Semiconductor lasers, which convert electrical current into optical radiation, have operating conditions in the kilo-ampere and mega-watt per square centimeter range. Scaling the chip dimensions and confining electrical and optical paths have enabled a large range of practical applications like reading and writing information in CD-, DVD- and Blue-Ray equipment, as well as source- and pump lasers for optical fiber telecommunication systems.
The buried heterostructure (BH) for InP-based lasers is very popular due to its attractive properties resulting from the electrical and optical confinement in the active stripe, completely embedded in InP material. BH-lasers have the advantage of low threshold and operating currents, continuous-wave operation at high temperatures, stable fundamental lateral optical modes, good control of optical output beams for efficient output coupling, as well as having excellent RF properties for high speed applications.
Ever since the mid-eighties of last century SMART Photonics and its predecessors have spent a tremendous amount of manpower in optimizing the BH production process. The delicate process steps of mesa etching, wafer cleaning prior to selective epitaxial re-growth, heating procedure, growth initiation, MOCVD re-growth and post epitaxial wafer processing were optimized for high performance BH lasers with a high reliability. Depending on the specific requirements, either a p-n-p current blocking, followed by local removal of this structure reducing the capacitance for high speed applications, or a high resistivity layer can be grown on both sides of the mesa.