| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeM |
| Session: | Nanostructural and Surface Morphological Evolution: Experiment and Theory |
| Presenter: | Charles Eddy, Jr., U.S. Naval Research Laboratory |
| Authors: | C.R. Eddy, Jr., U.S. Naval Research Laboratory N. Nepal, U.S. Naval Research Laboratory S.G. Rosenberg, U.S. Naval Research Laboratory V.R. Anderson, Sotera Defense Solutions J.M. Woodward, U.S. Naval Research Laboratory C. Wagenbach, Boston University A.C. Kozen, U.S. Naval Research Laboratory Z.R. Robinson, College at Brockport - SUNY L.O. Nyakiti, Texas A&M University S.B. Qadri, U.S. Naval Research Laboratory M.J. Mehl, U.S. Naval Academy K.F. Ludwig, Boston University J.K. Hite, US Naval Research Laboratory |
| Correspondent: | Click to Email |
Nitride semiconductors have had significant commercial success, but full bandgap engineering of these materials is prohibited by the high temperatures used in conventional growth methods. Recently, we have developed a growth method –low temperature atomic layer epitaxy (ALEp) – that has empirically produced crystalline semiconductor films with properties comparable to those from conventional growth processes, but at roughly half the growth temperature [1,2]. This has eliminated miscibility gaps in ternary III-N semiconductor films and enabled the realization of full bandgap engineering from 0.7 eV to 6.1 eV.
Despite these empirical successes, the fundamental mechanisms involved in ALEp are unknown and the full promise of the method unrealized. To obtain such enabling knowledge we have employed synchrotron-based grazing incidence small angle x-ray scattering (GISAXS) to study the low temperature atomic level processing (ALP) of GaN substrate surfaces for epitaxy and ALEp nucleation and growth of InN on said surfaces. GISAXS allows real-time, in situ monitoring of the surface morphology during these processes.
In this presentation, we will introduce the GISAXS method and the apparatus we have developed to conduct in situ GISAXS measurements of the aforementioned ALP and ALEp processes. We monitor the evolution of GaN substrate surface morphology during a series of low-temperature ALPs including: gallium flash off (GFO), hydrogen plasma clean, and nitrogen plasma nitridation. We learn that the optimum surface results from a GFO conducted at 500° C for only 10 cycles followed by a hydrogen plasma clean. Further, we learn that conventional plasma nitridations are detrimental to smooth surface evolution. When employed to study ALEp InN nucleation and growth, GISAXS data, coupled with Porod[3] and 2D Fourier Transform analysis, affords a clear picture that the growth proceeds by island nucleation and growth and not by the conventionally accepted layer-by-layer growth associated with atomic layer deposition. We have monitored the evolution of island nucleation density, island spacing, island shape and island size as a function of key ALEp growth parameters. We observe that the islands are generally tens of nm or less in size and evolve from a spherical mound shape to a cylindrical shape. Finally, we will present the variations between 2D and 3D growth modes with growth parameter variations that provide insights on process modifications to promote higher quality electronic materials growth.
1. Nepal et al., Cryst. Growth and Des., 13, 1485 (2013)
2. Nepal et al., Thin Solid Films 589, 47 (2015).
G. Porod, Kolloid Z., 124, 83 (1951).