AVS 50th International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA8
GaN Nucleation Layer Evolution on Sapphire

Tuesday, November 4, 2003, 4:20 pm, Room 321/322

Session: Compound Semiconductor Growth and Processing
Presenter: D.D. Koleske, Sandia National Laboratories
Authors: D.D. Koleske, Sandia National Laboratories
J.J. Figiel, Sandia National Laboratories
M.E. Coltrin, Sandia National Laboratories
A.A. Allerman, Sandia National Laboratories
K.C. Cross, Sandia National Laboratories
C.C. Mitchell, Sandia National Laboratories
M.J. Russell, Sandia National Laboratories
Correspondent: Click to Email
For UV, blue, green and eventually white light LEDs, GaN is most often grown on low-cost sapphire substrates. To improve the GaN epitaxial quality and reduce dislocations, a low temperature GaN nucleation layer (NL) is first deposited prior to high temperature (T) GaN growth. Despite the progress in the MOCVD growth of GaN, details of the NL and high temperature growth evolution are not well understood. In this presentation the GaN NL evolution as it is annealed from low to high T will be investigated using optical reflectance and AFM measurements of stopped growth runs. During the anneal, the NL morphology changes from a continuous 30 nm thick layer composed of 20 nm sized grains to a discontinuous layer that contains large grains approaching 500 nm in width to 180 nm in height. Further annealing of the NL causes a decrease in the size of these large grains. Since only NH@sub 3@ and H@sub 2@ are flowing during the NL annealing, the growth of the large GaN grains is explained by partial decomposition of the NL@footnote 1@ and redeposition of the Ga atoms on the growing grains through a gas phase desorption and readsorption mechanism rather than a surface diffusion mechanism. Evidence for this mechanism is obtained from the height-height correlation functions@footnote 2@ measured from the AFM images of the annealed nucleation layers as well as direct measurements of the GaN NL decomposition kinetics using optical reflectance@footnote 1@. Based on details of the decomposition kinetics and NL roughening, fits to the optical reflectance waveform will be presented. Contributions of the surface diffusion, bulk diffusion, and desorption/readsorption mechanisms to the overall GaN NL morphology will also be discussed along with guidance as to when the NL achieves optimal morphology for further GaN growth at high T. @FootnoteText@ @footnote 1@D. D. Koleske, et al., Appl. Phys. Lett 82, 1170 (2003). @footnote 2@Tong and Williams, Annu. Rev. Phys. Chem. 45, 401 (1994).