Compact solid-state single photon detectors are regarded as enabling components in a wide range of applications such as biophotonics, tomography, homeland security, non-destructive material inspection, astronomy, and quantum key distribution. Despite the astonishing progress of these fields in recent years, there has been little progress in the performance of single photon detectors, and hence the detector is quickly becoming the bottleneck in these fields. Some of the important shortcomings of the current single photon detectors are: poor quantum efficiency, high dark count rates, lack of imaging arrays, severe cooling requirement for longer wavelengths, and low bandwidth.
Intellectual Merit: The goal of this CAREER program is to develop a novel avalanche-free single photon detector that can address most of the above problems. A new device modeling approach will be developed that is capable of modeling the micro and nano-components of this device seamlessly. The modeling will be used to optimize the epitaxial structure of the device, as well as the device geometry. Optimized devices will be evaluated, and the measurement results will be used to fine-tune the model over several cycles during the program.
Broader Impact: Realization of a high-performance single photon detector beyond visible range has a significant impact in the quality of life, manifested by its wide medical, industrial, security, and scientific applications. Also, we will incorporate some of the results of this research in the solid-state courses and advanced courses on infrared detectors. The simulation software that will be developed provides a unique avenue for the students to design detectors with nanometer size regions and see their performance during these courses. Undergraduate and graduate students from under-represented and minority groups will be encouraged to take part in this research. We plan to take advantage of Alliances for Graduate Education and the Professorate program at Northwestern University in this regard.
Short-Wave Infrared Nano-Injection Detectors and Imagers Short-wave infrared (SWIR) photon detection has become an essential technology in the modern world. It has been widely researched in both academic and commercial interests, and deployed in many medical, environmental, commercial, military systems and telecommunication applications. Currently, avalanche photodetectors (APDs) are commonly utilized when detection of single photons is needed. However, APDs require high electric fields which can lead to edge breakdown, and need large guard rings to prevent this phenomenon[i]. The guard rings increase the pixel spacing and reduces the fill factor, which in turn leads to larger imager chips, hence larger and heavier optics. Furthermore, the APD pixels need to be spaced apart to prevent cross-talk due to generation-recombination and re-emission of carriers. Hence, realization of high-resolution imagers with high internal gain and low noise has remained a challenging task for APD based imagers. In the nature, eyes are the biological counterparts of solid state imagers. Furthermore, with their superior dim light vision capabilities, the eyes rely on a very different mechanism to provide high-sensitivity photodetection. Human eye is surprisingly sensitive and is capable of detecting a few photons[ii]. The absorption of light triggers a chain of reactions that lead to the closing of the ion channels, which changes the current passing through the rod cell (see Figure 1). This detection mechanism provides both high efficiency and high sensitivity at room temperature; a condition that is very difficult to achieve in conventional single photon detectors. Simply put, the energy of a single photon is extremely small, and the only reliable way of sensing is to use a very small sensing volume, for example a quantum dot[iii]. However, the wavelength of light is significantly larger than such a sensor, and hence the interaction between the photon and the sensor, is extremely small[iv]. Any attempt to enhance the efficiency by increasing the volume would simply reduce the sensitivity. Rod cell’s detection mechanism resolves this conflict by using a micrometer-scale absorbing volume, and nano-scale sensing elements, or the ion channels. Based on the principles of the dim light vision in the eye, the researchers at the Bio-Inspired Sensors and Optoelectronic Laboratory at the Northwestern University have developed a new approach, called the nano-injection detector. Similar to the eye, the nano-injection detector uses nano-scale sensing elements (the nano-injector), which regulate the carrier flow and amplify the signal, on top of relatively large micron-scale absorbing volumes. The large absorption region ensures that the incoming photons are captured with high efficiency, which can exceed 85% in the infrared spectrum. With the nano-injection devices, extremely high photon-to-electron conversion ratios, surpassing 10,000 electrons/photon, have been achieved[v]. The devices exhibit very low noise levels, due to a novel noise suppression mechanism[vi] which decreases the noise levels to almost half of the classical noise limits[vii]. The arrays show very high uniformity with an industry-record-high timing accuracy at room temperature[viii]. As such, the nano-injection detectors can be used to track the events of interest with very high precision in timing. Under moderate cooling, the measured signal-to-noise ratio of a nano-injection imager was two orders of magnitude higher than a high–end commercial SWIR camera[ix] (Figure 3). The camera was operated at ~2000 frames/second, and the SNR analysis revealed that the overall noise of the imager was very low, at 28 electrons root-mean-square. [i] J. C. Campbell, et al, Recent advances in avalanche photodiodes, Selected Topics in Quantum Electronics, IEEE Journal of, 10(4), 777-787 (2004) [ii] S. Hecht, S. Shlaer, and M. H. Pirenne, Energy, Quanta, And Vision, Journal of. Gen. Physioogy 25, 819 (1942). [iii] S. Komiyama, et al, A single-photon detector in the far-infrared range. Nature 403, 405-407 (2000). [iv] L. Bakueva, et al, Size-tunable infrared (1000--1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer, Appl. Phys. Lett. 82, 2895 (2003) [v] O. G. Memis, et. al, A Photon Detector with Very High Gain at Low Bias and at Room Temperature, App Phys Lett, 91, 171112 (2007). [vi] A. Reklaitis, & L. Reggiani, Shot noise suppression from independently tunneled electrons in heterostructures. Semiconductor Science and Technology 14, L5-L10 (1999). [vii] O. G. Memis, et. al, Sub-Poissonian Shot Noise of a High Internal Gain Injection Photon Detector, Optics Express, 16(17), 12701 (2008). [viii] O.G. Memis, et al., On the Source of Jitter in a Room-Temperature Nanoinjection Photon Detector at 1.55 µm, IEEE Electron Device Letters, 29(8), 867 (2008). [ix] O. G. Memis, et al., Signal-to-noise performance of a short-wave infrared nanoinjection imager, Optics Letters 35(16), 2699 (2010).
