Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 30

In vertical‐cavity surface‐emitting lasers, the optical cavity is designed to be normal to the wafer surface, and the light emits vertically from the surface, as shown in Figure 1.2(b). High reflectivity mirrors (>99%) can be obtained with the growth of multiple epitaxial layers just above and below the active cavity without regrowth, resulting in an optical resonator cavity on the order of the emission wavelength, which is often referred to as a microcavity resonator. The lateral optical and electrical confinement is achieved by an oxidation process and may have sizes from one to several tens of microns. This lateral size controls the mode profile of the laser and will be further described in Chapter 2.

Figure 1.11 The manufacturing and testing processes of VCSELs.

Source: Figure by K. Iga and J. A. Tatum [copyright reserved by authors].

As shown in Figure 1.11, the epi‐growth process is fully monolithic and device fabrication is manufacturing‐friendly and scalable. Mass production of VCSELs thus appears more like modern LED and IC manufacturing. In contrast to FP‐edge‐emitting lasers, the handling of full wafers only (no bar handling or facet coatings), the ability of fully testing on wafer (see Appendix D), and the knowledge of yield at that point result in a lower cost for VCSELs.

Since 2020, VCSELs are manufactured on wafer diameters of 150 mm diameters and as previously described are compatible with high‐volume III–V semiconductor manufacturing processes. Many tens to hundreds of thousands of VCSELs can be fabricated on a single 150 mm wafer. With dramatic improvements in the epitaxial and fabrication processes, the device yields are routinely in excess of 90%. Details of wafer size and die counts will be given in Chapter 3. An example of fully processed VCSEL epitaxial wafer (so‐called deliverable‐wafer) is shown in Figure 1.12.

Figure 1.12 A fully processed VCSEL layer structure on 6″ (150 mm) GaAs substrate.

Source: Wafer photo by Jim A. Tatum, Dallas, Texas, USA. [copyright reserved].