Saturation and beating of acoustic phonon oscillations excited near the exciton resonance of strained polar ZnO/Zn_0.8Mg_0.2O multiple quantum wells

Abstract

Coherent acoustic phonons and carrier dynamics in ZnO/Zn0.8Mg0.2O multiple quantum wells from the perturbation of the built-in electric field are investigated using a degenerate pump–probe measurement technique near the exciton resonance.

Exciton Localization of High-Quality ZnO/MgxZn1–xO Multiple Quantum Wells on Si (111) with a Y2O3 Buffer Layer

“…The blue shift of the PL emission is attributed to the screening of the internal electric field by high densities of electron−hole dipoles, which are known as QCSE screening. 5,29 Different from the power-dependent PL spectra of ZnO/ZnMgO MQWs, the ZnO buffer layer exhibits the monotonic red shift and broadening of the UV peak with increasing excitation power, which is due to a stronger local heating effect. 30 For understanding the varying of exciton binding energy and exciton−phonon coupling strength under the quantum confinement effect, Figure S4a−c illustrate the temperaturedependent PL spectra of ZnO/ZnMgO MQWs with L w = 1.6, 2.7, and 5.6 nm, respectively, taken from 10 to 300 K. With the increasing the temperature from 10 K to RT, the PL peaks of all 3 samples exhibit some degree of S-curve dependence of NBE peak with temperature, implying that the MQWs have localized potential wells induced by the local variation in well width or inhomogeneity of alloy potential in the MgZnO barrier layers.…”

“…To minimize the effect of magnesium diffusion into the well layers by thermal driving force at high growth temperature, we adopted temperature-gradient control, in which the growth temperature of the barriers was set lower than that of the well layers. 5 1a. XRD measurements were performed with a nine-circle diffractometer at the IU22 undulator beamline TPS-09A of Taiwan Photon Source and beamline BL13A at the National Synchrotron Radiation Research Center with an incident wavelength of 1.0331 Å.…”

“…In these studies, ScAlMgO 4 or sapphire are the extensively used substrates for the growth of ZnO/ZnMgO MQWs. 4,5 Although many MQWs researches on the structural and optical properties using sapphire, ScAlMgO 4 , ZnO substrates, 4−6 etc., were conducted by many groups, there are few literatures about the structural and optical properties of MQWs grown on Si, especially for high quality ZnO/ Mg x Zn 1−x O multiple quantum wells. Because of the merits of the low cost, excellent quality, and large-area availability of Si wafer, the unique opportunity of integrating well-established Si electronics with ZnO-based optoelectronic devices, the direct growth of high-quality epitaxial ZnO film on Si is highly desired.…”

“…Therefore, much effort has been devoted toward the investigation and fabrication of ZnO/ZnMgO MQWs for UV light emitter applications. In these studies, ScAlMgO 4 or sapphire are the extensively used substrates for the growth of ZnO/ZnMgO MQWs. , …”

All optical control of comb-like coherent acoustic phonons in multiple quantum well structures through double-pump-pulse pump-probe experiments

“…For example, the adjustment of pump light wavelength can result in the phonon pulse shape variation due to the altering of optical absorption spectra in a triple-quantum-well structure [25]. The optical pump power influence on the CAPs amplitude in a ZnO/ZnMgO MQWs structure, induced by the variation of photo-excited carriers and the screening effect, was also examined [26]. On the basis of the ultrafast optical single-pulse coherent control of CAP via optical pulse parameter modifications, the multiple-pulse optical manipulation of CAPs has arisen increasing attention and attained noticeable progress, which enables selective excitation in superlattices [27,28], MQW structures [29,30], nanoparticles [31], plasmonic nanostructures [32] and aluminum gratings [33], frequency tuneabilities in single quantum well structures [34] and thin films [35], and phase shifts in a MQW structure [36].…”