Influence of zinc diffusion on the optical performance of heterogeneously integrated C-band lasers

In this work, we investigate the impact of contact annealing on the device performance of C-band laser diodes micro-transfer printed onto a silicon photonics platform. Annealing allows reducing the contact resistance of the devices but can also have an impact on the diffusion of dopants towards the active region, decreasing the quantum efficiency of the laser. This trade-off is studied in this paper. Through capacitance deep-level transient spectroscopy (C-DLTS) analysis, the decrease in performance upon annealing is associated with zinc impurities. These defects are believed to diffuse toward the active region, and as a result, act as non-radiative recombination centers. To eliminate the influence of the micro-transfer printing step, two sets of devices were compared. Both were fabricated from the same epitaxial wafer and underwent identical processing, except that one set was characterized before transfer-printing on the native substrate, whereas the other was measured after being transfer-printed onto silicon. C-DLTS measurements confirmed that the same process occurs on native InP substrates. Once the device contacts are annealed, constant current stress testing does not introduce further substantial threshold current variations.