Abstract
Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III–V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure.
Highlights
We provide the first excess noise measurements on nanopillar-based APDs at 1.06 μm with highly localized and physically separate optical absorption and multiplication regions within a nanopillar array
The noise measurement shows a significant reduction in excess noise compared to bulk and is the first exploitation of dead space effects utilizing a 3D electric field within a nanopillar
Very large gain is achievable in the NOAAD, an APD’s maximum usable gain is that which results in the optimum signal-to-noise ratio and is determined by the excess noise factor
Summary
The nanopillar tips were subsequently exposed using the aformentioned RIE and top contacts were defined by photolithography. The exposed nanopillar tips were electrically contacted with chrome/gold (10 nm/150 nm) deposited with the substrate mounted at an angle, resulting in a self-aligned nanohole array. The excess noise was measured by illuminating the APD with a 1064nm laser (Orbits Lightwave Ethernal SlowLight) with shot noise limited RIN and measuring the noise power spectral density with a network signal analyzer (Stanford Research Systems SR780) at 100 kHz, well above 1/f noise. The amplifier and dark current noise was measured and subtracted from the APD noise under illumination. The expected shot noise was calculated from current measurements at each bias and compared to the measured noise at the same bias. The primary responsivity was calculated at the bias immediately before the measured noise began to exceed the calculated shot noise. The bandwidth was extracted from the temporal response by FFT analysis
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