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Triet Ho LT, Mukherjee A, Vasileska D, Akis J, Stavro J, Zhao W, Goldan AH. Modeling Dark Current Conduction Mechanisms and Mitigation Techniques in Vertically Stacked Amorphous Selenium-Based Photodetectors. ACS APPLIED ELECTRONIC MATERIALS 2021; 3:3538-3546. [PMID: 35600494 PMCID: PMC9119575 DOI: 10.1021/acsaelm.1c00444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Amorphous selenium (a-Se) with its single-carrier and non-Markovian, hole impact ionization process can revolutionize low-light detection and emerge to be a solid-state replacement to the vacuum photomultiplier tube (PMT). Although a-Se-based solid-state avalanche detectors can ideally provide gains comparable to PMTs, their development has been severely limited by the irreversible breakdown of inefficient hole blocking layers (HBLs). Thus, understanding of the transport characteristics and ways to control electrical hot spots and, thereby, the breakdown voltage is key to improving the performance of avalanche a-Se devices. Simulations using Atlas, SILVACO, were employed to identify relevant conduction mechanisms in a-Se-based detectors: space-charge-limited current, bulk thermal generation, Schottky emission, Poole-Frenkel activated mobility, and hopping conduction. Simulation parameters were obtained from experimental data and first-principle calculations. The theoretical models were validated by comparing them with experimental steady-state dark current densities in avalanche and nonavalanche a-Se detectors. To maintain bulk thermal generation-limited dark current levels in a-Se detectors, a high-permittivity noninsulating material is required to substantially decrease the electric field at the electrode/hole blocking layer interface, thus preventing injection from the high-voltage electrode. This, in turn, prevents Joule heating from crystallizing the a-Se layer, consequently avoiding early dielectric breakdown of the device.
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Affiliation(s)
- Le Thanh Triet Ho
- Department of Electrical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York 11794, United States
| | - Atreyo Mukherjee
- Department of Electrical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York 11794, United States
| | - Dragica Vasileska
- School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - John Akis
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
| | - Jann Stavro
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
| | - Wei Zhao
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
| | - Amir H Goldan
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
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Mukherjee A, Vasileska D, Akis J, Goldan AH. Monte Carlo Solution of High Electric Field Hole Transport Processes in Avalanche Amorphous Selenium. ACS OMEGA 2021; 6:4574-4581. [PMID: 33644565 PMCID: PMC7905821 DOI: 10.1021/acsomega.0c04922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 12/22/2020] [Indexed: 06/12/2023]
Abstract
Amorphous selenium lacks the structural long-range order present in crystalline solids. However, the stark similarity in the short-range order that exists across its allotropic forms, augmented with a shift to non-activated extended-state transport at high electric fields beyond the onset of impact ionization, allowed us to perform this theoretical study, which describes the high-field extended-state hole transport processes in amorphous selenium by modeling the band-transport lattice theory of its crystalline counterpart trigonal selenium. An in-house bulk Monte Carlo algorithm is employed to solve the semiclassical Boltzmann transport equation, providing microscopic insight to carrier trajectories and relaxation dynamics of these non-equilibrium "hot" holes in extended states. The extended-state hole-phonon interaction and the lack of long-range order in the amorphous phase is modeled as individual scattering processes, namely acoustic, polar and non-polar optical phonons, disorder and dipole scattering, and impact ionization gain, which is modeled using a power law Keldysh fit. We have used a non-parabolic approximation to the density functional theory calculated valence band density of states. To validate our transport model, we calculate and compare our time of flight mobility, impact ionization gain, ensemble energy and velocity, and high field hole energy distributions with experimental findings. We reached the conclusion that hot holes drift around in the direction perpendicular to the applied electric field and are subject to frequent acceleration/deceleration caused by the presence of high phonon, disorder, and impurity scattering. This leads to a certain determinism in the otherwise stochastic impact ionization phenomenon, as usually seen in elemental crystalline solids.
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Affiliation(s)
- Atreyo Mukherjee
- Department
of Electrical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York 11794, United States
| | - Dragica Vasileska
- School
of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - John Akis
- Department
of Radiology, School of Medicine, Stony
Brook University, Stony
Brook, New York 11794, United States
| | - Amir H. Goldan
- Department
of Radiology, School of Medicine, Stony
Brook University, Stony
Brook, New York 11794, United States
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LaBella A, Stavro J, Léveillé S, Zhao W, Goldan AH. Picosecond Time Resolution with Avalanche Amorphous Selenium. ACS PHOTONICS 2019; 6:1338-1344. [PMID: 38665849 PMCID: PMC11044824 DOI: 10.1021/acsphotonics.9b00012] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
Ultrafast photodetection has traditionally been performed with crystalline photodetectors, which tend to suffer from low production yield, suboptimal detection efficiency, and operational limitations that restrict their potential applications. Amorphous selenium is a unique, disordered photosensing material in which carrier transport can be shifted entirely from localized to extended states where holes get hot, resulting in deterministic, non-Markovian impact ionization avalanche, causing selenium to exhibit characteristics similar to crystalline photoconductors. For the first time, we have fabricated a multiwell selenium detector using nanopillars that achieves both avalanche gain and unipolar time-differential charge sensing. We experimentally show how these features together improve selenium's temporal performance by nearly 4 orders of magnitude, allowing us to achieve picosecond timing jitter suitable for a variety of ultrafast applications. Such a detector would be a viable low-cost, high production yield alternative for picosecond photodetection and imaging.
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Affiliation(s)
- Andy LaBella
- Department of Biomedical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York 11794, United States
| | - Jann Stavro
- Department of Biomedical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York 11794, United States
| | | | - Wei Zhao
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
| | - Amir H. Goldan
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, United States
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Rubel O, Baranovskii SD, Zvyagin IP, Thomas P, Kasap SO. Lucky-drift model for avalanche multiplication in amorphous semiconductors. ACTA ACUST UNITED AC 2004. [DOI: 10.1002/pssc.200304319] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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