Multiple air-gap filters and constricted mesa lasers – material processing meets the front of optical device technology

Real three-dimensional material structures enable enormous perspectives in the functionality of advanced electronic and optoelectronic III/V semiconductor devices. We report on the technological implementation of surface-micromachined III/V semiconductor devices for optoelectronic applications. Considering fabrication technology, the general principles can be reduced to three fundamental process steps: deposition of a layered heterostructure on a substrate, vertical structurization and horizontal undercutting by selectively removing sacrificial layers. Very useful quality-control elements for precise process control are presented. The basic principles are applied and illustrated in detail by presenting two selected optoelectronic examples. (i) The fabrication technology of buried mushroom stripe lasers is shown. Bent waveguides on homogeneous grating fields are used to obtain chirped gratings, enabling a high potential to tailor specific performances. Excellent optical properties are obtained. (ii) The fabrication technology of vertical optical cavity based tunable single- or multi-membrane devices including air gaps is shown. Record optical tuning characteristics for vertical cavity Fabry–Pérot filters are presented. Single parametric wavelength tuning over 142 nm with an actuation voltage of only 3.2 V is demonstrated.