Thermal analysis of short wavelength InGaAs/InAlAs quantum cascade lasers

Quantum Cascade Lasers: Electrothermal Simulation

“…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]. This kind of thermal stress is worst in short-wave length devices that have high strain and high thermal impedance mismatch between layers [11,12,16,17].…”

“…Thermal transport in QCLs is often described through the heat diffusion equation, which requires accurate thermal conductivity in each region, a challenging task for the active core that contains many interfaces [17,[45][46][47][48]. It is also very important to include nonequilibrium effects, such as the nonuniform heat-generation rate stemming from the nonuniform temperature distribution [47] and the feedback that the nonequilibrium phonon population has on electron transport [26].…”

“…κ and κ ⊥ of a QCL Active Core Thermal transport inside the active core of a QCL is usually treated phenomenologically: κ is typically assumed to be 75% of the weighted average of the bulk thermal conductivities of the constituent materials, while κ ⊥ is treated as a fitting parameter (constant for all temperatures) to best fit the experimentally measured temperature profile [17,78]. We calculated the thermalconductivity tensor of a QCL active core [78] and showed that the typical assumption is not accurate and that the degree of anisotropy is temperature dependent (Fig.…”

“…Further, these layers are typically thick enough to be treated as bulk materials. Bulk-substrate (GaAs or InP) thermal conductivities are readily obtained for III-V materials from experiment, as well as from relatively simple theoretical models [17,48,78,80] (Table I). …”

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].…”