Abstract
We compared the performance of ICLs with different active zone designs (type-I or type-II QW). The type-I ICL showed higher performance than the conventional design, with lower threshold currents and higher operating temperature. These results are promising for improving laser performance at short wavelengths. In recent decades, interband cascade lasers (ICLs) have emerged as the leading mid-infrared source, with a performance sweet spot between 3 and 4 µm. Extensive studies have been carried out to extend their operating wavelength range [1]. In contrast, little work has been done at shorter wavelengths, where most applications use type-I laser diodes. However, their performance degrades significantly above 2.5 µm [2]. In this case, developing ICLs in this range could improve laser performance and cover the 2.5 – 3 µm range. In this work, we compare the performance of ICLs using type-I and type-II QWs. Both lasers are designed to emit at 2.7 µm, the first one with a GaInAsSb QW and the second with a conventional W-QW. The structures are grown by molecular beam epitaxy on GaSb substrates and consist of a 5-stage active zone, comprised between two n-doped InAs/AlSb superlattice claddings and two n-doped GaSb separate confinement heterostructures. The lasers are then processed into 100 µm x 2 mm and 8 µm x 2 mm Fabry-Perot cavities using standard photolithography and etching techniques. The type-I and type-II ICLs were studied in the pulsed regime at 20°C and showed threshold current densities of 100 A/cm² and 360 A/cm², respectively (Figure 1). In CW operation, both structures share a common characteristic temperature of 44 K, but the type-I ICL operates at less than half the threshold current of the type-II ICL. In addition, the maximum operating temperature was of 70°C, whereas the type-II ICL does not exceed 55°C (Figure 2). A study as a function of the cavity length showed that the internal losses were the same for both structures (7 cm-1), but the internal quantum efficiency was much better in the type-I ICL (208%) than in the type-II structure (116%). This result was expected as the recombination probability is higher in a type-I QW due to the better wavefunction overlap. These initial results show that while the performance of the conventional ICL design is limited below 3 µm, type-I ICLs open the way to high-performance lasers in the 2.5 – 3 µm range.