The standard method for growth rate determination in semiconductor thin films, by Molecular Beam Epitaxy (MBE), is through RHEED intensity oscillations prior to device layer epitaxy. High quality III-Nitride epitaxy occurs with metal-rich surfaces and under step-flow growth conditions, which do not produce RHEED oscillations. This article demonstrates the capability to monitor the growth rate of gallium nitride (GaN), at any point during film growth with high fidelity, under step-flow growth conditions. RHEED intensity vs. time measurements determine the growth rate by Metal Modulated Epitaxy (MME). Utilizing differential analysis, a factor of 2x improvement in accuracy is demonstrated, with a Standard Error less than 4%. Complementary analysis with X-Ray Diffraction and RHEED identify the Ga bilayer thickness as 2.34 ML +/- 0.08 ML, representing the first time RHEED analysis has been used to characterize the thickness of the Ga bilayer on GaN.

GaAs nanostructures were grown on patterned GaAs (111) B substrates with molecular beam epitaxy. Nanopatterns were achieved by patterning a thin film of silicon dioxide (SiO2) grown on the substrate surface with a self-organized porous alumina template. Growth of patterned nanostructures took place through the holes in the SiO2 film. The authors obtained two kinds of nanostructures: nanopillars and nanodots. The majority of nanopillars had two kinds of tops, i.e., hexagonal flat top and pyramidal top, as observed with a scanning electron microscope. High resolution transmission electron microscopy studies showed epitaxial relationships between the nanostructures and the substrates. Photoluminescence measurements of nanopillars showed the photoluminescence peak shifted to a higher energy compared to films grown under the same condition.

The supplemental material provides both experimental and theoretical details, including SEM, TEM, and XRD patterns and some references. All chemicals were used as received without further purification. Titanium (TTIP) was used as the titanium source. Trioctylphosphine (TOP) and urea were chosen as precursors for the phosphorus and nitrogen doping. Both urea and NH 3 have been used as N sources for TiO 2 doping in earlier studies 1,2. Urea is chosen in this work due to its ease of handling and its environmental-friendly nature. The choice of P source is another key factor

We demonstrate experimentally a chemical codoping approach that would simultaneously narrow the band gap and control the band edge positions of TiO2 semiconductors. It is shown that a sequential doping scheme with nitrogen (N) leading the way, followed by phosphorus (P), is crucial for the incorporation of both N and P into the anion sites. Various characterization techniques confirm the formation of the N-P bonds, and as a consequence of chemical codoping, the band gap of TiO2 is reduced from 3.2 eV to 1.8 eV. The realization of chemical codoping could be an important step forward in improving the general performance of electronic and optoelectronic materials and devices.

This investigation focuses on the formation of nanoscale puddles of an intermediate metallic phase (IMP) in the metal-insulator transition (MIT) temperature regime of single-crystalline vanadium dioxide (VO2) nanowires. The electronic structure of VO2 nanowires was examined with scanning tunneling spectroscopy. The evolution of the local density of states of individual nanowires throughout the MIT regime is presented with differential tunneling conductance spectra and images measured as the temperature was increased. Our results show that the formation of an IMP plays an important role in the MIT of intrinsic VO2.

We demonstrate experimentally a chemical codoping approach that would simultaneously narrow the band gap and control the band edge positions of oxide semiconductors. Using TiO2 as an example, we show that a sequential doping scheme with nitrogen (N) leading the way, followed by phosphorous (P), is crucial for the incorporation of both N and P into the anion sites. Various characterization techniques confirm the formation of the N-P bonds, and as a consequence of the chemical codoping, the band gap of the TiO2 is reduced from 3.0 eV to 1.8 eV. The realization of chemical codoping could be an important step forward in improving the general performance of electronic and optoelectronic materials and devices.

We report studies of two key factors involved in the use of MnAs as a spin injector, namely, Mn diffusion and spin injection properties when it is grown on GaAs-based semiconductor heterostructures. Depth profile of Mn concentration in a sample consisting of a MnAs film grown on GaAs is investigated with time-of-flight secondary ion mass spectroscopy. The result shows that Mn diffusion into GaAs is negligible, unlike the case of Ga 1− x Mn x As/GaAs, in which Mn diffusion is significant. Meanwhile, robust spin injection is observed with MnAs as a spin injector for a GaAs-based light emitting diode, persisting up to room temperature.