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Quick VCSELs and wafer assessment for volume MOVPE production

Baker, Jack 2023. Quick VCSELs and wafer assessment for volume MOVPE production. PhD Thesis, Cardiff University.
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The development of a Quick VCSEL (QuickSEL) process as a fast, efficient, and reliable quality control method in production settings is presented. Devices are fabricated within 24 hours and produce output characteristics which are comparable to that of standard planarised structures, intended for use in rapid prototyping of epitaxial designs and for the assessment of epi-wafer quality and uniformity in volume settings. From post-growth material characterisation and wafer-scale device-level testing, the quality and uniformity of generic MOVPE-grown 6-inch GaAs substrate VCSEL wafers is assessed. Variation of the oxide aperture across wafers processed whole is shown to have a significant effect on the uniformity of device performance. Even when accounted for, some residual variation in device performance remains, which is attributed to the variation in the properties of the epi-layers, specifically, a spatially varying detuning of the gain peak and cavity resonance wavelengths, and mirror reflectivity. The first in-depth comparative experimental study on the performance of 940 nm VCSELs on GaAs and Ge substrates is also presented. Parity in performance between GaAs and Ge substrate VCSELs in terms of key figures of merit is demonstrated. The thermal resistance is measured to be within error despite a smaller oxide aperture and thicker substrate of the Ge VCSELs under test. It is concluded that potential enhancements are to be found in the thermal performance of VCSELs on Ge. The advantage of improved oxidation uniformity associated with the reduced wafer bow of large diameter Ge wafers is demonstrated. The variation of the material properties represented by the photoluminescence and Fabry-Perot cavity resonance wavelengths are found to be equivalent, showing that radial variations which are generally observed are not driven by wafer curvature. This study demonstrates that high-performance epitaxial structures can be grown on Ge substrates with wafer-scale uniformities equivalent to that of structures grown on GaAs.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: VCSEL, MOVPE, volume, production, performance, uniformity, yield, GaAs, Ge, wafer
Funders: EPSRC
Date of First Compliant Deposit: 6 February 2024
Last Modified: 06 Feb 2024 13:23

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