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Quick fabrication VCSELs for characterisation of epitaxial material

Baker, Jack, Allford, Craig P. ORCID:, Gillgrass, Sara-Jayne, Forrest, Richard, Hayes, David G. ORCID:, Nabialek, Josie, Hentschel, Curtis, Davies, J. Iwan, Shutts, Samuel ORCID: and Smowton, Peter M. ORCID: 2021. Quick fabrication VCSELs for characterisation of epitaxial material. Applied Sciences 11 (20) , 9369. 10.3390/app11209369

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A systematic analysis of the performance of VCSELs, fabricated with a decreasing number of structural elements, is used to assess the complexity of fabrication (and therefore time) required to obtain sufficient information on epitaxial wafer suitability. Initially, sub-mA threshold current VCSEL devices are produced on AlGaAs-based material, designed for 940 nm emission, using processing methods widely employed in industry. From there, stripped-back Quick Fabrication (QF) devices, based on a bridge-mesa design, are fabricated and this negates the need for benzocyclcobutane (BCB) planarisation. Devices are produced with three variations on the QF design, to characterise the impact on laser performance from removing time-consuming process steps, including wet thermal oxidation and mechanical lapping used to reduce substrate thickness. An increase in threshold current of 1.5 mA for oxidised QF devices, relative to the standard VCSELs, and a further increase of 1.9 mA for unoxidised QF devices are observed, which is a result of leakage current. The tuning of the emission wavelength with current increases by ~0.1 nm/mA for a VCSEL with a 16 μm diameter mesa when the substrate is unlapped, which is ascribed to the increased thermal resistance. Generally, relative to the standard VCSELs, the QF methods employed do not significantly impact the threshold lasing wavelength and the differences in mean wavelengths of the device types that are observed are attributed to variation in cavity resonance with spatial position across the wafer, as determined by photovoltage spectroscopy measurements.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Additional Information: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (
Publisher: MDPI
ISSN: 2076-3417
Funders: UKRI, EPSRC, IQE plc
Date of First Compliant Deposit: 12 October 2021
Date of Acceptance: 7 October 2021
Last Modified: 06 Jan 2024 04:12

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