| AVS 61st International Symposium & Exhibition | |
| Novel Trends in Synchrotron and FEL-Based Analysis Focus Topic | Monday Sessions |
| Session SA-MoM |
| Session: | Synchrotron Studies of Processes in Energy Conversion, Electronic Devices and Other Materials I |
| Presenter: | Charles Eddy, Jr., Naval Research Laboratory |
| Authors: | N. Nepal, Naval Research Laboratory M.G. Erdem, Boston University S.D. Johnson, Naval Research Laboratory V.R. Anderson, Naval Research Laboratory A. DeMasi, Boston University K.F. Ludwig, Boston University C.R. Eddy, Jr., Naval Research Laboratory |
| Correspondent: | Click to Email |
Atomic layer epitaxy (ALE) is a relatively new method to grow crystalline materials in a layer-by-layer fashion by separating the growth reaction into two surface-mediated, self-limiting half reactions at relatively low temperatures. Recently, plasma assisted ALE (PA-ALE) has been used to grow epitaxial III-nitride films at temperatures from 180-500°C [1-2]. At these growth temperatures, the ad-atom mobility is low and the growth process is highly dependent on the quality of the growth surface. Thus, understanding the mechanism of nucleation and growth kinetics is very important to improving material quality. A promising method for in situ monitoring involves the use of high intensity coherent x-rays, such as from a synchrotron light source, and includes small angle reflectance/scattering, diffraction, and fluorescence.
We present initial in situ studies of the PA-ALE process using synchrotron x-ray radiation, and grazing incidence small angle x-ray scattering (GISAXS) , x-ray reflectivity (XRR), and in-plane x-ray diffraction (XRD) measurements. Investigations focus on the in situ surface preparation process and initial stages of epitaxial growth of AlN and InN on GaN template layers. Experiments were conducted in a custom PA-ALE growth facility installed at beamline X21 of the National Synchrotron Light Source. Surface evolution during the in situ surface preparation process was monitored by GISAXS and the nucleation and growth processes for AlN and InN were monitored using GISAXS, XRR, and in-plane XRD. Atomic force microscopy (AFM), x-ray photoelectron spectroscopy and out-of-plane XRD were employed as post growth characterizations.
In situ XRR measurements of an optimized growth process for AlN on a 450°C substrate revealed a 0.08 nm/cycle growth rate and clearly shows each half-cycle of the AlN growth process. Ex situ AFM measurements confirm that the surface roughness after growth was similar (RMS roughness =0.74 nm) to that of the GaN substrate. We compare the in situ in-plane synchrotron XRD study with previous reports[2]of AlN/GaN grown in a Cambridge Nanotech Fiji reactor to assess the material quality grown in the in situ chamber. The in-plane XRD measurement on pre-grown ALE AlN confirms the epitaxial nature and wurtzite structure with 60 degree symmetry in Φ-scan. These early results demonstrate that in situ synchrotron x-ray characterization methods are a powerful tool for exploring the epitaxial nucleation and growth mechanisms of III-nitride layers by PA-ALE.
1. N. Nepal, et al., J. Cryst. Growth and Des. 13, 1485 (2013).
2. N. Nepal, et al., Appl. Phys. Lett. 103, 082110 (2013).