Résumé
Monolithic integration of mid-infrared (MIR) light sources on cheap and large Si substrates would enable low-cost, high-volume device production and pave the way for MIR photonic sensors on Si photonic integrated circuits. However, the large difference between Si and most III-V materials leads to the formation of a high defect density [1]. In particular, dislocations are non-radiative recombination centers and introduce trap levels in the bandgap, leading to performance degradation as evidenced by an increase in threshold current [2] and reduced lifetime. Several solutions have been investigated to overcome this limitation, including the use of defect-tolerant active design. Recent studies [3,4] have shown that interband cascade lasers (ICLs) appear to be the leading MIR light sources on Si due to their special design, as they exhibit similar behavior to their native substrate around 3.3 µm. In this study, we begin to explore the tolerance window of ICLs by moving towards longer wavelengths. We have fabricated ICLs designed to emit at 4.2 and 4.6 µm, grown simultaneously on GaSb, GaAs and (001) Si substrates. They consist of an active zone comprised between two n-doped InAs/AlSb superlattice claddings and two n-type GaSb confinement layers. For both designs we observe a broadening of the satellite peaks of the high resolution X-ray diffraction (HR-XRD) patterns (Fig. 1a) for ICLs on GaAs and Si, indicating a high dislocation density, estimated by electron contrasting channeling imaging (ECCI) to be around 3 - 4 x 108 cm-2 for all structures (Fig. 1b and 1c). The structures are then processed in 8 µm x 2 mm lasers and studied in continuous wave (CW) mode. Their electro-optical characteristics show that, at room temperature, the threshold current on GaAs and Si is similar to that on GaSb at 4.2 µm (Fig. 2a), while there is a difference at 4.6 µm (Fig. 2b). Nevertheless, aging of these ICLs (Fig. 3) close to the maximum operating temperature (30°C at 4.2 µm and 25°C at 4.6 µm) shows no degradation of the initial threshold current and optical power after 500 h, demonstrating the tolerance of the ICLs over a wide wavelength range. Further studies will be carried out to understand this phenomenon.