Optical anisotropy of ZnO nanocrystals on sapphire by thermoreflectance spectroscopy

Abstract

The band-edge excitonic transitions of vertically aligned and tilted ZnO nanorods on sapphire have been characterized using thermoreflectance (TR) measurements in the temperature range between 30 and 300 K. The TR spectra of the nanorods with largely {0001} planes show considerable difference in energy and line shape with respect to those of the other sample with largely side planes of {1010}. The TR result at each temperature clearly indicates the band-edge excitons (A, B, and C) measured from the largely {0001} planes of the rods are lower in energy with respect to those obtained from the other sample dominated by the side planes of {1010}. Optical anisotropy in the transition amplitudes of the TR spectra for the vertically aligned and tilted ZnO nanorods is observed. The TR is shown to be very sensitive to the detection of the ZnO nanorods' alignment.

Synthesis and Optical Characterization of Oxygen-Incorporated ZnS(1–x)Ox for UV–Visible Color Palette Light-Emission Matter

“…The result is caused by crystal-field and spin–orbital coupling in the valence band of the II–VI compounds. 13,28 As shown in Figure 6a, the obtained transition energies of the A, B, and C excitons of the {111}-plane ZnS, ZnS 0.94 O 0.06 , and ZnS 0.88 O 0.12 crystals are determined to be E A = 3.776, 3.751, and 3.712 eV; E B = 3.832, 3.796, and 3.771 eV; and E C = 3.917, 3.878, and 3.843 eV, respectively, at 300 K. The transition energies of ZnS, ZnS 0.94 O 0.06 , and ZnS 0.88 O 0.12 at 40 K are, respectively, E A = 3.864, 3.807, and 3.786 eV; E B = 3.918, 3.856, and 3.824 eV; and E C = 3.998, 3.943, and 3.896 eV. The energy variations of the E A , E B , and E C excitons in the ZnS (1– x ) O x series are shown by dotted arrows in Figure 6.…”

Optical anisotropy of near band-edge transitions in zinc oxide nanostructures

“…Different setting of substrate temperature may result in lower growth rate and higher sintering rate, which can change the direction of ZnO nanorods from well-aligned vertical to tilted structures during the MOCVD growth [4]. Displayed in Fig.…”

Optical Study of High Quality c -ZnS Crystals for UV Photodiodes and Photoelectrochemical Applications

“…As an environmental‐friendly wide‐bandgap semiconductor, zinc sulfide (ZnS), has recently received its increasing merits on various applications of ultraviolet (UV) optoelectronics devices, solar cells, light‐emitting diodes (LEDs) and photocatalyst owing to its wide bandgap. ZnS is direct semiconductor with a bandgap (∼3.7‐3.77 eV and exciton binding energy ∼39 meV) [2–6] larger than that of ZnO (∼3.3 eV with exciton binding energy ∼60 meV),, which makes it more suitable and flexible for application in UV‐visible optical devices. For example, for the manufacture of II–VI solid‐state lighting devices, defect emissions may play an important role in visible radiation for human eye.…”

“…The situation is similar to that of wurtzite ZnO . All the TR spectra of the {111} c ‐ZnS in Figure (a) simultaneously show three band edge transitions of E A , E B and E C detected from 30 to 300 K. The dotted lines are experimental data and solid lines are the least‐square fits to a derivative Lorentzian line‐shape function expressed as …”