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Impact of thermal oxidation uniformity on 150 mm GaAs- and Ge-substrate VCSELs

Gillgrass, S. J., Allford, C. P. ORCID:, Peach, T., Baker, J., Johnson, A. D., Davies, J. I., Joel, A. M., Shutts, S. ORCID: and Smowton, P. M. ORCID: 2023. Impact of thermal oxidation uniformity on 150 mm GaAs- and Ge-substrate VCSELs. Journal of Physics D: Applied Physics 56 (15) , 154002. 10.1088/1361-6463/acc040

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Vertical cavity surface emitting laser (VCSEL) devices and arrays are increasingly important in meeting the demands of today’s wireless communication and sensing systems. Understanding the origin of non-uniform wet thermal oxidation across large-area VCSEL wafers is a crucial issue to ensure highly reliable, volume-manufactured oxide-confined VCSEL devices. As VCSEL wafer diameters approach 200 mm, germanium (Ge) is emerging as an alternative substrate solution. To this end, we investigate the uniformity of 940 nm-emitting VCSEL performance across 150 mm diameter GaAs- and Ge-substrates, comparing the oxidation method in each case. Nominally identical epitaxial structures are used to evaluate the strain induced wafer bow for each substrate type with Ge exhibiting a reduction of over 100 μm in the peak-to-valley distortion when compared with GaAs. This wafer bow is found to be the principal cause of centre-to-edge oxidation non-uniformity when utilising a conduction-heated chuck furnace, in comparison to a convection-heated tube furnace. Using on-wafer testing of threshold current, differential resistance, and emission wavelength, device performance is demonstrated for the first time across a 150 mm Ge wafer, and is shown to be comparable to performance on GaAs substrates, when the effects of oxidation uniformity are removed. These results provide evidence that there is a realistic path to manufacturing high yield VCSELs, over wafer diameters approaching those used in Si-photonics, via Ge substrates.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Additional Information: License information from Publisher: LICENSE 1: URL:, Type: cc-by
Publisher: IOP Publishing
ISSN: 0022-3727
Funders: EPSRC
Related URLs:
Date of First Compliant Deposit: 14 March 2023
Date of Acceptance: 1 March 2023
Last Modified: 20 Jun 2023 18:23

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