A unified process for fabricating lasers, detectors, modulators, and waveguides

A unified process for integrating lasers, detectors, modulators, and waveguides for optoelectronic integrated circuits (OEICs) on a single substrate is described. The devices are fabricated from a quantum well heterostructure (QWH). Initial efforts have been directed toward fabricating these devices in a ridge waveguide form because of the simplicity of fabrication. A QWH is grown by metalorganic chemical vapor deposition (MOCVD) and modified as necessary to produce detectors, modulators, and waveguides. The detector is essentially given, because the laser structure can be operated with no bias (no dark current) and photogenerated carriers will be swept out of the quantum well by the large built-in field. The waveguides are produced by etching a ridge to induce an effective lateral index step, as are the other devices, and the GaAs quantum well can also be slightly disordered using Ga vacancy diffusion to shift the absorption edge of the waveguide to a longer wavelength than the emission wavelength of the laser. The modulator regions may be Ga vacancy diffused or not, depending on the modulator type and function. The characteristics of an inline laser-modulator-detector structure are reviewed. Results of modeling ridge waveguide structures for Δβ modulators are discussed. Several self-aligned fabrication processes that have the best prospects for reliable integration of lasers, detectors, modulators, and waveguides are introduced