Biexciton emission from high-quality ZnO films grown on epitaxial GaN by plasma-assisted molecular-beam epitaxy

Abstract

We have investigated the optical and structural properties of high-quality ZnO films grown on epitaxial GaN (epi-GaN) by plasma-assisted molecular-beam epitaxy employing low-temperature buffer layers. High-resolution x-ray diffraction for both symmetric and asymmetric reflexes shows that crystalline defects in ZnO films have a similarity to epi-GaN used as a substrate. The quality of ZnO epilayers grown on epi-GaN is basically determined by epi-GaN. The photoluminescence (PL) spectrum at 10 K exhibits very sharp exciton emission with a linewidth of 1.5 meV, while deep-level emission is negligible, indicative of small residual strain. At 77 K, PL is dominated by a free-exciton emission line in the low-excitation regime, while it is overtaken by a new emission band due to biexcitons at its low-energy side as the excitation intensity increases. This biexciton emission band emerges even under the intermediate excitation regime of 100 W/cm2, which is 100 times smaller than the previously reported threshold for bulk ZnO. The biexciton binding energy is estimated to be 15 meV, in agreement with previous results. At the higher excitation regime, the emission line due to exciton–exciton scattering dominates the PL spectrum.

Characterization of nanostructured ZnO thin films deposited through vacuum evaporation

“…A wide range of techniques to deposit thin films are used, such as molecular beam epitaxy (MBE) [5], single-source chemical vapor deposition (SS CVD) [6], metalorganic chemical vapor deposition (MOCVD) [7], sol–gel [8], spray pyrolysis [9], and RF magnetron sputtering [10]. However, the vacuum evaporation technique is used to deposit worm-form nanostructured thin films.…”

RF Power and Thermal Annealing Effect on the Properties of Zinc Oxide Films Prepared by Radio Frequency Magnetron Sputtering

“…Numerous techniques [4][5][6][7][8][9] have successfully been used to synthesize ZnO films. Effects of sputtering variables on ZnO film properties have been some of the major research topics.…”

Growth mechanism of ZnO low-temperature homoepitaxy

“…PL is known to be strongly influenced by the structural defects, which cause radiative or nonradiative transitions. 25,33 Especially, excitonic emission lines and their linewidth are sensitive to crystalline quality. 25,33 These mean that the welldefined excitonic emission features and the very sharp emission peaks of sample III are ascribed to the high-crystal quality, while the weak emission intensity and the broad emission spectra of samples I and II are ascribed to the defective material properties.…”

“…25,33 Especially, excitonic emission lines and their linewidth are sensitive to crystalline quality. 25,33 These mean that the welldefined excitonic emission features and the very sharp emission peaks of sample III are ascribed to the high-crystal quality, while the weak emission intensity and the broad emission spectra of samples I and II are ascribed to the defective material properties. Then, the emission linewidths of D o X in samples I, II, and III were estimated to be 19, 7.8, and 2.4 meV, respectively.…”