Lattice Parameter Variation in ScGaN Alloy Thin Films on MgO(001) Grown by RF Plasma Molecular Beam Epitaxy
- PDF / 680,892 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 181 Views
1202-I05-25
Lattice Parameter Variation in ScGaN Alloy Thin Films on MgO(001) Grown by RF Plasma Molecular Beam Epitaxy Costel Constantin1, Jeongihm Pak2, Kangkang Wang2, Abhijit Chinchore2, Meng Shi2, and Arthur R. Smith2 1
Department of Physics, Seton Hall University, South Orange, NJ 07079 2 Nanoscale & Quantum Phenomena Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 ABSTRACT We present the structural and surface characterization of the alloy formation of scandium gallium nitride ScxGa1-xN(001)/MgO(001) grown by radio-frequency molecular beam epitaxy over the Sc range of x = 0-100%. In-plane diffraction measurements show a clear face-centered cubic surface structure with single-crystalline epitaxial type of growth mode for all x; a diffuse/distinct transition in the surface structure occurs at near x = 0.5. This is consistent with out-of-plane diffraction measurements which show a linear variation of perpendicular lattice constant a⊥ for x = 0 to 0.5, after which a⊥ becomes approximately constant. The x = 0.5 transition is interpreted as being related to the cross-over from zinc-blende to rock-salt structure. INTRODUCTION The technological achievement of light emitting diodes (LEDs) made out of wurtzite GaN (w-GaN) spurred much interest in related III-nitrides such as aluminium nitride (AlN) and and indium nitride (InN). Wurtzite GaN has a band gap of 3.4 eV and emits invisible, highly energetic ultraviolet light, but when some of the gallium atoms are substituted by indium atoms, highly efficient violet, or blue LEDs can be obtained. However, alloying w-GaN with AlN or InN has shown a decrease in device efficiency as the emission wavelength is shifted towards the near infrared-end of the visible spectrum. A very good alternate to w-GaN is the cubic GaN (cGaN) which has several interesting properties such as a direct wide band gap of EDc − GaN = 3.2 eV , a tetrahedral zinc-blende bonding structure with a lattice constant of ac-GaN = 0.452 nm [1, 2]. On the other hand, scandium nitride (ScN) is a semiconductor with a direct band gap of ScN EDScN = 2.15 eV and a lower indirect band gap of E I = 0.9 eV [3-7]. The most stable crystal structure of ScN observed experimentally so far is the rock-salt structure with a relaxed lattice constant aScN = 0.4501 nm [6]. It can be noticed that there is ~ 0.2 % lattice constant mismatch between c-GaN and ScN, and also the different bandgaps [i.e., c-GaN (3.2 eV), and ScN (2.15 eV)] makes ScGaN alloying and the growth of c-GaN/ScN and ScN/c-GaN extremely appealing. We previously reported the growth of ScxGa1-xN on wurtzite GaN, and we found that for both low x and high x, alloy-type behavior is observed. For x ≥ 0.54, rock-salt structure is found; for small x up to 0.17, an anisotropic expansion of the ScGaN lattice is observed which is interpreted in terms of local lattice distortions of the wurtzite structure in the vicinity of ScGa substitutional sites in which there is a decrease of the N-Sc-N bond angle. This tendency toward flattening of
Data Loading...
