Oxide-confined VCSELs fabricated with a simple self-aligned process flow

Abstract : We propose a simplified and easier fabrication process flow for the manufacturing of AlOx-confined VCSELs based on combining the oxidation step with a self-aligned process, allowing the mesa etching and two successive lift-off steps based on a single lithography step. The electro-optical confinement achieved by standard lateral oxidation enables a low threshold and a single mode behaviour for the VCSEL. This simplified process can largely improve VCSEL manufacturing by reducing the processing time and costs compared to the standard VCSEL process. Introduction: Vertical-cavity surface-emitting lasers (VCSEL) have become the preferred light sources in many photonic systems, enabling short-link interconnections [1] but also in other emerging mass-market applications like sensing and detection [2]. The large production volume of VCSELs would benefit from a simplification of the manufacturing process flow that may largely increase the cost-effectiveness. Indeed, compared to the LED and LDs, the VCSEL fabrication process flow requires a large number of elementary steps defined by successive inter-aligned photolithography levels. A precision in the micron range is required to ensure the lateral alignment between the optical waveguide and the electrical injection. For these reasons, one of the most important concerns for the VCSEL manufacturers is to improve the production throughput by lowering the fabrication time and cost per wafer. The development of a self-aligned process is of great interest as already demonstrated for the fabrication of high performance HBT transistors or ridge lasers [3,4]. To that extent, Al-Omari [5] used a top metallic contact deposited over a photoresist layer as a hard mask to dry-etch the VCSEL mesa. Chua [6] developed a pseudo-planar approach by opening via holes down to the AlAs layer to carry out the lateral oxidation. This process has subsequently been improved by Strzelecka [7] to increase the device density. Recently, we have shown that air-post VCSELs could be created using an innovative self-aligned process, which combined several masking and lift-off steps defined by a single lithographic step [8]. In this paper, we extend this work and propose a new process flow to fabricate, in a very simple and straightforward way, the widely-used oxide-confined VCSELs. The demonstrated process drastically simplifies the oxide-confined VCSEL fabrication by reducing the total number of lithographic alignment steps from four or more to only one alignment, with the additional advantage of relieving the required tolerances. This process flow, most suitable for 3D imaging and sensing applications, can also be easily implemented for the fabrication of other optoelectronic devices such as modulators, ridge waveguide lasers, detectors, solar cells or any process combining dry etch, passivation and metallization.
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Semiconductor Science and Technology, IOP Publishing, 2017, 32 (12), pp.125004. 〈10.1088/1361-6641/aa90ae〉
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Ludovic Marigo-Lombart, Stéphane Calvez, Alexandre Arnoult, Hugo Thienpont, Krassimir Panajotov, et al.. Oxide-confined VCSELs fabricated with a simple self-aligned process flow. Semiconductor Science and Technology, IOP Publishing, 2017, 32 (12), pp.125004. 〈10.1088/1361-6641/aa90ae〉. 〈hal-01614784〉

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