Mechanisms of dislocation reduction in GaN using an intermediate temperature interlayer Page: 4 of 12
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7.8 pmole/min and the molar ratio of V/III precursors was 50. The differences between
growth of GaN using dimethylhydrazine and growth of GaN using ammonia have been
previously reported 15. About 600 nm to 1000 nm of GaN was deposited at 1000 C (first
high temperature layer). The growth rate was about 1lpm/hr. The temperature was then
rapidly ramped down to an intermediate temperature (700 to 900 C) for growth of the
intermediate temperature-interlayer (IT-IL) and growth was allowed to proceed at this
temperature for 15 minutes. The temperature was then rapidly ramped back up to
10000C to grow the top high temperature GaN layer.
RESULTS AND DISCUSSION
Using laser reflectance we determined the transition temperature at which the
growth mode changes from a three-dimensional mode (3D) to a two dimensional mode
(2D) ". A 3D growth mode results in the roughening of the surface which results in a
decrease of the reflectance of the layer. A 2D growth mode smooths the surface and the
reflectance increases to its maximum value that can be calculated theoretically 16. With
our growth conditions 2D growth occurs above about 995 C. When the temperature is
suddenly decreased to yield a 3D growth mode, with a low flow of reactants, a low
density of small islands is nucleated on the growing surface. We found that at lower
temperatures (below 900 C) the islands are Ga-rich. At 800 C, these islands are
randomly distributed, not uniform in sizes and have a metallic, rounded appearance when
observed by optical microscopy. These islands then convert to GaN islands with a
distinctive pyramidal shape during the temperature increase back to 10000C at which
temperature a 2D growth mode is reestablished and growth of the islands progresses
mostly laterally. The dislocations propagate in the growth direction and therefore bend
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Bourret-Courchesne, E.D.; Yu, K.M.; Benamara, M.; Liliental-Weber, Z. & Washburn, J. Mechanisms of dislocation reduction in GaN using an intermediate temperature interlayer, article, April 2, 2001; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc715407/m1/4/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.