Hexagonal prism blue laser diode using whispering gallery mode resonances toward reduced threshold power.

摘要

Semiconductor laser diodes have properties favored in various applications, such as optical storage and phase modulation based communication systems, where LEDs are not applicable. However, the relatively high threshold power has been a major obstacle to energy-efficient UV/blue semiconductor laser diodes as the high threshold power contributes to high power consumption and device instability due to Joule heating. Of the factors that influence the threshold power, the geometry of the optical cavity and the quality of the facets are among the most important.;Instead of concentrating on improvements in materials quality, this study investigated a unique cavity geometry that promises to yield reductions in threshold power. Unlike current commercial semiconductor laser diodes with rectangular (∼ 400x100 microns) cavities that use longitudinal one-dimensional resonances, the hexagonal prism cavity allows total internal reflection (TIR) and whispering gallery mode (WGM) resonances that yield higher quality factors compared to rectangular-shaped cavities.;Hexagonal prism cavity diodes fabricated by reactive ion etching showed a continuous wave (cw) resonant peak at 481 nm at room temperature with 7 nm full-width-at-half-maximum (FWHM), compared to a FWHM of 23 nm for conventional LEDs fabricated from the same heterostructure. Although the resonant peak width is wider than that of current laser diodes, the observed threshold current density and voltage were 3.7kA/cm2 and 8.41V, respectively, which correspond to one of the lowest threshold powers reported to date. Another approach for further threshold power reduction was pursued by growing atomically flat and high-quality facets using selective epitaxial growth (SEG). The potential for fabricating hexagonal prism cavity lasers by SEG is discussed.