| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Charles Eddy, Jr., U.S. Naval Research Laboratory, USA |
| Authors: | N. Nepal, U.S. Naval Research Laboratory, USA V.R. Anderson, U.S. Naval Research Laboratory, USA S.D. Johnson, U.S. Naval Research Laboratory, USA D.J. Meyer, U.S. Naval Research Laboratory, USA B.P. Downey, U.S. Naval Research Laboratory, USA Z.R. Robinson, The College at Brockport SUNY, USA K.F. Ludwig, Boston University, USA C.R. Eddy, Jr., U.S. Naval Research Laboratory, USA |
| Correspondent: | Click to Email |
A challenge to the development of III-N semiconductors (AlN, GaN and InN and their ternaries and quaternaries) is the requisite heteroepitaxy on foreign substrates, compounded by increasing device structure complexity. To address ternary layer miscibility gaps, substrate versatility and low strain heterojunctions the growth temperature must be reduced. Recently, plasma assisted atomic layer epitaxy (PA-ALE) has been used to grow InN and In containing ternaries at temperatures ≤ 260 °C [1-2]. At these growth temperatures, ad-atom mobility is low and understanding the mechanism of nucleation and growth is critical for improved material quality. Traditional ultra-high vacuum in situ monitoring methods are impractical as the growth pressure for PA-ALE is too high (1-500 mTorr). High intensity coherent x-rays, such as from a synchrotron light source, offer an effective alternative to study PA-ALE nucleation and growth process.
Here we present in situ studies of the effect of nitrogen plasma pulse time on temporal evolution of the growth surface for InN growth on a-plane sapphire at 250 °C as revealed by real-time grazing incidence small angle x-ray scattering (GISAXS) measurements. Ex situ atomic force microscopy, x-ray photoelectron spectroscopy and reflectivity, and Hall measurements were employed to characterize the resulting films.
GISAXS measurements show that H2 plasma cleaning roughens the substrate surface, but this same surface is recovered during subsequent N2 plasma treatment. During the initial cycles of growth the diffuse specular reflection broadens and correlated peaks (CPs) evolve along the native wing with different correlated length scales (CLSs). For a nitrogen plasma pulse time (tp) of 15 seconds, CPs have two different CLSs of 33.36 and 8.38 nm. With increasing tp to ≥ 20s, a single CP evolves and the longest CLS of 11.22 nm is for tp = 25s. Additionally at tp = 25s, the growth rate is largest (0.035nm/cycle – consistent with self-limited growth [1]) with root mean square surface roughness and carbon impurity at or below instrument sensitivity limits. Thus the nature of GISAXS CP CLS directly correlate with the material quality. For the tp = 25s film, 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, which is higher than the reported value of 30 cm2/V-s for a 1300 nm thick InN grown by molecular beam epitaxy directly on sapphire [3].
[1] Nepal et al., Cryst. Growth and Des. 13, 1485 (2013).
[2] Nepal et al., Thin Solid Films 589, 47 (2015).
[3] Kuo et al., Diamond & Related Materials 20, 1188 (2011).