Selective-area epitaxial growth of GaAs in deep dielectric windows using molecular beam epitaxy

An improved selective-area epitaxial growth process for GaAs in deep dielec tric windows (DDWs) is reported. The growth was carried out on (100)-orient ed semi-insulating (SI) GaAs substrate at similar to 520 degreesC by solid source molecular beam epitaxy (SSMBE) using a valved arsenic cracker source . Dielectric stacks with 10 periods of alternating silicon nitride (2000 An gstrom) and silicon dioxide (1000 Angstrom) layers were deposited using pla sma-enhanced chemical vapor deposition (PECVD) for the formation of deep (3 mum) dielectric windows. The alternating dielectric layer stack has been s hown to be of greater stability than a single dielectric layer for the purp ose of forming the DDW. A process of fabricating the DDW structures, which eliminates the possible contamination at the growth area during photoresist patterning and removing, and subsequent etching of the DDW, has resulted i n improved epitaxial layer quality. Micro-Raman spectroscopy measurements s howed a significant increase in the longitudinal-optic (LO) to transverse-o ptic (TO) signal intensity ratio (I-LO TO) from similar to4.0 to similar to 16.0 of the first-order Raman line of GaAs. Supporting evidence from low-t emperature (4 K) photoluminescence (PL) showed a reduction in intensity of the conduction band to neutral carbon acceptor (e-C degrees) emission by a factor of 4.5. This suggests lower levels of carbon contamination originati ng from the improved fabrication process of the DDW. Scanning electron micr oscopy (SEM) images showed smoother surface morphology of the GaAs inside t he DDW area. These results have important implications on the process of MB E regrowth for optoelectronics integration. (C) 2001 Elsevier Science B.V. All rights reserved.