Page 352 - Introduction to Information Optics

6.5. Integration of Vertical Cavity Surface-Emitting Lasers (VCSELs) 337

(a) (b)

Fig. 6.35. (a) SEM picture of a section of a linear thin-film VCSEL array with 12 elements, (b)
Mechanically polished VCSELs (substrate thickness ~42/im, and emitting aperture 15/un).

is pictorially shown in Fig. 6.36. The epitaxial liftoff method has the advantages
of reproducibility and mass productivity. To adapt the epitaxial liftoff method,
VCSEL devices should be fabricated on the top of the AlAs sacrificial layer,
which is located between the bottom DBR and the GaAs substrate.

Epitaxial liftoff process for VCSELs (with reference to Fig. 6.36)
1. Etch a donut-shaped 2-fim mesa using wet etchant. It defines oxidizing
regions to confine current. In the next step, lateral oxidization in a
furnace (465°C, water vapor introduced) is performed until the desired
laser aperture is reached (15/mi diameter).

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Fig. 6.36. Epitaxial lift-off process for VCSEL integration.