Frequency shifts of the E2high Raman mode due to residual stress in epitaxial ZnO thin films

Abstract

To investigate the stress effect on the E2high Raman vibration mode, we grew heteroepitaxial ZnO films on c-plane sapphire with different strain states by changing the film thicknesses between 5 and 100 nm. To determine the relationship between the observed frequency of the E2high mode with the biaxial residual stress of the ZnO thin films, the out-of-plane strain of films were measured with x-ray diffraction from which the residual stress was calculated. The biaxial residual stress and E2high frequency were related linearly by a factor of ∼170 MPa/cm−1, which is in agreement with reported values from high pressure investigations of bulk ZnO.

Comparative Study of ZnO Thin Films Grown on Quartz Glass and Sapphire (001) Substrates by Means of Magnetron Sputtering and High-Temperature Annealing

“…where, σ and ∆ω are the residual stress and the shift compared with the standard E 2 (high) mode of the stress-free ZnO bulk [4,26], respectively. The E 2 (high) mode of the stress-free ZnO bulk is located at 437 cm −1 .…”

“…Semiconductor materials play a critical role in modern society and have been made into light emitting diodes (LEDs) [1][2][3], surface acoustic wave (SAW) devices [4], sensors [5][6][7][8], solar cells [9], and so on [4,[10][11][12], which significantly promote our life quality. ZnO is an enduring star of the third-generation semiconductor materials owing to its unique merits.…”

“…First of all, ZnO is non-toxic and of perfect biocompatibility, leading to the great potential applications of biodetectors and biomedical restorative materials [13]. Furthermore, the electrical properties of ZnO can be improved by doping with other elements, and ZnO has been widely applied in LEDs [1,2], laser diodes [4], SAW devices [4], etc. ZnO is of low cost, and Al-doped ZnO is of excellent conductivity as well as cheap, which is considered a superior substitute for the expensive indium tin oxide (ITO) transparent conductive material [14][15][16].…”

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

“…Gd-doped ZnO films decreases, the phonon mode E 2 (high) peak shifts toward higher frequencies. The possible mechanisms that can be responsible for such a shift are (i) the biaxial strain, 48 (ii) phonon localization, 49,50 and (iii) laserinduced heating in materials and tensile strain during Raman measurements. 49,50 As E 2 (high) peak is expected to shift to the higher frequency value as the compressive biaxial stress increases (and c-parameter value decreases), we assume the unusual shift of E 2 (high) peak to lower frequencies as c-parameter decreases in our samples can be due the second assumption, which is phonon localization by defects, such as those related to oxygen deficiency, 51 zinc excess or surface impurities, are in line with the PL and XRD measurements, suggesting that defects related to oxygen deficiency such as V O accompanied Gd dopants.…”

Microstructure, optical properties, and catalytic performance of Cu2O-modified ZnO nanorods prepared by electrodeposition

“…Raman and PL spectra analysis Figure 6 shows the Raman and PL spectra of Cu 2 Omodified ZnO nanorods with Cu 2 O deposition for 0 and 5 min. The peak at 437 cm −1 is due to the E 2 high vibration mode of ZnO hexagonal crystal structure as shown in Figure 6a [41]. Figure 6a also shows that the stronger Raman peak of 218 cm −1 , which corresponds to 2Γ 12− vibration modes of Cu 2 O.…”