Formation behavior of BexZn1−xO alloys grown by plasma-assisted molecular beam epitaxy

Abstract

We report the phase formation behavior of BexZn1−xO alloys grown by plasma-assisted molecular beam epitaxy. We find the alloy with low- and high-Be contents could be obtained by alloying BeO into ZnO films. X-ray diffraction measurements shows the c lattice constant value shrinks, and room temperature absorption shows the energy band-gap widens after Be incorporated. However, the alloy with intermediate Be composition are unstable and segregated into low- and high-Be contents BeZnO alloys. We demonstrate the phase segregation of BexZn1−xO alloys with intermediate Be composition resulted from large internal strain induced by large lattice mismatch between BeO and ZnO.

Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory

“…In addition, experimental studies of BeZnO for a wide range of compositions are challenging because of phase segregation observed for the solid solutions with both low (more than $10% Be) and high Be (less than $75% Be) content. 8 In regard to bandgap bowing, we obtain relatively large BeZnO bowing of 6.94 eV and relatively small MgZnO bowing of 0.237 eV, which shows that the bowing parameters increase with the size difference of the constituents. Shi and Duan 42 calculated bandgaps of zinc blende BeMgZnO using LDA to DFT and reported large and composition dependent bandgap bowing parameters.…”

“…As MgO is stable in the rocksalt phase (7.7 eV bandgap), phase segregation in MgZnO is inevitable and has been reported for Mg concentrations above 33% (corresponding wurtzite MgZnO bandgap of $4.0 eV) for films grown at substrate temperatures of !600 C. 3,4 Higher Mg contents up to 55% (corresponding wurtzite MgZnO bandgap of $4.5 eV) could be achieved at much lower growth temperatures of 250 C at the expense of significantly degraded material quality and tendency toward phase segregation at elevated temperatures. 5 On the other hand, in the case of BeZnO ternary (BeO having the wurtzite structure with 10.6 eV bandgap), the phase segregation is primarily driven by the large difference in covalent radii (1.22 Å for Zn and 0.96 Å for Be 6 ) and has been observed for Be contents as low as 10%, [7][8][9] despite the relatively low growth temperatures used (400-500 C).…”

Understanding the origin of phase segregation of nano-crystalline in a BexZn1−xO random alloy: a novel phase of Be1/3Zn2/3O

“…Among these ZnO-based alloys, the Mg x Zn 1−x O alloy has been widely investigated, [5][6][7][8][9][10][11][12][13] since its band gap can be tuned from 3.37 eV (for wurtzite ZnO) to 7.8 eV (for rocksalt MgO). [20][21][22] More recently, the recrystallization of the Be x Zn 1−x O alloy under thermal treatment has been found to significantly influence the electronic and optical properties of the BeZnO based devices. 36.…”

Temperature-dependent structural relaxation of BeZnO alloys

“…Be x Zn 1Àx O alloy films with x range from 0 to 1 have been already prepared by some research groups, which the band-gap of Be x Zn 1Àx O alloy can be tuned from 3.37 eV (ZnO) to10.6 eV (BeO). 8,9 Ryu et al also fabricated a ZnObased UV LED with BeZnO/ZnO quantum wells as the active layer. The exciton binding energy in the active layer is exceptionally large (263 meV), which allows the fabrication of high efficiency LEDs or LDs.…”