15 January 2008 Understanding GaN nucleation layer evolution on sapphire and its impact on GaN dislocation density
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Abstract
For improved GaN films on sapphire, GaN nucleation layers (NLs) are typically grown prior to high temperature growth. Using optical reflectance and AFM image analysis we have uncovered mechanistic details of GaN NL evolution during the ramp to high temperature. As the temperature is increased the NL decomposes and GaN nuclei form. We will demonstrate that the GaN nuclei are formed from gas phase Ga atoms generated during the NL decomposition which recombine with ambient NH3. Continued GaN growth on these nuclei results in GaN films with dislocation densities as low as 4x108 cm-2. We will show how the NL decomposition kinetics can be extracted from the optical reflectance waveforms and used to control the nuclei formation and growth. More recently we have investigated possible correlations between the GaN nucleation density and the resultant film dislocation density. We have initiated studies of ultra-low (< 107 cm-2) nucleation densities on sapphire using multi-step NL growth and annealing schemes. We find that over a wide range of nucleation densities that the nucleation density scales quadratically with the NL thickness. The dependence of the dislocation density on the nucleation density is currently being explored.
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Daniel D. Koleske, Daniel D. Koleske, Michael E. Coltrin, Michael E. Coltrin, Stephen R. Lee, Stephen R. Lee, Gerald Thaler, Gerald Thaler, Karen C. Cross, Karen C. Cross, Michael J. Russell, Michael J. Russell, } "Understanding GaN nucleation layer evolution on sapphire and its impact on GaN dislocation density", Proc. SPIE 6841, Solid State Lighting and Solar Energy Technologies, 68410H (15 January 2008); doi: 10.1117/12.758766; https://doi.org/10.1117/12.758766
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