High performance 940nm VCSELs on large area germanium substrates: the ideal substrate for volume manufacture

Johnson, Andrew; Joel, Andrew; Clark, Andrew; Pearce, Dan; Geen, M.W.; Wang, Wang; Pelzel, Rodney I.; Lim, So Young

doi:10.1117/12.2583207

Cited by 17 publications

(9 citation statements)

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“…This is particularly an issue for furnaces where temperature control relies on thermal contact with the heated chuck. It has been shown that VCSEL structures can be grown on Ge substrates and, owing to the elemental nature of Ge, these wafers exhibit virtually no bowing [32]. Thus, growth on Ge is promising for improving manufacturing yield of VCSELs.…”

Section: A On-wafer Vqf Performancementioning

confidence: 99%

VCSEL Quick Fabrication for Assessment of Large Diameter Epitaxial Wafers

et al. 2022

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Stripped-back representative VCSEL devices with a simple fabrication process that very closely approaches the performance of standard BCB-planarised devices have been produced. These VCSEL Quick Fabrication (VQF) devices achieve threshold currents only 0.3 mA higher than that of a standard device produced from the same material. The predictability of standard performance from VQF performance is also robustly assessed in terms of temperature effects to account for the observed disparities. These VQF devices are then processed across a 6-inch (152 mm) wafer and the resulting device-level characteristics are mapped. From this, it is apparent that there is an approximately radial decrease in oxide aperture diameter from centre to edge, found to be driven by the strain-induced wafer bow. After corrections, a residual spatial variation across the wafer remains, which, in conjunction with temperature dependent measurements, is shown to be a result of epi-material variation. By observation at 50 °C, that is, at a temperature closely resembling that of intended application, the residual centre-to-edge variation in threshold current density is found to be only 0.2 kA/cm 2 , compared to 1.3 kA/cm 2 when observing the room temperature variation of devices of nominally equivalent active volumes.

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Section: A On-wafer Vqf Performancementioning

confidence: 99%

VCSEL Quick Fabrication for Assessment of Large Diameter Epitaxial Wafers

et al. 2022

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“…Emerging applications such as autonomous things, augmented/virtual reality and automotive LiDAR demand larger arrays, higher performance, and improved reliability [3,4]. These new applications are the driving force for lower cost and increased manufacturability of VCSELs with the production of the world's first 200 mm VCSEL wafer already announced [5].…”

Section: Introductionmentioning

confidence: 99%

“…Growth of III-V layers on Ge substrates has been reported with great success recently for various applications [16,19,20]. About 980 and 940 nm emitting VCSELs have previously been demonstrated on 150 mm Ge substrates [21], with device performance at 940 nm comparable to GaAs substrate VCSELs, with fabrication completed only on small area tiles. Here, we characterise the difference in wafer bow of each substrate type and compare full 150 mm wafer-scale fabrication and device uniformity, in terms of oxide-aperture variation and performance, for nominally identical epitaxial structures grown on both GaAs and Ge substrates.…”

Section: Introductionmentioning

confidence: 99%

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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“…The market for VCSELs has been rapidly expanding for the last few years as a result of the development of 3D imaging and structured light technology, and this is predicted to continue with the application to LiDAR technology. To meet this increased demand, manufacturers have scaled their production to 6-inch substrates and are looking to go further to 8-inch in the future [1]. This requires stringent quality-control to maximise the device yield across individual wafers as well as between different wafers and different growth runs.…”

Section: Introductionmentioning

confidence: 99%