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New Development of Blocking Layer and Doping of Amorphous Selenium to Improve the Imaging Performance of Flat-Panel Imager with Avalanche Gain

C Orlik1*, A Howansky1, S Leveille2, A Mishchenko2, J Stavro1, A Goldan1, J Scheuermann1, W Zhao1, (1) Stony Brook University, Stony Brook, NY, (2) Analogic Canada, Montreal, Canada


(Tuesday, 7/14/2020) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]

Room: Track 1

Purpose: We previously demonstrated the feasibility of large area Scintillator High-Gain Avalanche Rushing Photoconductor Active Matrix Flat Panel Imager (SHARP-AMFPI), an indirect detector that utilizes avalanche amorphous selenium (a-Se) to amplify optical signal from the scintillator prior to readout. In this work, we aim to improve SHARP-AMFPI via three strategies: metal oxide hole blocking layers (HBLs) with improved electron transport, transparent bias electrode, and Te-doping of a-Se to improve optical quantum efficiency (OQE) to green light (from CsI:Ti scintillators).

Methods: Dark current of samples with new HBLs were measured at electric fields of 5 – 65 V/µm. Optical sensitivity and temporal performance were measured using a pulsed LED for both metal oxide HBL and Te-doped HARP samples. A new, large area SHARP-AMFPI prototype detector was fabricated with the following features: transparent metal oxide HBL and bias electrode, upright panel assembly allowing back-irradiation (BI) to maximize DQE of 1 mm thick flexible high-resolution CsI:Tl scintillator.

Results: The dark current of the metal oxide HBLs ranged from 10?¹¹ – 10?¹° A/cm², which is comparable to the previous SHARP-AMFPI prototype. Improved optical coupling was enabled by a combined transparency of >80% for the bias electrode and HBL. Te-doped a-Se demonstrated a factor of 3.85 increase in sensitivity to green light (522 nm) at 10 V/µm, with a 7% increase in ghosting and an increase of lag compared to a-Se without Te-doping. The temporal performance of Te-doped a-Se is expected to improve at higher electric fields.

Conclusion: The conductive metal oxide HBLs improve temporal performance compared to the insulating HBL of the previous SHARP-AMFPI prototype. Te-doped a-Se allows for higher OQE by spectral matching with CsI:Ti scintillator optical emission. The benefit of improved temporal performance and enhanced OQE will be demonstrated with the first SHARP-AMFPI with metal oxide HBL, transparent electrode, and BI geometry.

Funding Support, Disclosures, and Conflict of Interest: Research was carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704.


Flat-panel Imagers, Amorphous Selenium, Fluoroscopy


IM- X-Ray: Detector development & evaluation

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