Zhou-jun Wang

Simultaneous N-intercalation and N-doping of epitaxial graphene on 6H-SiC(0001) through thermal reactions with ammonia

AbstractSurface functionalization of epitaxial graphene overlayers on 6H-SiC(0001) has been attempted through thermal reactions in NH3. X-ray photoelectron spectroscopy and micro-region low energy electron diffraction results show that a significant amount of N is present at the NH3-treated graphene surface, which results in strong band bending at the SiC surface as well as decoupling of the graphene overlayers from the substrate. The majority of the surface N species can be removed by annealing in vacuum up to 850 °C, weakening the surface band bending and resuming the strong coupling of graphene with the SiC surface. The desorbed N atoms can be attributed to the intercalated species between graphene and SiC. Low temperature scanning tunneling spectroscopy and density functional theory simulations confirm the presence of N dopants in the graphene lattice, which are in the form of graphitic substitution and can be stable above 850 °C. This is the first report of simultaneous N intercalation and N doping of epitaxial graphene overlayers on SiC, and it may be employed to alter the surface physical and chemical properties of epitaxial graphene overlayers.

Photoluminescence of InAs quantum dots grown on GaAs surface

InAs quantum dots (QDs) grown on GaAs surface are investigated. The observed abnormal photoluminescence (PL) properties, including extremely sharp high-energy peaks, almost temperature-independent linewidth, and fast thermal quenching, are discussed in terms of the strong quantum confinement effects due to the absence of a cap layer and the lack of carrier redistribution channel caused by the small number of QDs capable of contributing to PL and the high-density surface defects

Graphene as a surfactant for metal growth on solid surfaces: Fe on graphene/SiC(0001)

X-ray photoelectron spectroscopic and scanning tunneling microscopic results demonstrate that annealing of Fe/carbon-rich 6H-SiC(0001) surface between 650 and 750 °C leads to Fe intercalation under the surface carbon layer. Accompanied with the metal intercalation, the carbon nanomesh surface was transformed into a graphene surface. Moreover, the formed graphene layers always float out to the topmost surface even after deposition of more than 10 monolayer Fe, acting as a surfactant. Using graphene as the surfactant may not only promote the 2D growth but also can improve the film performance considering that graphene is stable and robust.

Photoluminescence of rapid-thermal annealed Mg-doped GaN films

We report investigation of temperature and excitation power dependencies in photoluminescence spectroscopy measured from Mg-doped GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition. The objective is to examine the effects of rapid-thermal annealing on Mg related emissions. It is observed that the peak position of the 2.7/spl sim/2.8 eV emission line is a function of the device temperature and detailed annealing procedure. The phenomenon is attributed to Coulomb-potential fluctuations in the conduction and valence bandedges and impurity levels due to the Mg-related complex dissociation. The blue shifts of the 2.7/spl sim/2.8 eV emission lines with increasing excitation power provides clear evidence that donor-acceptor recombination process underlies the observed emission spectrum.