A Near-Infrared Enhanced Silicon Single-Photon Avalanche Diode With a Spherically Uniform Electric Field Peak

Abstract

A near-infrared (NIR) enhanced silicon single-photon avalanche diode (SPAD) fabricated in a customized 0.13 µm CMOS technology is presented. The SPAD has a depleted absorption volume of approximately 15 µm × 15 µm × 18 µm. Electrons generated in the absorption region are efficiently transported by drift to a central active avalanche region with a diameter of 2 µm. At the operating voltage, the active region contains a spherically uniform field peak, enabling the multiplication of electrons originating from all corners of the device. The advantages of the SPAD architecture include high NIR photon detection efficiency (PDE), drift-based transport, low afterpulsing, and compatibility with an integrated CMOS readout. A front-side illuminated device is fabricated and characterized. The SPAD has a PDE of 13% at wavelength 905 nm, an afterpulsing probability < 0.1% for a dead time of 13 ns, and a median dark count rate (DCR) of 840 Hz at room temperature. The device shows promising performance for time-of-flight applications that benefit from uniform NIR-sensitive SPAD arrays.

A Backside-Illuminated Charge-Focusing Silicon SPAD with Enhanced Near-Infrared Sensitivity

“…The BSI SPAD was designed based on the architecture of a previously reported FSI device [9], and it was manufactured in a customized 130 nm CMOS technology. The backside processing was executed roughly according to the flow described by B. Vereecke et al [24].…”

“…The circuits also contain digital counters (CN) and output buffers for monitoring breakdown events. Reference [9] describes the operation of the readout. Besides, for the purpose of current-voltage (IV) characterization, array modules are also available in which the central cathodes are directly connected to contact pads without integrated readout.…”

“…However, the larger band gap also leads to a relatively low absorption coefficient for NIR photons [8]. Due to the inefficient absorption of infrared light, silicon SPADs may require an absorption volume with a depth exceeding 5 µm to achieve a PDE above 10% at 905nm [9][10][11][12][13][14][15][16].…”

“…Additionally, optical microlenses can be introduced for focusing light into the volume below the multiplication region [11]. Furthermore, SPADs have been demonstrated containing charge-focusing electric fields that funnel charges generated in the peripheral volume, including the guard ring, into the multiplication region [9,12,21]. In these devices, carriers generated close to the edges of the SPAD can also reach the multiplication field, which significantly enhances the PDE.…”

“…In this work, we present a BSI silicon SPAD with state-of-the-art NIR efficiency. The device architecture is based on a previously reported frontside illuminated (FSI) SPAD [9]. The detector contains a deep depleted absorption volume with a charge-focusing electric field.…”