Hole‐blocking mechanism in high‐gain avalanche rushing amorphous photoconductor (HARP) film

Kikuchi, Kenji; Ohkawa, Yuji; Miyakawa, Kazunori; Matsubara, Takehiro; Tanioka, Kenkichi; Kubota, Minoru; Egami, Norifumi

doi:10.1002/pssc.201084055

Cited by 35 publications

(23 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The cause of this large increase is considered to be due to many oxygen vacancies in the Ga 2 O 3 layer because no oxygen is supplied during the deposition. The defect levels due to oxygen vacancies in the hole-blocking layer make the effective barrier height for holes lower than the theoretical value [38]. For the purposes of minimizing dark current J, the optimum partial pressure of oxygen was 6.0 × 10 −2 Pa in our growth conditions.…”

Section: Resultsmentioning

confidence: 97%

Photocurrent multiplication in Ga2O3/CuInGaSe2 heterojunction photosensors

Kikuchi¹,

Imura²,

Miyakawa³

et al. 2015

Sensors and Actuators A: Physical

Self Cite

View full text Add to dashboard Cite

Section: Resultsmentioning

confidence: 97%

Photocurrent multiplication in Ga2O3/CuInGaSe2 heterojunction photosensors

Kikuchi¹,

Imura²,

Miyakawa³

et al. 2015

Sensors and Actuators A: Physical

Self Cite

View full text Add to dashboard Cite

“…21 Recently, various n-type organic polymers with low temperature deposition, e.g., C60 doped polymer and perylenetetracarboxylic bisbenzimidazole (PTCBI) have been used with direct conversion a-Se but have not supported electric fields (E Se ) greater than 45 V/µm. 22,23 In this work, we present the first avalanche-gain measurements from a p-i-n HARP structure fabricated using deposition methods scalable to large area.…”

Section: C Large Area Harp For Medical Imagingmentioning

confidence: 99%

Development of solid‐state avalanche amorphous selenium for medical imaging

et al. 2015

View full text Add to dashboard Cite

Purpose: Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. Methods: The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. Results: An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. Conclusions: We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel. C 2015 American Association of Physicists in Medicine.

show abstract

“…HARP amplifies the photogenerated charge before the signal is readout in the TFT array. High definition a-Se based HARP cameras have been successfully used in broadcast for over two decades [16][17][18] . However , we have only recently shown the first avalanche gain measurements for an a-Se solid state HARP structure 19,20 which utilized a commercial facility for large area a-Se deposition.…”

Section: Existing A-se Detector Technologymentioning

confidence: 99%

SWAD: inherent photon counting performance of amorphous selenium multi-well avalanche detector

2016

View full text Add to dashboard Cite

Photon counting detectors (PCDs) have the potential to improve x-ray imaging, however they are still hindered by several performance limitations and high production cost. By using amorphous Selenium (a-Se) the cost of PCDs can be significantly reduced compared to crystalline materials and enable large area detector fabrication. To overcome the problem of low carrier mobility and low charge conversion gain in a-Se, we are developing a novel direct conversion aSe field-Shaping multi-Well Avalanche Detector (SWAD). SWAD circumvents the charge transport limitation by using a Frisch grid built within the readout circuit, reducing charge collection time to ~200 ns. Field shaping permits depth independent avalanche gain in wells, resulting in total conversion gain that is comparable to Si and CdTe. In the present work we investigate the effects of charge sharing and energy loss to understand the inherent photon counting performance for SWAD at x-ray energies used in breast imaging applications (20-50keV). The energy deposition profile for each interacting x-ray was determined with Monte Carlo simulation. For the energy ranges we are interested in, photoelectric interaction dominates, with a k-fluorescence yield of approximately 60%. Using a monoenergetic 45 keV beam incident on a target pixel in 400um of a-Se, our results show that only 20.42 % and 22.4 % of primary interacting photons have kfluorescence emissions which escape the target pixel for 100um and 85um pixel sizes respectively, demonstrating SWAD's potential for high spatial resolution applications.

show abstract

Hole‐blocking mechanism in high‐gain avalanche rushing amorphous photoconductor (HARP) film

Cited by 35 publications

References 6 publications

Photocurrent multiplication in Ga2O3/CuInGaSe2 heterojunction photosensors

Photocurrent multiplication in Ga2O3/CuInGaSe2 heterojunction photosensors

Development of solid‐state avalanche amorphous selenium for medical imaging

SWAD: inherent photon counting performance of amorphous selenium multi-well avalanche detector

Contact Info

Product

Resources

About