GaN Growth by OMVPE Techniques Using NH(3) and Novel Precursors

Graduate Student: K. Wang
Professor D. Pavlidis and Dr. C.H. Hong*
Office of Naval Research N10014-92-J1552
*Present address: Goldstar Co. Ltd.

GaN is a direct, wide bandgap semiconductor with potential applications in light emitting devices, UV emitting lasers, and high-temperature/high-power electronic devices. Ammonia (NH(3)) is most commonly used as source of the group V element for growth of III-V nitrides. This requires relatively high temperature of growth for efficient deposition. This project addresses the possibility of using phenylhydrazine ( C(6)H(5)NHNH(2) ) as an alternative source for low pressure OMVPE growth of GaN and AlN.

GaN and AlN films have been epitaxially grown on (100) Si, (100) GaAs and (0001) sapphire. The feasibility of GaN and AlN growth at low temperatures, with a mass-transport limited regime in the range of 500C to 600C, was shown. XPS and TEM were used for the analysis. GaN can be grown in either hexagonal (wurtzite) or cubic (zincblende) structure depending on the substrate symmetry and growth conditions because of the small difference in energy of formation between them. Cubic structures theoretically can possess superior electronic properties for device applications; for example, n and p type doping is known to be most efficient in all cubic III-V semiconductors whereas doping in hexagonal GaN has traditionally been recognized as being difficult. Furthermore, higher saturated electron velocities are expected due to reduced phonon scattering.

Cubic GaN epitaxial films were grown on (100) GaAs substrate by low pressure OMVPE using NH(3) as a nitrogen source. Analysis of XRD and TEM measurements show a sharp transformation from hexagonal or microtwinned cubic to cubic phase GaN grown on (100) GaAs as the growth temperature is raised from 530C to 600C. The hexagonal phase is found to dominate again as the temperature is further increased above 650C. Cubic GaN was obtained in the range of 600C to 650C. Room temperature Raman spectra show two strong peaks at 724 and 558cm^-1, which are identified as the longitudinal optical phonon and transverse optical phonon, respectively, of cubic GaN. Low temperature photoluminescence of cubic GaN has been obtained for the first time, showing a bandedge emission at 3.366eV with FWHM of 8 meV.

The Nitride studies in this project examine the nitridation influence on the epitaxially grown films, physical, electrical and optical properties of the grown layers on different substrates and control of undesirable effects limiting the background concentration and doping.

High resolution photoluminescence spectra of near band edge emission in GaN on (100) GaAs versus temperature (6.5-70K) at low excitation power (0.6 W/cm^2). The intense feature at 3.367eV has a FWHM of 5.8 meV, tracks the behavior of the bandedge and is characteristic of exciton emission.

High resolution TEM image of GaN on (111)A GaAs. The interface displays perfect crystal contact without the presence of oxide or interface layers. The configuration of the GaN atomic arrangements in this image correspond to the GaAs atomic sites of the fcc structure.

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