Bum-Joon Kim

Realization of High-Power Highly Efficient GaInP/AlGaInP Ridge Laser Diodes for Recordable/Rewritable Digital Versatile Discs

Very efficient and reliable GaInP/AlGaInP red multiple-quantum-well laser diodes for recordable/rewritable digital versatile disc (DVD-R/RW) were successfully developed by low-damage fabrication. Because we adopted dry etching instead of conventional chemical wet etching for the steep ridge sidewalls of laser diodes (LDs), devices could be operated at a high output power over 200 mW at 70°C without showing any unstable higher-order transverse modes. In-situ monitoring tools in metal organic chemical vapor deposition (MOCVD) and dry etching were useful for controlling process parameters precisely, which enhances device characteristics and maintains the reproducibility of device fabrication. A very small beam aspect ratio of 1.78 with a very low vertical beam divergence angle of 15.3° at a high output power was achieved by optimizing the two-step n-cladding layer in our LD structures. These low values of the vertical beam divergence angle and aspect ratio are essential for minimizing the coupling loss between the LD and the objective lens in DVD pickups.

Formation of vertical ridge structure in 660nm laser diodes for high power single mode operation

We report a method for formation of a ridge with almost vertical sidewalls in the fabrication of ridge stripe AlGaInP laser diode structures, which cannot be easily achieved when a conventional wet-etch process is used, for high power operation with a fundamental transverse mode. By depositing additional oxides protecting layers on the sidewalls after the dry-etch process, a wet-etch process, which is necessary to remove the plasma-induced damaged portion of the etched region, can be safely applied and the vertical ridge shape maintained. Using this method, the ideally rectangular ridges were obtained and the single mode operation of 660nm laser diode with up to 270mW output power was successfully achieved.

Estimating the Optical Thickness Errors in Vertical-Cavity Surface-Emitting Laser Structures from Optical Reflection Spectra

Effects of the systematic epi-layer thickness errors on the optical reflection spectra have been studied in epitaxial wafers for 850 nm vertical-cavity surface-emitting lasers (VCSELs), and a procedure of estimating the error layer and magnitude is proposed. The experimentally confirmed procedure is based on the finding that the overall shape of the reflection spectra depends mainly on a newly defined parameter, the effective error.