Novel heterostructure designs for surface emitting light sources.

Abstract

Novel heterostructures in compound semiconductor light emitting devices have been investigated in order to study their impact on device performance. Specifically, three types of active regions have been designed for application to surface emitting lasers and LEDs. Such schemes are shown to promote enhanced device performance and possibilities for future applications in flat panel displays and optical communication systems. A new type of vertical cavity surface emitting laser is proposed and analyzed to show the possibility of optical pumping from an integrated edge-emitting laser. With this scheme it may be possible to make VCSELs of very small dimensions and VCSEL arrays. The laser design utilizes etching and epitaxial regrowth of quantum wells to provide different gain regions for the surface and edge-emitting sections. The multi-mode rate equations are used to evaluate the possibility of such a laser and the roles of the various design parameters are discussed. It is seen that efficient surface photon emission is possible for high vertical cavity mirror reflectivities and sufficient separation of bandgap energies for the two quantum well gain regions. Another type of novel heterostructure design was studied in staggered type II GaP/AlGaP quantum wells. A sharp no-phonon peak observed in the photoluminescence (PL) spectra of these heterostructures is believed to originate from considerable overlap of the carrier wavefunctions and Gamma-X bandmixing. In addition to the sharp no-phonon transition in the green (556 nm), observation was made of a dominant broad emission in the ultraviolet (UV) region of the spectrum (363 nm). Light emitting diodes fabricated with similar heterostructures exhibited significant green emission at room temperature. Finally, the oxide-confined surface emitting laser has come of interest since the discovery of controlled wet-oxidation of AlAs. Such lasers have surpassed the minimum limits in threshold currents and devices diameters of proton-implanted VCSELs. Thus, high-speed characterization of these lasers in relation to their multi-transverse modes is of interest for low power and high-speed applications. The multiple resonance peaks seen in the modulation response of these lasers exhibit strong correlation to the multi-transverse optical modes existing as a result of spatial hole burning and device heating. These correlations may allow multi-mode optical links to be designed for higher-speeds and greater distances than previously imagined.