Reduced dislocation growth leads to long lifetime InAs quantum dot lasers on silicon at high temperatures

Abstract

We describe the effectiveness of filter layers, which displace misfit dislocation (MD) formation away from the active region, in improving high temperature reliability of epitaxially integrated InAs quantum dot lasers on on-axis silicon substrates. We find that inserting these “trapping layer (TL)” filters at either 80 nm or 180 nm from the active region substantially reduces device degradation at 60 °C. After 3000 h of continuous operation, the best trapping-layer-free device shows a 55% increase in threshold current while the best trapping layer (TL) devices each show less than a 9% increase. We explain these findings by correlating changes in individual device performance to changes in misfit dislocation (MD) structure. All MDs in devices without TLs show evidence of recombination enhanced dislocation climb (REDC); in contrast, adding trapping layers at 180 nm or 80 nm reduces the fraction of electrically active MDs to 9% and 1%, respectively. Reliability data after 3000 hours suggest that incorporating trapping layers a shorter distance from the active region (80 nm) is more effective than incorporating these layers further away. We conclude by identifying the mutually and self-reinforcing failure processes associated with REDC that TLs significantly remediate: increasing dislocation line length, increasing point defect densities, and increasing junction temperature. Overall, understanding and controlling crystal defects continues to be the most impactful avenue toward integrating light sources on photonic integrated circuits and closing the gap with native-substrate lasers.

Prospects and applications of on-chip lasers

“…Notably, asymmetric step-graded (ASG) filters can efficiently reduce the TD density (TDD) to as low as 1 × 10 6 cm −2 within a 2.55 µm GaAs virtual substrate grown on (001) silicon [ 74 ]. To reduce the MDs, thin strained QWs were inserted as trapping layers (TLs) above and below the active region, which efficiently eliminated 90% of MDs away from the active region [ 75 ]. To alleviate the effects of APDs, miscut silicon substrates with a 4°–6° offcut angle have traditionally been employed to form a prominent double-stepped silicon surface, but recent breakthroughs with on-axis (001) CMOS compatible silicon substrates have demonstrated comparable or better performance.…”

Perspectives on Advances in Quantum Dot Lasers and Integration with Si Photonic Integrated Circuits

“…Copyright 2021 The Optical Society. (e) Reproduced with permission from ref . Copyright 2021 AIP Publishing.…”

“…Postaging microscopy analysis done on an older generation of samples, aged at 60 °C, has revealed the mechanism of such inserted TLs . The samples were grown on a template with 2 × 10 7 cm –2 TDD and the TLs were placed either 180 nm (TL180) or 80 nm (TL80) away from the active region.…”

A Review of the Reliability of Integrated IR Laser Diodes for Silicon Photonics

“…This misfit gr pears to be the dominant failure mechanism for QD lasers grown on silicon sub The above mentioned findings suggest that lifetime improvements of QD lasers epitaxially grown on silicon should likely proceed through the reduction in the concentration of extended defects, mainly misfit dislocations [39], or through the optimization of the carrier injection dynamics into the InAs QDs [40]. The former goal can either be achieved through the optimization of the growth procedure, of the buffer layer or through a well-engineered positioning of MD-trapping layers that prevent the formation of longitudinally extended defects in the proximity of the active region, which may happen during the heating-up and cooling-down phases of the growth process [42,43]. The introduction of misfit trapping layers, which block over 90% of the misfit dislocations which would otherwise grow along the active region [43,44], allows for a great increase in device reliability, as testified by the higher optical stability exhibited by devices featuring trapping layers within their epitaxy (Figure 9).…”