CUR - The Council on Undergraduate Research

Mapping the Photoresponse of Quantum-Dot-Based Photon-Number-Resolving Detectors

Connor Govin, Trever Geerdts, and Dr. Eric Gansen, Department of Physics, University of Wisconsin La Crosse,1725 State Street, La Crosse WI 54601

Efficient and versatile single-photon detectors are fundamental to the development of future advanced communication systems. The Quantum-Dot, Optically-Gated, Field-Effect Transistor (QDOGFET) is one such detector. Utilizing tiny drops of semiconductor imbedded in a specially designed transistor, QDOGFETs have exhibited single-photon sensitivity and photon-number-resolving capabilities. A photon is detected when it photocharges a quantum dot (QD), which alters the amount of current flowing through the transistor. Since QDs within the active area produce independent and additive responses, QDOGFETs are capable of resolving the number of photons in a pulse of light. Crucial to the resolving power is that each charged QD produce the same response regardless of its location within the transistor. Here, we investigate the extent spatial nonuniformities in the QDOGFET’s response to light limit its ability to resolve individual photons. We cap the µm-sized active area of the device with a solid immersion lens (SIL) and probe the photoresponse of various groupings of QDs using an optical scanning microscope (OSM). The resulting response maps show that QDOGFETs exhibit localized “hot spots” where the devices are particularly sensitive to light. We will present experimental results that show how these hot spots depend on bias and illumination conditions and help decipher the root cause of the nonuniformities.

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