Abstract
Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries.
Highlights
The silicon microelectronics industry has developed at an exponential pace improving performance, functionality, and integration density of electronic integrated circuits
The invention of the laser in 1960 at Hughes Research Laboratories and the eventual demonstration of room temperature (RT), continuous wave lasing in a semiconductor by Alferov,[2] following simultaneous key proposals by Kroemer[3] and Alferov[4] regarding the use of double heterostructures, ushered in a impactful technological paradigm shift leading to the fields of photonics, optical communications, and the Internet
Lasers are arguably the most sensitive photonic component to material defects, and they have been demonstrated through epitaxial growth to match the performance of heterogeneously integrated devices in terms of static energy efficiency and output power
Summary
The silicon microelectronics industry has developed at an exponential pace improving performance, functionality, and integration density of electronic integrated circuits. Optical transmission has already been adopted for decades in long-haul communications and much more recently for shorter links down to the individual boards within a server rack, mostly through native substrate vertical-cavity surface-emitting laser (VCSEL) solutions, but further downscaling to within the board and eventually to on-chip interconnects has proved challenging Integrating photonics at these length scales requires small-footprint and low energy devices that are tolerant of the high temperatures sustained near the electronic processors. Quantum dots represent zero-dimensional, particle-ina-box-like quantum confined structures that can be formed through a self-assembly process using InAs on (In, Ga, Al)(As, P) layers Their artificial-atom-like properties make them ideal for low threshold, high temperature lasers, high performance semiconductor optical amplifiers (SOAs), low dark current photodetectors, and potentially high efficiency quantum confined Stark effect modulators. Applications targeting the datacom and telecom wavelength bands around 1.31 μm and 1.55 μm will be emphasized since they currently dominate ongoing research in photonic integration
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