Defect filtering for thermal expansion induced dislocations in III–V lasers on silicon

Abstract

Growing III-V semiconductor lasers directly on silicon circuitry will transform information networks. Currently, dislocations limit performance and lifetime even in defect tolerant InAs quantum-dot (QD)-based devices. Although the QD layers are below the critical thickness for strain relaxation, they still contain long, previously unexplained misfit dislocations which lead to significant non-radiative recombination. This work offers a mechanism for their formation, demonstrating that the combined effects of thermal-expansion mismatch between the III-V layers and silicon and precipitate and alloy hardening effects in the active region generate the misfit dislocations during sample cooldown following growth. These same hardening effects can be leveraged to mitigate the very problem they create. The addition of thin, strained, indium-alloyed trapping layers displaces 95% of the misfit dislocations from the QD layer, in model structures. In full lasers, performance benefits from adding trapping layer now both above and below the QD layers include a twofold reduction in lasing threshold currents and a threefold increase in output powers. These improved structures may finally lead to fully integrated, commercially viable siliconbased photonic integrated circuits. MAINSilicon-based photonic integrated circuits will dramatically increase data network bandwidth and energy efficiency and enable new paradigms in chip-scale sensing, detection, and ranging. Direct crystal-growth methods integrating III-V semiconductor lasers with silicon promise cost-effectiveness and scalability, [1] however, fabricating reliable, highperformance GaAs-or InP-based lasers on silicon has proven challenging. [2][3][4] Lattice constant mismatch between the silicon substrate and III-V film generates dislocation line defects, including 'threading' dislocations, which rise upward through the film. [4] Where they intersect the device's active region, they facilitate non-radiative recombination, degrading performance. The energy released causes dislocations to lengthen during device operation, a run-away degradation process ending in device failure. [2,[5][6][7] Despite decades of work to reduce threading dislocation densities to 10 6 -10 7 cm -2 (refs [8-10]) [8][9][10] and to develop dislocation-tolerant active materials such as InAsquantum dots (QDs) in quantum wells (QW) (dots in a well or DWELL), [11][12][13][14][15][16][17] threading dislocations continue to stifle the development of commercially viable III-V lasers on Si. [7,18,19] We have recently identified the root of this contradiction using plan-view scanning transmission electron microscopy (PV-STEM): unexpected dislocations found lying flat along the uppermost and lowermost QD layers, in even record lifetime QD lasers. [20,21]

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

“…While neither of the effects are obvious on small wafers that are normally used in research laboratories, scaling to 300 mm wafers in real applications makes this a concern. In addition, CTE mismatch, together with the existence of TDs, is also responsible for the formation of MDs above and below the active region through a nonconventional mechanism, as shown in the schematic in Figure a,b . During the postgrowth cooling process, the III–V layers experience tension from the CTE mismatch.…”

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).…”

“…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). This misfit growth appears to be the dominant failure mechanism for QD lasers grown on silicon substrates.…”

GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications

“…As germanium material has lattice parameter and thermal expansion coefficient close to those of the GaAs, a common strategy is to benefit from all the Ge heteroepitaxy on silicon developments to reduce the structural defects in the GaAs layer [31,41,[51][52][53]. This way, we avoid additional threading dislocation nucleation.…”

“…TDs are likely to be transferred from MDs when the distance to the sample edge is much longer than the distance to the epi-layer surface. Meanwhile, TDs could also transfer to MDs either through dislocation glides, extending the misfit segment beneath it, or in active region during the electron-hole recombination through the phenomenon known as recombination-enhanced dislocations motion [31]. Typically, in the growth of GaAs on Si, the TDD is around 10 10 cm À2 at the growth interface [32].…”