Fuchun Xu

High-spatial-resolution strain measurements by Auger electron spectroscopy in epitaxial-lateral-overgrowth GaN

A high-spatial-resolution strain measurement by Auger electron spectroscopy was established and applied to analyze the strain distributions in epitaxial-lateral-overgrowth (ELO) GaN. The theoretical N KVV Auger line was set by fitting the experimental data and then the relation between Auger shift and strain was obtained. By this relation the local strain distributions in regions of special interest were measured, which well interpret the mechanism of ELO process. A crucial stage for strain release was found within a distance range above the mask. This evidence confirms the existence of the Auger physical shift.

A hierarchical lattice structure and formation mechanism of ZnO nano-tetrapods

The existence of characteristic longitudinal optical and transverse optical phonons of cubic ZnO in ZnO nano-tetrapods is determined by Raman spectroscopy and first-principles calculations. Stacking sequence change at the boundary of the core and legs is also identified by high-resolution transmission electron microscopy. Based on this experimental and theoretical evidence, we demonstrate that the lattice structure of ZnO nano-tetrapods is hierarchical with a zinc blende core connecting to four wurtzite legs. Furthermore, we establish the atomic configuration and propose a formation mechanism induced by Laplace pressure in the initial growth stage of ZnO nano-tetrapods.

Non-contact electrical detection of intrinsic local charge and internal electric field at nanointerfaces

A nanoscale non-contact electrical measurement has been developed based on Auger electron spectroscopy. This approach used the specialty of an Auger electron, which is self-generated and free from external influences, to overcome the technical limitations of conventional measurements. The detection of the intrinsic local charge and internal electric field for nanostructured materials was achieved with a resolution below 10 nm. As an example, the electrical properties at the GaN/AlGaN/GaN nanointerfaces were characterized. The concentration of the intrinsic polarization sheet charges embedded in GaN/AlGaN nanointerfacial layers were accurately detected to be -4.4 e nm(-2). The mapping of the internal electric field across the nanointerface revealed the actual energy-band configuration at the early stage of the formation of a two-dimensional electron gas.

Ideal square quantum wells achieved in AlGaN/GaN superlattices using ultrathin blocking-compensation pair

A technique for achieving square-shape quantum wells (QWs) against the intrinsic polar discontinuity and interfacial diffusion through self-compensated pair interlayers is reported. Ultrathin low-and-high % pair interlayers that have diffusion-blocking and self-compensation capacities is proposed to resist the elemental diffusion at nanointerfaces and to grow the theoretically described abrupt rectangular AlGaN/GaN superlattices by metal-organic chemical vapor deposition. Light emission efficiency in such nanostructures is effectively enhanced and the quantum-confined Stark effect could be partially suppressed. This concept could effectively improve the quality of ultrathin QWs in functional nanostructures with other semiconductors or through other growth methods.

IR transmission and reflection spectra of C 60 -doped GaAs

Three kinds of samples, C60 uniformly-doped, δ-doped and C60-Si co-doped GaAs on GaAs(001) substrates are prepared by molecular beam epitaxy. Infrared ray (IR) transmission and reflection measurements(400-4000 cm-1) have been carried out. The results show similar IR spectra between C60 uniformly-doped and δ-doped GaAs, while C60-Si co-doped GaAs display different optical properties. These phenomena are propably related to the character of C60 adsorption changing from physisorption to chemisorption via variations in surface reconstruction. C60-GaAs and C60-Si bondings may be formed in our samples. In the spectra, it is very difficult to observe direct evidence associated with C60. The C60 in GaAs may have partially decomposed.