April 2007

EEEL Demonstrates Semiconductor Photon-Number-Resolving Detector

Researchers in the Optoelectronics Division's Nanostructure Fabrication and Metrology Project have developed a single-shot, single-photon detector using a semiconductor quantum dot, optically gated, field-effect transistor (QDOGFET).  They have demonstrated the photon-number-resolving capabilities of this unique detector, important for quantum information and metrology applications.

EEEL researchers Mary Rowe, Eric Gansen, Marion Greene, Todd Harvey, and Rich Mirin developed, fabricated and tested the QDOGFET detector, which consists of a GaAs/AlGaAs, delta-doped field-effect transistor (FET) with a layer of InGaAs quantum dots (QDs) acting as an optically addressable floating gate.  The structure was grown by molecular beam epitaxy on a GaAs substrate and is designed to efficiently detect photons transmitted by the semitransparent gate and absorbed in the GaAs region separating the QDs and the two-dimensional electron gas (2DEG).  With a reverse bias applied to the gate, photo-excited holes are swept by the internal electric field toward the QD layer, where they are trapped, while the corresponding electrons are swept in the opposite direction, where they join the 2DEG.  Confined to the QDs, the positively charged holes screen the internal electric field for as long as they are stored in the dots and subsequently cause an increase in channel current.

The QDOGFET detector exhibits sensitivity to single photons of light tuned above the bandgap of GaAs.  Recently the detector was shown capable of resolving the number of photons in an attenuated optical pulse.  When illuminated with weak laser pulses, discrete photon-number states produced well-resolved changes in the channel current, where the responses of the detector reflected the Poisson statistics of the laser light.   Analysis of the detector’s responses indicated that, on average, each trapped hole from an absorbed photon changes the channel current by 0.34 ± 0.01 nA, in good agreement with theoretical calculations specific to the device geometry.  The detector is highly linear with photon number.  It exhibits an internal quantum efficiency (ratio of trapped holes to absorbed photons) of 68 ± 18 %, a record high for FET-type single photon detectors.  Currently, the external quantum efficiency (ratio of trapped holes to photons incident on the detection window) of the detector is limited to about 6 %.  Future work will include incorporating the device into a resonant cavity and increasing the size of the detection area to improve the coupling efficiency.

Single-photon detectors are critical components for quantum optics and quantum cryptography, and are at the frontiers of low-light imaging in medicine, astronomy, and chemistry.  Photon-number-resolving detectors are an enabling technology for quantum optical metrology and can verify the quality of single-photon sources and significantly extend the length of secure links in quantum key distribution systems.  Semiconductor single photon detectors open the possibility of high-temperature operation and monolithic integration with electronics.  Support for this project has been provided by DTO.

Contact:  Rich Mirin, phone 303-497-7955