36 research outputs found
Bandgap and Band Offsets Determination of Semiconductor Heterostructures using Three-terminal Ballistic Carrier Spectroscopy
Utilizing three-terminal tunnel emission of ballistic electrons and holes, we
have developed a method to self-consistently measure the bandgap of
semiconductors and band discontinuities at semiconductor heterojunctions
without any prerequisite material parameter. Measurements are performed on
lattice-matched GaAs/AlxGa1-xAs and GaAs/(AlxGa1-x)0.51In0.49P single-barrier
heterostructures. The bandgaps of AlGaAs and AlGaInP are measured with a
resolution of several meV at 4.2 K. For the GaAs/AlGaAs interface, the measured
Gamma band offset ratio is 60.4:39.6 (+/-2%). For the GaAs/AlGaInP interface,
this ratio varies with the Al mole fraction and is distributed more in the
valence band. A non-monotonic Al composition dependence of the conduction band
offset at the GaAs/AlGaInP interface is observed in the indirect-gap regime.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett
The Structural Quality of AlxGa1-xN Epitaxial Layers Grown by Digitally-AlloyedModulated Precursor Epitaxy Determined by Transmission Electron Microscopy
Al(x)Ga(1-x)N layers of varying composition (0.5<x(Al)<1.0) grown in the digitally-alloyed modulated precursor epitaxial regime employing AlN and GaN binary sub-layers by metalorganic chemical vapor deposition on AlN templates were characterized by transmission electron microscopy techniques. Fine lamellae were observed in bright field images that indicate a possible variation in composition due to the modulated nature of growth. In higher Ga content samples (x(Al)<0.75), a compositional inhomogeniety associated with thicker island regions was observed, which is determined to be due to large Ga-rich areas formed at the base of the layer. Possible causes for the separation of Ga-rich material are discussed in the context of the growth regime used
Erratic Dislocations within Funnel Defects in AlN Templates for AlGaNEpitaxial Layer Growth
We report our transmission electron microscopy observations of erraticdislocation behavior within funnel-like defects in the top of AlN templates filled withAlGaN from an overlying epitaxial layer. This dislocation behavior is observed inmaterial where phase separation is also observed. Several bare AlN templates wereexamined to determine the formation mechanism of the funnels. Our results suggest that they are formed prior to epitaxial layer deposition due to the presence of impuritiesduring template re-growth. We discuss the erratic dislocation behavior in relation to thepresence of the phase-separated material and the possible effects of these defects on the optoelectronic properties
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