High-frequency and below bandgap anisotropic dielectric constants in α-(AlxGa1−x)2O3 (≤x≤1)

Abstract

A Mueller matrix spectroscopic ellipsometry approach was used to investigate the anisotropic dielectric constants of corundum α-(AlxGa1−x)2O3 thin films in their below bandgap spectral regions. The sample set was epitaxially grown using plasma-assisted molecular beam epitaxy on m-plane sapphire. The spectroscopic ellipsometry measurements were performed at multiple azimuthal angles to resolve the uniaxial dielectric properties. A Cauchy dispersion model was applied, and high-frequency dielectric constants are determined for polarization perpendicular (ε∞,⊥) and parallel (ε∞,∥) to the thin film c-axis. The optical birefringence is negative throughout the composition range, and the overall index of refraction substantially decreases upon incorporation of Al. We find small bowing parameters of the high-frequency dielectric constants with b⊥=0.386 and b∥=0.307.

Determination of anisotropic optical properties of MOCVD grown m-plane α-(Al x Ga1−x )2O3 alloys

“…The trend of the dielectric limit as a function of Al content x is displayed in Fig. 7 (red and green circles) and compared to results of Hilfiker et al 51) (black and gray triangles) and their corresponding bowing fit (black and gray dashed lines).…”

Electrical and Structural Properties of Two-Inch Diameter (0001) α-Ga2O3 Films Doped with Sn and Grown by Halide Epitaxy

“…The phase composition was determined from Ɵ−2Ɵ X-ray diffraction scans, while the crystalline quality was assessed by measurement of the Full Width at Half-Maximum (FWHM) of highresolution, triple-axis symmetric and asymmetric rocking curves. The X-ray reflections used were (0006) and (10)(11)(12)(13)(14)(15)(16)(17)(18). The details can be found in our earlier papers.…”

“…Detailed descriptions of experimental setup can be found in our earlier papers. [35][36][37][38][39][40][41] Results and Discussion XRD measurements of the half of the two-inch grown film showed that it is single-phase α-Ga 2 O 3 , with the FWHM of the symmetric (0006) reflection varying between 13 arcminutes and 15 arcminutes, and the FWHM of the asymmetric (10)(11)(12)(13)(14)(15)(16)(17)(18) asymmetric reflection between 14 and 17 arc. minutes.…”

“…[1][2][3][4] This emerging semiconductor is a potential next frontier material, especially for hightemperature and radiation hard applications. The advantages to using the α-Ga 2 O 3 polymorph come from a higher bandgap than for β-Ga 2 O 3 (5.2 eV vs 4.9 eV), higher symmetry (corundum vs monoclinic) and hence lower impact of anisotropy, the existence of a host of related oxides with transition and rare metals allowing fabrication of useful heterojunctions [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] and the possibility of solving, at least in principle, of the very acute problem of the lack of feasible p-type doping in all Ga 2 O 3 polymorphs. 29 The device potential of α-Ga 2 O 3 has been demonstrated by several groups.…”

Al Composition Dependence of Band Offsets for SiO2 on α-(AlxGa1−x)2O3

“…1 The α-polytype is a potential solution to extending the stability to higher Al contents and higher temperatures. [2][3][4][5][6][7][8][9][10][11][12] This metastable, corundum crystal structure α-polytype, transforms to the β-polymorph at temperatures above 750 °C-900 °C under equilibrium conditions. 5 Of all reported polymorphs, this phase has the highest optical bandgap with energies ranging between 5.0 eV and 5.3 eV for the binary.…”