2, Intel Corporation, Santa Clara, California, United States
Quantum dot (QD) lasers epitaxially grown on Si are a promising light source on Si because effective lateral carrier confinement makes the lasers much less sensitive to the large dislocation densities that inevitably arise in III-V epitaxy on Si. For the past decade, considerable progress has been made to enhance the performance as well as reliability of the QD lasers.1 Here, we present recent improvements in the reliability of the QD lasers with an extrapolated mean-time-to-failure of more than a million hours, which was enabled by a low threading dislocation density (TDD) GaAs buffer layer.
The performance of QD narrow-ridge waveguide lasers was first characterized. We have achieved continuous-wave (CW) threshold current as low as 6.2 mA and output powers up to 185 mW at 20 °C from the QD lasers grown on an optimized GaAs/Si template. Two techniques: thermal cycle annealing and InGaAs/GaAs dislocation filter layers were employed to reduce the dislocation density from ~3×108 cm-2 in past lasers to 7×106 cm-2 in these lasers, which is a factor of ~40 reduction.2
QD lasers were prepared for lifetime tests by mounting and wirebonding them onto AlN carriers. The lasers mounted on the carriers were tested at Intel Corp. at 35 °C under constant current mode. The driving currents ranged from 30 – 50 mA in order to age the lasers at roughly 2× the initial threshold currents of each laser. LIV sweeps were performed periodically during the aging test to monitor the changes in the threshold current and slope efficiency. From a nonlinear fitting method commonly used in the literature,1 the extrapolated device mean-time-to-failure (time to double the initial threshold current) is more than one million hours (~114 years). The degradation in the slope efficiency is also studied and the average extrapolated mean-time-to-double the bias current for 10 mW output power is also more than one million hours. We also present the trend of the QD laser reliabilities depending on the threading dislocation densities in the GaAs/Si templates. The QD lasers grown on the TDD= 7×106 cm-2 GaAs/Si template achieved roughly three and five orders of magnitude higher extrapolated lifetimes than those grown on the TDD= 7×107 cm-2 and the TDD= 3×108 cm-2 templates, respectively.
Plan-view transmission electron microscopy showed a relatively high density of misfit dislocations in the QD laser active regions. Compared to the unaged device, the aged device revealed radiation-enhanced dislocation climbs, which are considered as the main gradual degradation mechanism. To achieve even higher reliability, a misfit-free QD laser on Si is going to be investigated and tested at higher aging currents and elevated temperatures.
1. A. Y. Liu, et al. IEEE J. of Sel. Top. In Quan. Elec. 21, 1900708, 2015
2. D. Jung, et al. Appl. Phys. Lett. 111, 122107, 2017