Mark Y. Su

Single-photon detection using a quantum dot optically gated field-effect transistor with high internal quantum efficiency

We investigate the operation of a quantum dot, optically gated, field-effect transistor as a photon detector. The detector exhibits time-gated, single-shot, single-photon sensitivity, a linear response, and an internal quantum efficiency of up to (68±18)% at 4K. Given the noise of the detector system, they find that a particular discriminator level can be chosen so the device operates with an internal quantum efficiency of (53±11)% and dark counts of 0.003 counts per shot.

Operational Analysis of a Quantum Dot Optically Gated Field-Effect Transistor as a Single-Photon Detector

We report on the operation of a novel single-photon detector, where a layer of self-assembled quantum dots (QDs) is used as an optically addressable floating gate in a GaAs/Al0.2Ga0.8As delta-doped field-effect transistor. Photogenerated holes charge the QDs, and subsequently, change the amount of current flowing through the channel by screening the internal gate field. The photoconductive gain associated with this process makes the structure extremely sensitive to light of the appropriate wavelength. We investigate the charge storage and resulting persistent photoconductivity by performing time-resolved measurements of the channel current and of the photoluminescence emitted from the QDs under laser illumination. In addition, we characterize the response of the detector, and investigate sources of photogenerated signals by using the Poisson statistics of laser light. The device exhibits time-gated, single-shot, single-photon sensitivity at a temperature of 4 K. It also exhibits a linear response, and detects photons absorbed in its dedicated absorption layer with an internal quantum efficiency (IQE) of up to (68 plusmn18)%. Given the noise of the detection system, the device is shown to operate with an IQE of (53 plusmn 11)% and dark counts of 0.003 counts per shot for a particular discriminator level.

Enhanced light extraction from circular Bragg grating coupled microcavities

A 7-fold enhancement of light extraction from a vertical-cavity light-emitting diode structure over a 130 nm bandwidth at room temperature was achieved using circular Bragg gratings. The enhancement factor corresponded to a 41% external efficiency.

Designing high electron mobility transistor heterostructures with quantum dots for efficient, number-resolving photon detection

We describe the design of the epitaxial layers for an efficient, photon-number-determining detector that utilizes a layer of self-assembled quantum dots as an optically addressable gate in a field-effect transistor. Our design features a dedicated absorption layer where photoexcited holes are produced and directed with tailored electric fields to the quantum dot layer. A barrier layer ensures that the quantum dot layer is located at a two-dimensional potential minimum of the structure for the efficient collection of holes. Using quantum dots as charge traps allows us to contain the photoexcited holes in a well-defined plane. We derive an equation for a uniform size of the photon signal based on this precise geometry. Finally, we show corroborating data with well-resolved signals corresponding to different numbers of photons.

Photon-number-resolving capabilities of a semiconductor quantum dot, optically gated, field-effect transistor

We demonstrate the photon-number-resolving capabilities of a novel quantum dot, optically gated, field-effect transistor cooled to 4 K. Peaks are observed in the detector¿s response to highly attenuated laser pulses in accordance with Poisson statistics.

Photon-number discrimination using a semiconductor quantum dot, optically gated, field-effect transistor

We demonstrate photon-number discrimination using a novel semiconductor detector that utilizes a layer of self-assembled InGaAs quantum dots (QDs) as an optically addressable floating gate in a GaAs/AlGaAs δ-doped field-effect transistor. When the QDOGFET (quantum dot, optically gated, field-effect transistor) is illuminated, the internal gate field directs the holes generated in the dedicated absorption layer of the structure to the QDs, where they are trapped. The positively charged holes are confined to the dots and screen the internal gate field, causing a persistent change in the channel current that is proportional to the total number of holes trapped in the QD ensemble. We use highly attenuated laser pulses to characterize the response of the QDOGFET cooled to 4 K. We demonstrate that different photon-number states produce well resolved changes in the channel current, where the responses of the detector reflect the Poisson statistics of the laser light. For a mean photon number of 1.1, we show that decision regions can be defined such that the QDOGFET determines the number (0, 1, 2, or ≥3) of detected photons with a probability of accuracy ≥83 % in a single-shot measurement.

Single-photon detection using a semiconductor quantum dot, optically gated, field-effect transistor

We demonstrate the operation of a novel quantum dot, optically gated, field-effect transistor as a photon detector. The device is shown to exhibit single-photon sensitivity, a linear response, and an internal quantum efficiency of ~73 %.

Enhanced mode extraction in AlO/sub x//GaAs microcavity pillars and circular gratings

Here we report enhanced spontaneous emission intensity in AlOx/GaAs micropillars with InGaAs quantum dot (QD) ensemble emitters, measured using photoluminescence (PL). The PL from the QD ensemble was emitted into discrete transverse micropillar modes. We then measured the PL spectrum of pillars whose outer rim is replaced with an increasing number of concentric rings to form a high-order circular grating. As more periods were added to the grating, narrow transverse micropillar mode emission was suppressed and became dominated by a broad grating-extracted mode.