The group III nitrides are wide band-gap semiconductors that have demonstrated considerable promise for various optoelectronic, high-temperature and high-power device applications. The development of GaN epitaxy on Si substrates would decrease substrate cost compared to sapphire and SiC and would allow integration with existing Si processing technology.
A technique was developed to deposit single crystal GaN on Si (111) directly using an oxynitride SiOxN1-x compliant interface to relieve stress at the substrate-film interface. A thermodynamic assessment of the Ga-N-O-Si system was performed using the ThermoCalc software package to understand the chemistry at the Si/GaN interface. An equilibrium phase-diagram was generated. It was shown experimentally that low-temperature growth prevented the formation of the detrimental Si3N4, phase. Our direct process uses 2 steps: a thin MOCVD layer followed by a HVPE growth in the same reactor. A capping GaN layer was grown in an alternate reactor that is a traditional low-pressure cold-wall MOVPE system. Crack-free, single-crystal GaN have been demonstrated using the sequence of a low temperature MOCVD layer (560oC) followed by a HVPE GaN layer (560 to 900oC). Single crystal GaN was demonstrated by MOCVD even at a growth temperature of 900^oC. Additional parameters such as growth temperature, V/III ratio, III/Cl ratio, substrate preparation and pre-treatment were optimized to provide the best crystalline quality as judged by XRD, TEM and SEM.
We have investigated the use of GaN, AlN and ZnO buffer layers on the quality of GaN films grown on Si(111) and Si(100) substrates.
Different characterization techniques, such as PL, ESCA, SIMS, AES were used for films and substrates characterizations.