Abstract

Various fabrication methods for semiconductor waveguides have already been proposed. Recently,¹ localized vapor phase epitaxy (LOCVPE) (a chloride process) was found to be an attractive alternative solution to the conventional etching-based techniques (rib or ridge waveguides). Losses of 1 dB/cm in GaAs have been measured, the LOCVPE process has been further developed, and new structures have been made on both GaAs and InP. Figure 1 illustrates three possible waveguide structures. In Fig. 1(a) an external waveguide is fabricated by epitaxial growth through a stripe opening in a dielectric overlayer. The waveguide’s cross section depends on the growth conditions but is, in all cases, limited by perfect crystallographic planes. Using a similar dielectric overlayer and performing an in situ high-temperature (720°C) chemical etching (HCI) prior to growth, an embedded waveguide can be obtained [Fig. 1(b)]. Figure 1(c) illustrates the case when a V-groove is made on a substrate which is not covered with the dielectric film, the VPE anisotropy being then adjusted to obtain a perfectly planarized waveguide structure. For all these structures, the main advantage of LOCVPE is to grow extremely smooth facets and thus to reduce the losses from scattered light. The measured losses are dominated by the free electron absorption of the substrate. The importance of this absorption for various waveguide structures as well as doping of the substrate will be discussed.

© 1986 Optical Society of America