedance response as a function of frequency for different bias currents with the device parameters listed in Table I. At a given current, the device impedance is fairly flat when the frequency is below 1 GHz; as the frequency increases, the impedance exhibits a resonance at a particular frequency.…”

“…By assuming that all quantum wells are identical and the confinement factors are the same for all gain stages, a simplified three-level rate equation model is applied to analyze the dynamic properties of THz QCLs. The QCL device considered for this paper is based on the resonant-tunneling injection and resonant-phonon depopulation scheme; 32 however, the theoretical model can still be applied to other QCL designs, such as a chirped superlattice, 2 and bound to continuum. 33 The waveguide for the considered THz QCL is a metal-metal waveguide.…”

“…Simulated and measured32 output power per facet and the electron density in level 3 and level 2 as a function of bias currents. There is a discontinuity in the increase in the electron density in level 3 and level 2 at a threshold current of 0.51 A.…”

Keen Investigation of the Electromagnetic Scattering Characteristics of Tiltrotor Aircraft Based on Dynamic Calculation Method

“…The multi-rotor dynamic scattering method is presented to evaluate the RCS of the compound helicopter, which guides the calculation of the radar characteristics of the tilt-rotor aircraft [18][19][20]. It can be seen that the radar stealth characteristics of fixed-wing aircraft and helicopters [21][22][23][24] and the aerodynamics and control strategies of tilt-rotor aircraft have received rich research results [25][26][27][28][29], while there is very little work and investigation in the stealth research of tiltrotor aircraft. The exploration of tilt-rotor RCS has academic significance and engineering value for the survivability and comprehensive combat effectiveness of this aircraft on the future battlefield.…”

In-situ thin film copper–copper thermocompression bonding for quantum cascade lasers

“…Moreover, development of pulsed devices enabled the lasers to provide wavelength up to 16.0 lm [18]. However, cryogenic cooling is still required for longer wavelengths [19] and the maximum operating temperatures appeared to be in the range of 175-210 K for 3.0 THz emissions [20,21].…”