Indirectly pumped 37 THz InGaAs/InAlAs quantum-cascade lasers grown by metal-organic vapor-phase epitaxy

Abstract

Device-performances of 3.7 THz indirect-pumping quantum-cascade lasers are demonstrated in an InGaAs/InAlAs material system grown by metal-organic vapor-phase epitaxy. The lasers show a low threshold-current-density of ~420 A/cm2 and a peak output power of ~8 mW at 7 K, no sign of parasitic currents with recourse to well-designed coupled-well injectors in the indirect pump scheme, and a maximum operating temperature of Tmax ~100 K. The observed roll-over of output intensities in current ranges below maximum currents and limitation of Tmax are discussed with a model for electron-gas heating in injectors. Possible ways toward elevation of Tmax are suggested.

Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage

“…At a temperature of 10 K, the threshold current density (J th ) was 1.29 kA/cm 2 , the peak output power was 4.8 mW at a current density of 1.60 kA/cm 2 , and the slope efficiency was 14 mW/A. The peak power is comparable with other indirect injection designs [20][21][22], but the current is much higher, resulting in significant Joule heating within the device. A regression of the temperature evolution of the threshold current density to the empirical equation J th = J 0 + J 1 exp(T/T 0 ) yields the value T 0 = 27 K. The small T 0 indicates large thermally activated current, resulting in a large threshold current density of 1.58 kA/cm 2 at 123 K. The emission spectra measured at a range of biases are shown in Fig.…”

“…8. At low temperature (10 K), LO phonon scattering between the laser levels is weak and an increase in f 21 only results in a small decrease in ∆n 21 . The gain therefore increases from 22.1 cm −1 to 43.6 cm −1 as f 21 varies from 0.32 to 0.82.…”

“…One solution to improve the performance at higher temperatures is to suppress phonon scattering between the laser levels by using designs based on a diagonal Table 1. radiative transition [11,15,16]. Alternatively, an indirect injection scheme [17][18][19][20][21][22] can be used, in which LO-phonon scattering replaces resonant tunneling for carrier injection; QCL devices based on this indirect injection scheme have operated up to 163 K at 1.8 THz [19]. A simple 'extraction-controlled' design has also been proposed [23], in which only one phonon scattering process is employed to realize both carrier extraction and injection simultaneously; this contrasts with the two LO-phonon scattering processes used for separate carrier extraction and injection in previous indirect injection schemes.…”

Design for Stable Lasing of an Indirect Injection THz Quantum Cascade Laser Operating at Less Than 2 THz

“…Even this design scheme still suffers difficulties in the THz region compared with mid-IR QCLs. After several theoretical proposals [10,11,12], and a few recent experimental reports [8,13,14,15,16], II designs show promising results and demonstrate that there is high potential for attaining lowfrequency, high-temperature THz QCLs. modulation doping of the widest well (14.38 nm) were employed.…”

High performance InGaAs/GaAsSb terahertz quantum cascade lasers operating up to 142 K

“…7 Consequently, this raises the question why THz QCLs are yet almost exclusively fabricated with GaAs/ AlGaAs and only a few attempts have been made using InGaAs/InAlAs. [8][9][10] Up to now, the maximum operating temperature of 122 K for InGaAs/InAlAs is considerably lower than for GaAs/AlGaAs. 5,9 Growth quality is one of the most restricting criteria when it comes to the realization of QCL active regions in any material system.…”