| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+AS+NS+SA-ThM |
| Session: | Thin Film: Growth and Characterization, Optical and Synchrotron Characterization I |
| Presenter: | Neeraj Nepal, U.S. Naval Research Laboratory |
| Authors: | N. Nepal, U.S. Naval Research Laboratory V. Anderson, U.S. Naval Research Laboratory S.D. Johnson, U.S. Naval Research Laboratory B. Downey, U.S. Naval Research Laboratory D. Meyer, U.S. Naval Research Laboratory A. DeMasi, Boston University K.F. Ludwig, Boston University C. Eddy, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
Atomic layer epitaxy (ALE) is a layer-by-layer materials growth method. Recently, plasma enhanced ALE (PA-ALE) has been used to grow epitaxial III-nitride films at temperatures ≤500°C [1-2]. At these growth temperatures, the ad-atom mobility is low and the growth process is significantly influenced by the nature of the substrate surface. Thus, the mechanisms of nucleation and growth kinetics is very important to understand to improve material quality for technological applications. Synchrotron x-ray characterization is one of the best methods for this study.
The temporal evolution of high quality InN growth on a-plane sapphire at 200-250°C were probed by synchrotron x-rays. The growth was carried out in a thin film growth facility installed at beamline X21 of the National Synchrotron Light Source at Brookhaven National Laboratory and at Cornell High Energy Synchrotron Source, Cornell University. Real-time grazing incidence small angle x-ray scattering (GISAXS) measurements at the x-ray incidence angle of 0.8 degrees show that H2 plasma cleaning roughens the sapphire substrate surface, but this same surface is recovered completely during subsequent N2 plasma pretreatment. GISAXS also reveals InN growth steps for each PA-ALE cycle at the optimal growth conditions. During the initial cycles the specular peak broadens and the Yoneda Wing (YW) scattering has a correlated length scale (CLS) of 17.4 nm indicating roughening of the surface during homogenous nucleation. At about 1.3 nm of growth the intensity of YW is increased at the CLS of 10.1 nm indicating a decrease in the surface roughening CLS. Despite this scattering, ex situ atomic force microscopy-measured roughness is below instrument sensitivity limits, demonstrating the effectiveness of GISAXS compared to more conventional approaches. In situ x-ray reflectivity measurements suggest that the InN growth was self-limited with a growth rate of 0.35 nm/cycle between 200-250°C. Hall measurements show electron sheet carrier density and resistance of 3.5x1013 cm-2 and 3.59 kW/sq, respectively. An electron mobility of 50 cm2/V-s is measured for a 5.6 nm thick InN film on a-plane sapphire, which is higher than the reported value of 30 cm2/V-s for a 1300 nm thick InN grown by MBE directly on sapphire [3]. In situ synchrotron x-ray study of the epitaxial growth kinetics of InN films is one of the most powerful methods to understand nucleation and growth mechanisms to improve material quality and broaden material applications.
References:
[1] Nepal et al., Cryst. Growth and Des. 13, 1485 (2013).
[2] Nepal et al., Appl. Phys. Lett. 103, 082110 (2013).
[3] Kuo et al., Diamond & Related Materials 20, 1188 (2011).