Multidimensional Conduction-Band Engineering for Maximizing the Continuous-Wave (CW) Wallplug Efficiencies of Mid-Infrared Quantum Cascade Lasers

Quantum Cascade Lasers: Electrothermal Simulation

“…While good output powers and WPEs have been achieved, long-term reliability of these devices under RT CW operation remains a critical problem [5,6]. These devices are prone to catastrophic breakdown owing to reasons that are not entirely understood, but are likely related to thermal stress that stems from prolonged highpower operation [5].…”

“…In addition to improved device lifetime, we seek better CW temperature performance (higher characteristic temperatures T 0 and T 1 , defined below) [6]. The first aspect is a weaker temperature dependence of the threshold current density.…”

“…Furthermore, these QCLs must also have high wall-plug efficiency (WPE, the ratio of emitted optical power to the electrical power pumped in) and long-term reliability under these high-stress operating conditions. As the stress likely stems from excessive nonuniform heating while lasing [5,6], improving device reliability and lifetime goes hand-in-hand with improving the WPE. * iknezevic@wisc.edu…”

Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers

“…While good operating powers and WPEs have been achieved in devices close to 5 µm wavelengths, long-term reliable RT CW operation at high powers (in excess of a few hundred mW) remains a challenge due to high thermal stress [13,14] that is worst in short-wavelength devices that have high strain and high thermal impedance mismatch between layers [10,11,15,16]. In addition to improved device longevity, what is needed is better CW temperature performance, with weaker temperature dependencies of the threshold current density J th ∼ exp (T/T 0 ), with T 0 being the characteristic temperature, and of the differential quantum efficiency η ∼ exp (−T/T 1 ), also known as the slope efficiency, with a characteristic temperature T 1 [14].…”

“…In addition to improved device longevity, what is needed is better CW temperature performance, with weaker temperature dependencies of the threshold current density J th ∼ exp (T/T 0 ), with T 0 being the characteristic temperature, and of the differential quantum efficiency η ∼ exp (−T/T 1 ), also known as the slope efficiency, with a characteristic temperature T 1 [14]. Recently, deep-well structures with tapered-barrier active regions have demonstrated significant improvements in the T 0 and T 1 values with respect to those in the conventional 4.6 µm device [8], underscoring that suppression of leakage paths plays a key role in temperature performance [4,14,17]. However, the microscopic mechanisms and leakage pathways that contribute to these empirical performance parameters remain unclear.…”