Research Experiences for Undergraduates
Materials Research at Carnegie Mellon University
Robert F. Davis
Bertucci
Distinguished Professor
Department
of Materials Science and Engineering
Carnegie
Mellon University
“Initial and Subsequent Modes
of Growth of
AlN, GaN and ZnO Semiconductor Thin Films”
Wednesday, August 1, 2007
12 PM Seminar in Wean Hall 5310
Refreshments will be served.
The initial and subsequent stages of growth of AlN
on 4H-SiC( ),
GaN on AlN(0001),  )
and sapphire as well as ZnO on GaN(0001), GaN( )
and other substrates will be discussed and illustrated. The
results acquired from atomic force and various electron
microscopies as well as x-ray photoelectron spectroscopy
will be integrated with the lecture. It will
be shown that AlN nucleates and grows on 4H-SiC( )
via the Stranski-Krastanov mode with the eventual formation
of densely packed, [0001]-oriented individual islands. Additional
deposition results in the gradual reorientation of
the growth microstructure along the [ ]. By
contrast GaN nucleates and grows on AlN( )
via the Volmer-Weber mode with rapid growth of islands
along the [ ]
to near surface coverage at a thickness of 2 nm. Continued
deposition results in both faster vertical growth along
[ ]
relative to the lateral growth along [0001] and a [ ]-oriented
microstructure containing rows of GaN. Fully
dense GaN films develop between 100 and 250 nm of growth,
and the preferred in-plane orientation changes to [0001]. GaN(0001)
and ZnO(0001) films have a strong preference for growth
along [ ]
and [0001], respectively. The latter nucleate
via the Volmer-Weber mode on GaN(0001). Continued
growth occurs as [0001]-oriented needles even on ZnO
substrates. Limitations on growth and doping
and the incorporation of impurities during growth will
also be discussed. |
