Philips VCSEL Technology
The structure and function of a Vertical Cavity Surface Emitting Laser (VCSEL) is illustrated by the figure on the right. It shows a combination of a Scanning Electron Microscope picture of the cross section of a single VCSEL, with a schematic diagram of the vertical structure.
VCSELs are semiconductor laser-diodes, which emit light (1) perpendicular to the surface. The laser consists of active layers, with a thickness of a few nm. In these layers, the electrical carriers are converted into light. Above and below the active layer, multiple layers of alternating refractive index form resonant mirrors (4). The short laser cavity requires a high reflectivity of the mirrors in order to achieve sufficient gain. The doped semiconductor mirrors additionally provide electrical contacts (2) and (3) to the active layers. The size of the active area is defined by the width of an oxidized layer (6) near the active layer.
The layer structure and the vertical light emission allow producing fully functional lasers in a single growth step. After this epitaxial growth process, standard semiconductor wafer processing steps define the emission area and provide electrical terminals to the individual laser-diodes.
The vertical structure of the VCSEL allows building a large number of lasers next to each other to form 2D arrays. Depending on the application, the VCSELs in these arrays can be electrically connected either individually (by individual contacts for e.g. multi-channel datacom applications), or in parallel. In the parallel arrangement of a large number of lasers, the current is provided to the individual lasers by a thick conductor layer (5), to provide low resistance electrical terminals to the arrays.