Electrical interface characteristics (I-V), optical time of flight measurements, and the x-ray (20 keV) signal response of amorphous-selenium/crystalline-silicon heterojunction structures

David M. Hunter; Chu An Ho; George Belev; Giovanni De Crescenzo; Safa O Kasap; Martin J. Yaffe

doi:10.1117/12.877738

17 March 2011 Electrical interface characteristics (I-V), optical time of flight measurements, and the x-ray (20 keV) signal response of amorphous-selenium/crystalline-silicon heterojunction structures

David M. Hunter, Chu An Ho, George Belev, Giovanni De Crescenzo, Safa O Kasap, Martin J. Yaffe

Author Affiliations +

Proceedings Volume 7961, Medical Imaging 2011: Physics of Medical Imaging; 79610X (2011) https://doi.org/10.1117/12.877738
Event: SPIE Medical Imaging, 2011, Lake Buena Vista (Orlando), Florida, United States

Abstract

We have investigated the dark current, optical TOF (time of flight) properties, and the X-ray response of amorphousselenium (a-Se)/crystalline-silicon (c-Si) heterostructures for application in digital radiography. The structures have been studied to determine if an x-ray generated electron signal, created in an a-Se layer, could be directly transferred to a c-Si based readout device such as a back-thinned CCD (charge coupled device). A simple first order band-theory of the structure indicates that x-ray generated electrons should transfer from the a-Se to the c-Si, while hole transfer from p-doped c-Si to the a-Se should be blocked, permitting a low dark signal as required. The structures we have tested have a thin metal bias electrode on the x-ray facing side of the a-Se which is deposited on the c-Si substrate. The heterostructures made with pure a-Se deposited on epitaxial p-doped (5×10 14 cm^-3) c-Si exhibited very low dark current of 15 pA cm^-2 at a negative bias field of 10 V μm^-1 applied to the a-Se. The optical TOF (time of flight) measurements show that the applied bias drops almost entirely across the a-Se layer and that the a-Se hole and electron mobilities are within the range of commonly accepted values. The x-ray signal measurements demonstrate the structure has the expected x-ray quantum efficiency. We have made a back-thinned CCD coated with a-Se and although most areas of the device show a poor x-ray response, it does contain small regions which do work properly with the expected x-ray sensitivity. Improved understanding of the a-Se/c-Si interface and preparation methods should lead to properly functioning devices.

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David M. Hunter, Chu An Ho, George Belev, Giovanni De Crescenzo, Safa O Kasap, and Martin J. Yaffe "Electrical interface characteristics (I-V), optical time of flight measurements, and the x-ray (20 keV) signal response of amorphous-selenium/crystalline-silicon heterojunction structures", Proc. SPIE 7961, Medical Imaging 2011: Physics of Medical Imaging, 79610X (17 March 2011); https://doi.org/10.1117/12.877738

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KEYWORDS

X-rays

Charge-coupled devices

Selenium

Heterojunctions

Interfaces

Electrodes

X-ray imaging

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