Optical communication has been proposed as a way to alleviate imminent bandwidth and energy bottlenecks in data traffic on and between Silicon integrated electronic chips. The energy consumption and data rate of optical interconnects is dependent on the performance of the transmitter and receiver end units and is not constrained by the conventional R-C limitations of microwave electrical links. Recognizing the prevalence of III-V direct-bandgap based technology for long haul and data-center interconnections, our group has developed high quality, defect-free III-V material growth on silicon for back-end-of-line integration with CMOS processes. Wurtzite-phase InP nanopillars with a high luminescence yield and low non-radiative recombination have been grown via MOCVD on 111-Silicon substrates at a low growth temperature of ~450C, without using contaminating gold catalysts. Further, selective area nucleation and growth of these nanopillars has been achieved, in order to facilitate scalable integration. This talk will focus on device demonstrations based on this material, to synthesize high performance transmitters and receivers for short-distance optical links. A highly sensitive and fast optical receiver has been demonstrated. This receiver integrates photodetection with electronic gain, in a compact bipolar junction phototransistor device showing a responsivity as high as 25 A/W. The highly scaled size enables a gain-bandwidth cutoff frequency of 375 GHz, while maintaining excellent photon absorption in an InP device. A rapidly modulated laser has been proposed as an efficient transmitter, and an InGaAs quantum-well heterostructure has been integrated in a core shell manner into the InP nanopillar to this end. The InGaAs/InP heterostructure pillars show radiative dominant recombination, with rapid carrier capture and gain at low continuous-wave pump power. A multi-quantum-well LED has been fabricated with bright emission at a Silicon transparent wavelength of 1.45 micron, and optical gain is achieved under electrical injection. Lastly, preliminary work on engineering a high-Q optical cavity is described, with the demonstration of an optically pumped nanolaser operating up to room temperature (300 K) and at Silicon transparent wavelength (1.25 micron), for integration with Silicon photonics waveguides on chip.
Indrasen Bhattacharya graduated from IIT Bombay with a BTech in EE-Honors and CS-Minor, 2012. He is currently working towards a PhD in EE (via the Applied Science and Technology graduate group), at the research group of Prof. Connie Chang-Hasnain, UC Berkeley. He has advanced to candidacy in September, 2015 and is currently in the fourth year of his PhD.