Growth of III/V on Silicon
The need to integrate an appropriate material system with Silicon to serve as an optically active region is one of the more rudimentary challenges impeding widespread adoption of integrated optoelectronics into low cost devices. While our hybrid silicon platform makes use of wafer bonding to integrate III/V and Silicon devices, and is experiencing a fair amount of success, heteroepitaxial growth of high quality III/V material on Si could potentially alleviate many of the costs and challenges involved with scaling the wafer bonding process to significantly larger wafers. Unfortunately, differences in atomic lattice constants and thermal expansion coefficients cause optically and electrically detrimental defects to form when III/V materials are grown directly on Silicon. One potential approach to eliminating these defects is epitaxial lateral overgrowth (ELO). Our research aims to optimize the quality of InP grown on a Si substrate using the ELO method in a metal organic chemical vapor deposition (MOCVD) reactor.
As shown in the illustration above, epitaxial lateral overgrowth occurs when a crystal grows selectively on regions exposed through windows patterned into a dielectric mask, which in our case is SiO2. Upon reaching the upper ledge of the mask, the crystal then begins to extend its growth laterally until neighboring growths coalesce. This has the effect of obstructing certain extended defects such as dislocations.
The slow growth rates available within MOCVD are advantageous for exploring the sequence of events during coalescence of neighboring ELO films, allowing us to optimize the coalesced film quality. Shown below are scanning electron micrographs (SEMs) and transmission electron micrographs (TEMs) showing variations in homoepitaxial ELO coalescence behavior and quality with respect to V/III precursor ratio for a mask having line openings of varying angle with respect to the [0-11] crystallographic direction. Dislocations are visible as bright lines in the TEM. These images show favorable coalescence qualities for two angle and V/III ratio pairs, being V/III=248 for lines oriented greater than 45° off of [0-11] and V/III=124 for lines oriented less than 45° off of [0-11].