This proposal addresses the need for advancements in solid state detector technologies for use in quantum information science systems. In particular, there is a need for the development of novel photodetector systems that simultaneously exhibit high speed (i.e., frequency bandwidth in excess of 5 GHz) as well as high quantum efficiency (QE in excess of 99%) at or near traditional telecommunications wavelengths (~1.55 microns). Conventional detectors, i.e. p-i-n photodiodes, can readily be designed to meet the frequency bandwidth target at the cost of low QE, or the QE target at the cost of low bandwidth, but the simultaneous achievement of both characteristics is beyond their capability. For example, high quantum efficiency can be achieved simply by incorporating an absorbing region which is sufficiently thick relative to the absorption length of incident photons. However, the long minority carrier transit time associated with a thick active region inherently limits the frequency bandwidth of such a device. Conversely, minority carrier transit time can be decreased and frequency bandwidth can be increased by thinning the active light absorbing region, but in a conventional detector, the associated decrease in absorption probability limits QE. Amethyst Research proposes to overcome this limitation of conventional detectors through the application of its novel Resonant Cavity Enhanced Photodetector (RCE-PD) technology. A resonant cavity enhanced photodetector essentially consists of a thin optical absorption layer located in an optical cavity between two distributed Bragg reflectors. The thin optical absorption layer allows for a short minority carrier transit time and thus high frequency bandwidth. At the same time, the optical cavity structure created by the distributed Bragg reflectors causes light to recirculate inside the cavity, thereby enhancing the probability of absorption and resulting in high quantum efficiency. Thus, unlike a conventional p-i-n detector, Amethyst's RCE-PD technology is capable of supporting the high speed as well as high QE requirements of this program. Amethyst, in partnership with semiconductor material growth experts at the University of Oklahoma, will apply its knowledge and experience to design, optimize, grow, fabricate, and characterize a GaSb-based RCE-PD device suitable for DOE's quantum information science needs at the conventional telecom wavelength of 1.55 microns. The RCE-PD will be designed to simultaneously exhibit quantum efficiency >99% at the design wavelength of 1.55 microns as well as frequency bandwidth >5 GHz. The specific motivation for this research is to develop quantum sensors and controls to enable emerging scientific applications. We also note that a tremendous commercialization opportunity exists because of the 1.55 micron wavelength compatibility between this new technology and the enormous volume of already in-place conventional telecommunications infrastructure. Finally, we note that with careful engineering, the RCE-PDâs resonant detection wavelength can be tuned across the entire infrared range (from 1-20 microns). Because of this flexibility, the resonant cavity approach in general offers additional engineering freedom as it can readily be adapted to serve a wide set of applications including optical communications, spectroscopic trace gas sensing, and real-time chemical signature monitoring
