Richard Moug

Structural Properties and Spatial Ordering in Multilayered ZnMgTe/ZnSe type-II Quantum Dot Structures

We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in th...

Determination of excitonic size with sub-nanometer precision via excitonic Aharonov-Bohm effect in type-II quantum dots

A spectral analysis of the Aharonov-Bohm (AB) oscillation in magneto-photoluminescence intensity was performed for stacked type-II ZnTe/ZnSe quantum dots (QDs). Very narrow AB oscillations (∼0.3 T) allowed for probing of both the lateral size distribution in the stack ensemble of QDs and the size of type-II excitons as determined by the electronic orbit with sub-nanometer precision. Two sets of stacks with excitonic size of 18.2 and 17.5 nm are determined to be present in the sample.

Growth and stability of zinc blende MgS on GaAs, GaP, and InP substrates

The molecular beam epitaxial growth of zinc blende (ZB) MgS on GaAs, GaP, and InP substrates has been investigated by X-ray diffraction and RHEED, with MgS layer strain varying between 3.1% compressive strain (GaP) and 4.4% tensile strain (InP). ZB MgS could be grown on all three substrates. X-ray diffraction showed substantial MgS relaxation during growth before conversion to the rock salt phase. Results are compared with predictions that stable growth on GaP is unlikely and relaxed ZB MgS does not grow in layers over a few A thick. Our results imply growth of ZB MgS is truly metastable.

Epitaxial lift-off of II–VI semiconductors from III–V substrates using a MgS release layer

Epitaxial lift-off (ELO) is a post-growth process that allows an epitaxial layer to be removed from its original substrate and transferred to a new one. ELO has previously been successfully demonstrated for III–V materials and also ZnSe based II–VI semiconductors using a MgS sacrificial layer. Following the recent successful growth of epitaxial MgS layers on GaP and InP substrates, in this paper we compare ELO of II–VI epilayers grown on GaP, GaAs, and InP substrates using MgS sacrificial layers in the range of 7–15 nm thick. Good quality lifted layers are obtained rapidly from InP and GaAs substrates. For GaP substrates, ELO is much slower and good quality lifts have only been achieved with ZnSe epilayers. Photoluminescence spectra obtained from epitaxial layers before and after ELO show changes in peak positions, which are compatible with changes of strain in the layer. The layers produced by ELO are flat and free of cracks, suggesting that this is an efficient and convenient method for the transfer of ...

Surface plasmon resonance (SPR) in a chemically etched ZnSe substrate and its effect on the Raman signal enhancement

We report the observation of surface-enhanced Raman scattering (SERS) from a chemically etched ZnSe surface using 4-mercaptopyridine (4-MPy) as probe molecules. A thin film of ZnSe is grown by molecular beam epitaxy (MBE) and then etched using a strong acid. Protrusions of hemi-ellipsoidal nanoparticles are observed on the surface. Using the results of the Mie theory, we controlled the size of the nanoparticles to overlap significantly with maximum efficiency of near-field plasmon enhancement. In the Raman spectrum, we observe large enhancements of the a1, b1, and b2 modes when 4-MPy molecules are adsorbed on the surface using a 514.5 nm laser for excitation, indicating strong charge-transfer contributions. An enhancement factor of (2×106) is observed comparable to that of silver nanoparticles. We believe this large enhancement factor is an indication of the coupled contribution of several resonances. We propose that some combination of surface plasmon, charge transfer, band gap resonances are most likely the contributing factors in the observed Raman signal enhancement, since all three of these resonances lie close to the excitation wavelength.