Zeyu Zhang

Monolithically integrated InAs/InGaAs quantum dot photodetectors on silicon substrates

We report InAs/InGaAs quantum dot (QD) waveguide photodetectors (PD) monolithically grown on silicon substrates. A high-crystalline quality GaAs-on-Si template was achieved by aspect ratio trapping together with the combined effects of cyclic thermal annealing and strain-balancing layer stacks. An ultra-low dark current of 0.8 nA and an internal responsivity of 0.9 A/W were measured in the O band. We also report, to the best of our knowledge, the first characterization of high-speed performance and the first demonstration of the on-chip photodetection for this QD-on-silicon system. The monolithically integrated waveguide PD shares the same platform as the previously demonstrated micro-ring lasers and can thus be integrated with laser sources for power monitors or amplifiers for pre-amplified receivers.

Compact Modeling for Silicon Photonic Heterogeneously Integrated Circuits

Photonic-integrated circuits fabricated on a heterogeneously integrated silicon platform have demonstrated record levels of integration and communication capacity. As photonic-integrated circuits become larger and more complex, designing and analyzing them demand modeling and simulation methodologies employed in matured electronic design automation. In this paper, the development of compact models for the building blocks of a fabricated optical network-on-a-chip is introduced. These models are implemented in both SPICE-compatible electronics design automation tools and dedicated photonic-circuit simulators. Model validation is conducted at both device and link levels, allowing the circuit designer to study the impact of individual device design on the overall link performance, paving the path for model-based design optimization of photonic-integrated circuits.

Semiconductor quantum dot lasers epitaxially grown on silicon with low linewidth enhancement factor

This work reports on the ultra-low linewidth enhancement factor (αH-factor) of semiconductor quantum dot lasers epitaxially grown on silicon. Owing to the low density of threading dislocations and resultant high gain, an αH value of 0.13 that is rather independent of the temperature range (288 K–308 K) is measured. Above the laser threshold, the linewidth enhancement factor does not increase extensively with the bias current which is very promising for the realization of future integrated circuits including high performance laser sources.

High performance quantum dot lasers epitaxially integrated on Si

Silicon photonics promises scalable manufacturing of integrated photonic devices through utilization of established CMOS processing techniques and facilities. Unfortunately, the silicon photonics platform lacks a viable light source, which has historically been overcome through heterogeneous integration techniques. To further improve economic viability, the platform must transition to direct epitaxy on Si to bypass the scaling limits imposed by the small sizes and high cost of III-V substrates in heterogeneous integration. InAs quantum dots have demonstrated themselves as the most promising candidate for achieving high performance light emitters epitaxially grown on Si. Using molecular beam epitaxy, we have grown quantum dot lasers composed of InAs dot-in-a-well active layers on industry-standard, on-axis (001) Si substrates. In this report, we utilized p-doping of the quantum dot active region to increase gain for improved dynamic performance and reliability. These devices have been subjected to accelerated aging conditions at 60°C and a bias multiple of twice threshold current density. After 2,750 hours of continuous aging, an extrapolated lifetime of more than 100,000 hours has been calculated.

Effects of modulation p doping in InAs quantum dot lasers on silicon

We investigate, both experimentally and theoretically, the gain characteristics of modulation p-doped 1.3 μm quantum dot lasers epitaxially grown on silicon. Gain spectra and transparency points are measured for structurally identical lasers with varying levels of p doping in the active region. A many-body model is employed to facilitate understanding of the material gain characteristics. It has been found that appropriate p doping greatly reduces transparency and improves differential gain. It is also found that the improvements saturate with excessive doping because of the increase in nonradiative carrier recombination.We investigate, both experimentally and theoretically, the gain characteristics of modulation p-doped 1.3 μm quantum dot lasers epitaxially grown on silicon. Gain spectra and transparency points are measured for structurally identical lasers with varying levels of p doping in the active region. A many-body model is employed to facilitate understanding of the material gain characteristics. It has been found that appropriate p doping greatly reduces transparency and improves differential gain. It is also found that the improvements saturate with excessive doping because of the increase in nonradiative carrier recombination.

Compact modeling and circuit-level simulation of silicon nanophotonic interconnects

Nanophotonic interconnects have been playing an increasingly important role in the datacom regime. Greater integration of silicon photonics demands modeling and simulation support for design validation, optimization and design space exploration. In this work, we develop compact models for a number of key photonic devices, which are extensively validated by the measurement data of a fabricated optical network-on-chip (ONoC). Implemented in SPICE-compatible Verilog-A, the models are used in circuit-level simulations of full optical links. The simulation results match well with the measurement data. Our model library and simulation approach enable the electro-optical (EO) co-simulation, allowing designers to include photonic devices in the whole system design space, and to co-optimize the transmitter, interconnect, and receiver jointly.