Orientation-Mediated Luminescence Enhancement and Spin-Orbit Coupling in ZnO Single Crystals

Abstract

Temperature-, excitation wavelength-, and excitation power-dependent photoluminescence (PL) spectroscopy have been utilized to investigate the orientation-modulated near band edge emission (NBE) and deep level emission (DLE) of ZnO single crystals (SCs). The near-band-edge emission of ZnO SC with <0001> orientation exhibits strong and sharp emission intensity with suppressed deep level defects (mostly caused by oxygen vacancies Vo). Furthermore, Raman analysis reveals that <0001> orientation has dominant E2 (high) and E2 (low) modes, indicating that this direction has better crystallinity. At low temperature, the neutral donor-to-bound exciton (DoX) transition dominates, regardless of the orientation, according to the temperature-dependent PL spectra. Moreover, free-exciton (FX) transition emerges at higher temperatures in all orientations. The PL intensity dependence on the excitation power has been described in terms of power-law (I~Lα). Our results demonstrate that the α for <0001>, <1120>, and <1010> is (1.148), (1.180), and (1.184) respectively. In short, the comprehensive PL analysis suggests that DoX transitions are dominant in the NBE region, whereas oxygen vacancies (Vo) are the dominant deep levels in ZnO. In addition, the <0001> orientation contains fewer Vo-related defects with intense excitonic emission in the near band edge region than other counterparts, even at high temperature (~543 K). These results indicate that <0001> growth direction is favorable for fabricating ZnO-based highly efficient optoelectronic devices.

Crucial roles of structural, morphological, and optical properties in enhancing the photocatalytic performance of ZnO nanorods

“…Figure 6 displays the photoluminescence (PL) spectra of ZnO nanorod samples obtained at different hydrothermal reaction temperatures. To enhance the observation of transitions from deep-level energy states, an excitation wavelength of 405 nm was utilized, as shorter excitation wavelengths often overlook these transitions [42]. Within the visible emission range, the emissions primarily originate from deep-level defects, with green emissions (490 nm to 570 nm) and yellow emissions (570 nm to 590 nm) being the most prevalent.…”

Editorial for the Special Issue “Applications of Optical Thin Films”

“…High-sensitivity SERS substrates, which contain several-nanometer-thickness silver and are easily fabricated using DC magnetron sputtering, were studied by Wu et al [2]. Spin-orbit-coupled ZnO single crystals with enhanced orientation-mediated luminescence were developed by Hassan et al [3], and Su et al [4] developed a Cr/n-Si Schottky junction for use in mid-infrared technology. A germanium (Ge) thin film grown using low-temperature plasma-enhanced chemical vapor deposition was developed by Lin et al [5] to mode lock an erbium-doped fiber laser in order to generate a 1600 nm IR light.…”