Chemical Cleaning of Gratings in Distributed Feedback InP Lasers

Abstract

We have studied three chemical solutions for cleaning gratings prior to InP epitaxial growth for distributed feedback laser applications. These chemicals are concentrated H2SO4 and mixed solutions of nH2SO4--H~O2--H20 where n = 5 and 10. On InP substrates, the etching rate of H2SO4--H202--H20 solutions was about 2-3 times faster than that of concentrated H2SO4. The H2SO4--H202--H20 s~lutions etched the grating structure isotropically and preserved the original grating morphology. However, H2SO4 tended to remove the sharp ridges of the original grating and reduce the distributed feedback effect. We have also found that the H2SO4--H20~--H20 solutions are much more effective than H2SO4 in removing carbon contaminants, which could provide nucleation sites for dislocation loops and adversely affect the laser diodes' reliability.Recently, considerable interest has been devoted to distributed feedback (DFB) lasers because of their stable emission wavelength and narrow spectral linewidth. These performance attributes are important to a n u m b e r of optical fiber communication applications such as high bit rate, long-haul fiber links, wavelength multiplexing, and coherent communication systems. The fabrication of DFB lasers involves three major steps: (i) grating fabrication, (ii) wafer cleaning, and (iii) overgrowth of hetero-

Investigation of masking materials for high-ion-density plasma etching of GaAs

“…Mask degradation generates a number of undesirable characteristics in etched features, including defects on the active layer, sloped sidewalls, lift-off of the mask and sidewall roughening of the active layer [3,4]. In those problems, transfer of sidewall roughness from the mask into the semiconductor can be a significant disadvantage in making a device for waveguide or laser devices because of the reduction of optical efficiency by scattering losses of light from the facets [5][6][7].…”