Investigations of carrier scattering into L‐valley in λ = 3.5 µm InGaAs/AlAs(Sb) quantum cascade lasers using high hydrostatic pressure

Abstract

In order to identify the performance limitations of InGaAs/ AlAs(Sb) quantum cascade lasers, experimental investigations of the temperature and pressure dependencies of the threshold current (I th ) were undertaken. Using the theoretical optical phonon current (I ph ) and carrier leakage (I leak ) to fit the measured threshold current at various pressures, we show that the electron scattering from the top lasing level to the upper L-minima gives rise to the increase in I th with pressure and temperature. It was found that this carrier leakage path accounts for approximately 3% of I th at RT and is negligible at 100 K.

Design considerations for λ ∼ 3.0- to 3.5-μm-emitting quantum cascade lasers on metamorphic buffer layers

“…1, with increasing strain, which means with increasing In content in the QWs, such leakage becomes a significant portion of the total roomtemperature J th value for devices grown on InP, unlike devices designed for emission in the 3.5-to 4.0-μm range. 15,42,43 Large Δ inj values, like the ones in Table 3, ensure that the backfilling-current density due to thermal excitation from the ground state in the injector region of a stage to the lower laser level in the AR of the previous stage is minimized. However, a trade-off exists here as too large a value for Δ inj will result in undesirably high voltages.…”

“…While relatively high T 0 values (152 to 166 K) were obtained, the T 1 value was moderately high (∼190 K) only for 3.56-μm-emitting devices, as it dropped to ∼116 K for 3.39-μm-emitting devices, most likely due to the onset of leakage to satellite valleys. 15 Similarly, 3.3-μm-emitting devices 16 have displayed low T 1 values (∼71 K), over the 250-to 300-K temperature range, indicating strong carrier leakage to satellite valleys. The T 0 values were also found to be low (100 K) above an operating temperature of 250 K, due to carrier leakage and possibly strong backfilling, considering the relatively high injector-doping level.…”

High-Power Mid-Infrared (λ∼3-6 μm) Quantum Cascade Lasers

“…Even higher strain (Da/a~3%) barriers have been used to achieve emission wavelengths as short as 3.0 m [87], although, as expected, high thermal resistance as well as low T0 and T1 values limited the CW output power to quite low values (~ 2.5 mW). Such degraded performance relative to longer wavelength QCLs may be due in-part to strong carrier leakage to satellite valleys (L, X) for ~ 3.05 m-emitting devices grown on InP, since the quantum wells for such devices require very high indium contents [88,89]. Another approach to mitigate the high strain is to employ composite barriers, allowing pulsed lasing at ~3.3 m, although leakage to satellite valleys is still an issue as evidenced by low T1 values [90].…”

Low‐strain, quantum‐cascade‐laser active regions grown on metamorphic buffer layers for emission in the 3.0–4.0 μm wavelength region

“…Finally, just as for DW [16, 17] and DW TA [18] 4.8 μm emitting QCLs, suppressed carrier leakage leads to dramatically reduced temperature sensitivity for both J th and the slope efficiency, η s , as evidenced by high values for their characteristic temperatures, T 0 and T 1 , respectively. Leakage to satellite valleys ( L , X ) are expected to contribute to only a small fraction (<3% at 3.5 μm) of the total current density at RT [38, 39]. Since both the maximum CW power, P max , and the maximum CW wall‐plug efficiency, η wp,max , are strong functions of T 0 and T 1 [8, 20], significant increases in P max and η wp,max will result for QCLs of high T 0 and T 1 values.…”