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Influences of the Composition on Spectroscopic Characteristics of Al$_x$Ga$_{1-x}$N Thin Films
New Phys.: Sae Mulli 2018; 68: 1281~1287
Published online December 31, 2018;
© 2018 New Physics: Sae Mulli.

Dae Jung KIM1, Bong Jin KIM1, Duk Hyeon KIM1, Jong Won LEE*2

1 School of Basic Sciences, Hanbat National University, Daejeon 34158, Korea
2 Department of Advaned Materials Engineering, Hanbat National University, Daejeon 34158, Korea
Correspondence to:
Received September 7, 2018; Revised October 16, 2018; Accepted October 30, 2018.
cc This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
In this study, Al$_x$Ga$_{1-x}$N films were grown on (0001) sapphire substrates by using metal-organic chemical vapor deposition (MOCVD). The crystallinity of the grown films was examined with X-ray diffraction (XRD) patterns. The surfaces and the chemical properties of the Al$_x$Ga$_{1-x}$N films were investigated using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The optical properties of the Al$_x$Ga$_{1-x}$N film were studied in a wide photon energy range between 2.0 $\sim$ 8.7 eV by using spectroscopic ellipsometry (SE) at room temperature. The data obtained by using SE were analyzed to find the critical points of the pseudodielectric function spectra, <$\varepsilon(E)$> = <$\varepsilon_1(E)$> + $i$<$\varepsilon_2(E)$>. In addition, the second derivative spectra, $d^2$<$\varepsilon(E)$>/$dE^2$, of the pseudodielectric function for the Al$_x$Ga$_{1-x}$N films were numerically calculated to determine the critical points (CPs), such as the $E_0$, $E_1$, and $E_2$ structure. For the four samples ($x$ = 0.18, 0.21, 0.25, 0.29) between a composition of $x$ = 0.18 and $x$ = 0.29, changes in the critical points (blue-shifts) with increasing Al composition at 300 K for the Al$_x$Ga$_{1-x}$N film were observed via ellipsometric measurements for the first time.
PACS numbers: 3.20.At, 78.20.Ci
Keywords: Al$_x$Ga$_{1-x}$N film, Spectroscopic ellipsometry, Metal-organic chemical vapor deposition, Pseudodielectric function, Atomic force microscopy, X-ray photoelectron spectroscopy

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