Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Applied Physics | en_US |
| dc.contributor.advisor | Tsang, Yuen Hong (AP) | en_US |
| dc.creator | Alam, Tawsif Ibne | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13771 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Synergetic-engineered all van der waals photodiodes for fast-broadband photodetection and multifunctional optoelectronics | en_US |
| dcterms.abstract | In this report, a multifactorial study of van der Waals (vdW) photodiodes was conducted, with the aim of suppressing dark currents for ultra-low light detection, structural and contact optimization for efficient synergistic engineering of GaS-WSe2 all van der Waals (a-vdW) photodiodes. The term "all van der Waals" in this study signifies the integration of the metal contacts using van der Waals technique. The synergistically optimized device exhibit broadband detection; 275 nm - 1064 nm, multispectral unity approaching linearity, alongside a substantial LDR of 106.78 dB. Additionally, the photodiode achieve a remarkable on/off ratio of 105 and rapid response edges of 545 μs/ 471μs, exhibiting ultra-low light detection capabilities, with dark currents in the fA range, culminating in a peak responsivity of 376.78 mA/W and a detectivity of 4.12 × 1011 Jones, complemented by a EQE of 30% and a fill factor of ~ 0.33-all achieved through a single junction. For the first time, based on our analysis of multiple a-vdW devices and traditional electron beam lithography (EBL) patterned device, we highlight the importance of fermi-level pinning (FLP) free metal-2D interface engineering for GaS based photodiodes, that enables effective modulation of the Schottky barrier height via vdW metal contacts and employ meticulous thickness-engineered layers in developing a robust depletion region within the type-II GaS-WSe2 heterojunction, ultimately achieving a favorable balance among photocarrier generation-recombination, separation, transport, and extraction. | en_US |
| dcterms.abstract | We analyze and compare key figure of merits such as power exponent α and recombination order β and its evolution in multiple devices to achieve near unity value in a-vdW device, portraying recombination-trapping resilient operation, while a similar device having patterned with EBL shows significant degradation to the value of α. This suggests most of the recombination-trapping and degradation of performance occurs at the metal-2D interface, asserting our claim of renewed thinking for contact integration strategies to 2D photodiodes. Additionally, power conversion efficiency analysis along with the measured fermi-level alignment at the heterojunction of our a-vdW devices suggest the importance of achieving the perfect thickness engineered layers for realizing a robust p-n junction, balancing photocarrier generation-recombination, separation, transport, and extraction. | en_US |
| dcterms.abstract | Moreover, due to the excellent photovoltaic performance of the photodiode, it was utilized for demonstration of multi-band imaging applications as a single pixel detector. Additionally, owing to the FLP free metal contacts, excellent gate tunable open circuit voltage was achievable and the device was utilized for demonstration of gate tunable optoelectronic logic AND gate, paving the way for a single device to be used for multi-functional optoelectronics. | en_US |
| dcterms.abstract | Additionally, Schottky junction based Gr-GaS-Au photodiodes fabricated utilizing the a-vdW method demonstrated a novel double spiking photocurrent temporal response like that of pyroelectric detectors, under ultra-low light conditions, with a maximum spiking responsivity of 0.7A/W, with rise and fall time of 15ms and 36 ms respectively. | en_US |
| dcterms.abstract | Our comprehensive investigation not only advances the understanding of a-vdW heterojunction photodiodes from the perspective of contact induced FLP degradation and meticulous thickness engineering, especially for moderately wide bandgap like GaS based devices, but also sets the stage for renewed thinking of contact integration strategy specially for large area industrial scale future developments in critically engineered next generation vdW optoelectronics. | en_US |
| dcterms.extent | xxiii, 134 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Photodiodes | en_US |
| dcterms.LCSH | Van der Waals forces | en_US |
| dcterms.LCSH | Optoelectronics | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13771