Impact of strain-induced bow on the performance of VCSELs on 150mm GaAs- and Ge-substrate wafers

Baker, Jack; Gillgrass, Sara; Peach, Tomas; Allford, Craig P.; Davies, J. I.; Johnson, Andrew; Joel, Andrew M.; Lim, So Young; Shutts, Samuel; Smowton, Peter M.

doi:10.1117/12.2624492

Cited by 4 publications

(3 citation statements)

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“…The effect of wafer bow on the oxidation uniformity in GaAs B (ii) is severe enough to obscure these epitaxial nonuniformities in large diameter VCSEL wafers when using conduction heating to control process temperatures. In previous work [33], measurements on cleaved tiles, taken from different radial positions from the centre of the wafer, reported a similar decrease in oxidation extent towards the edge of the wafer.…”

Section: Oxidationsupporting

confidence: 57%

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

Gillgrass

Allford

Peach

et al. 2023

J. Phys. D: Appl. Phys.

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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.

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Section: Oxidationsupporting

confidence: 57%

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

Gillgrass

Allford

Peach

et al. 2023

J. Phys. D: Appl. Phys.

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“…Figure 4 shows the as-grown wafer surface height/distortion variation of the AlGaAs-based VCSEL structure, which was grown on a 100 mm (4-inch) GaAs substrate for this study. The small lattice mismatch between the high-Al composition n-DBR layers and the GaAs substrate results in a significant bowing of the wafer [13]. This is approximately 100 μm centre to edge for the 100 mm wafer.…”

Section: Oxidationmentioning

confidence: 99%

VCSEL quick fabrication of 894.6 nm wavelength epi‐material for miniature atomic clock applications

Baker

Allford

Gillgrass

et al. 2022

IET Optoelectronics

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A vertical cavity surface emitting laser (VCSEL) quick fabrication (VQF) process is applied to epitaxial materials designed for miniature atomic clock applications (MACs). The process is used to assess material quality and uniformity of a full 100 mm (4-inch) wafer against the stringent target specification of VCSELs for MACs. Target specifications in optical power (>0.6 mW) and differential efficiencies (<0.5 W/A) are achieved over large portions of a wafer; however, the variation in the oxide aperture diameter is shown to limit the yield. The emission of the fundamental mode at 894.6 nm at 70 ℃ is met over a significant area of the wafer for ~4 μ m aperture multi-mode devices. The consideration of the on-wafer variation reveals that further optimisation is required to increase the device yield to levels required for volume manufacture.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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“…The primary concern in the epitaxy of AlGaAs VCSELs on GaAs substrates is the inherent strain formed during VCSEL growth [6], [7]. The thickness of a typical VCSEL epitaxial structure is commonly about 5 to 15 microns, mainly contributed by the bottom and the top distributed Bragg reflectors (DBRs) made of Al x Ga 1−x As/Al y Ga 1−y As superlattices (x < y).…”

Section: Introductionmentioning

confidence: 99%

Monolithically Integrated 940 nm Half VCSELs on Bulk Ge Substrates

Zhao,

Wan,

Guo

et al. 2024

IEEE Photon. Technol. Lett.

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High-quality n-type AlGaAs distributed Bragg reflectors (DBRs) and lnGaAs multiple quantum wells (MQWs) were successfully monolithically grown on 4-inch off-cut Ge (100) wafers. Even without any design and process optimization for the Ge substrates, the Ge-based half VCSELs have photoluminescence and reflectance spectra comparable to those grown on conventional GaAs wafers. Flat and sub-nm RMS surface roughness and uniform DBR and MQW growth across the wafer were achieved. These results strongly support full VCSEL growth and fabrication on larger-area Ge wafers for the mass production of AlGaAs-based VCSELs.

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Impact of strain-induced bow on the performance of VCSELs on 150mm GaAs- and Ge-substrate wafers

Cited by 4 publications

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

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

VCSEL quick fabrication of 894.6 nm wavelength epi‐material for miniature atomic clock applications

Monolithically Integrated 940 nm Half VCSELs on Bulk Ge Substrates

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