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Electrically Driven Photonic Crystal Cavities Yield Low-power Optoelectronic Devices
Published 2012 · Physics
Optical interconnects in next-generation computing promise major performance enhancements and vast reductions in system power consumption. Present embodiments of optical information transmission range from traditional long-haul fiber-optics to intra-data center communication. To scale further—to intraboard or on-chip optical interconnects—appropriate semiconductor sources must be developed. And to be competitive with pre-existing electrical interconnects, optical links should aim for a total energy target of 10 femto-Joules per bit (fJ/bit).1 To attain the proper targets for low power consumption and speed, photonic crystal cavity devices have been explored as potential solutions.2 By possessing a wavelength-size cavity, the amount of dielectric material that must be controlled for a desired function is reduced, as is the corresponding energy. Until now, the ability to electrically harness the superior capabilities of photonic crystal cavities has remained elusive because of complicated fabrication procedures.3 We have developed a new platform to form a lateral p-i-n junction in gallium arsenide (GaAs) that efficiently controls cavities and enables ultra-low power operation of lasers, LEDs, and modulators. Our approach to solving the problem of electrical injection into 2D polycarbonate membranes is to use a lateral junction formed by ion implantation: see Figure 1(a).4 This contrasts with previous vertical junction approaches as the current pathway can be lithographically defined with high precision. We used a series of aligned electron-beam lithography steps along with optimized ion implantation and thermal annealing recipes to create devices: see Figure 1(b). A typical room temperature current-voltage plot—see Figure 1(c)—shows excellent rectifying diode behavior. Current densities above 10kA/cm 2 Figure 1. Fabrication design and performance of electrically driven photonic crystal cavity devices. (a) Schematic layout of devices. The doping regions (labeled in green for n-type and red for p-type) are tapered towards the cavity center to provide efficient electrical injection. (b) Tilted angle scanning electron microscope (SEM) image of a fabricated device. The doping regions are partially visible with the SEM coloration. (c) Current-voltage plot for a typical device at room temperature showing four orders of magnitude on-off ratio. (d) Current in-light out plot for our quantum dot laser at 50K (blue) and 150K (green). Black lines are linear fits of the laser threshold, with the inset showing an IR camera picture of a lasing device above threshold. (e) Directly modulated LED emission from a room temperature device for two different bit sequences. AU: Arbitrary units.