Optoelectrical properties of highly mismatched semiconductor materials

Dilute nitride alloys of III–V semiconductors, and transparent conducting group-II oxides may both be categorised as highly mismatched compounds. The small size and high values of electronegativity of nitrogen and oxygen (see figure), compared to the substituted anion, in dilute nitrides, and the cation, in transparent conducting oxides, give rise to striking properties in these materials. The dilute nitride alloys GaNSb, InNSb, and GaInNSb, grown by molecular beam epitaxy, have been studied. Infrared absorption measurements of GaNSb are presented, showing the divergence of transitions from the valence band to E− and E+ conduction bands with increasing nitrogen incorporation. The fitting of the positions of the valence band to E+ transitions gives a value of 2.6 eV for the coupling parameter in this material. A reduction in the bandgap of InNSb from that of InSb is shown by modelling the competing effects of Moss-Burstein band filling and bandgap renormalisation. Finally, bandstructure calculations of the quaternary material GaInNSb, with dilute incorporations of nitrogen and indium, show that the material is suitable for the exploitation of the 8–14 μm atmospheric transmission window. Structural characterisation of GaInNSb shows that this material can be grown lattice matched to GaSb with nitrogen and indium incorporations of 1.8 and 8.4 per cent, respectively. The conducting oxide CdO, grown by metal-organic vapour-phase epitaxy, has also been studied. Analysis and simulation of infrared reflectance data, including conduction band non-parabolicity and Moss-Burstein band filling, reveal bandgap and band-edge effective mass values of 2.16 eV and 0.21 m0, respectively. In addition, high energy 4He+ ion irradiation was used to stabilise the Fermi level in CdO. Carrier statistics calculations were performed and the charge neutrality level was found to be 2.52 eV with respect to the "-point valence band maximum, corresponding to 0.36 eV above the conduction band minimum. The location of the charge neutrality level within the conduction band explains the propensity for high unintentional n-type doping, and the high conductivity observed in CdO

Optoelectronic properties of highly mismatched semiconductor materials

Dilute nitride alloys of III–V semiconductors, and transparent conducting group-II oxides may both be categorised as highly mismatched compounds. The small size and high values of electronegativity of nitrogen and oxygen (see figure), compared to the substituted anion, in dilute nitrides, and the cation, in transparent conducting oxides, give rise to striking properties in these materials. The dilute nitride alloys GaNSb, InNSb, and GaInNSb, grown by molecular beam epitaxy, have been studied. Infrared absorption measurements of GaNSb are presented, showing the divergence of transitions from the valence band to E− and E+ conduction bands with increasing nitrogen incorporation. The fitting of the positions of the valence band to E+ transitions gives a value of 2.6 eV for the coupling parameter in this material. A reduction in the bandgap of InNSb from that of InSb is shown by modelling the competing effects of Moss-Burstein band filling and bandgap renormalisation. Finally, bandstructure calculations of the quaternary material GaInNSb, with dilute incorporations of nitrogen and indium, show that the material is suitable for the exploitation of the 8–14 μm atmospheric transmission window. Structural characterisation of GaInNSb shows that this material can be grown lattice matched to GaSb with nitrogen and indium incorporations of 1.8 and 8.4 per cent, respectively. The conducting oxide CdO, grown by metal-organic vapour-phase epitaxy, has also been studied. Analysis and simulation of infrared reflectance data, including conduction band non-parabolicity and Moss-Burstein band filling, reveal bandgap and band-edge effective mass values of 2.16 eV and 0.21 m0, respectively. In addition, high energy 4He+ ion irradiation was used to stabilise the Fermi level in CdO. Carrier statistics calculations were performed and the charge neutrality level was found to be 2.52 eV with respect to the "-point valence band maximum, corresponding to 0.36 eV above the conduction band minimum. The location of the charge neutrality level within the conduction band explains the propensity for high unintentional n-type doping, and the high conductivity observed in CdO.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Valence band offset of InN/AlN heterojunctions measured by X-ray photoelectron spectroscopy

The valence band offset of wurtzite-InN/AlN (0001) heterojunctions is determined by x-ray photoelectron spectroscopy to be 1.52±0.17 eV. Together with the resulting conduction band offset of 4.0±0.2 eV, a type-I heterojunction forms between InN and AlN in the straddling arrangement

Transition from electron accumulation to depletion at InGaN surfaces

The composition dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1−xN films (0<=x<=1) is investigated using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band minimum (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approximately x=0.3. The results are consistent with the composition dependence of the band edges with respect to the charge neutrality level

Band gap reduction in GaNSb alloys due to the anion mismatch

The structural and optoelectronic properties in GaNxSb1–x alloys (0<=x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1–x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content

Conversation analysis (CA)

Conversation analysis (CA) is an approach to the study of language and social interaction that puts at center stage its sequential development. The chain of initiating and responding actions that characterizes any interaction is a source of internal evidence for the meaning of social behavior as it exposes the understandings that participants themselves give of what one another is doing. Such an analysis requires the close and repeated inspection of audio and video recordings of naturally occurring interaction, supported by transcripts and other forms of annotation. Distributional regularities are complemented by a demonstration of participants' orientation to deviant behavior. CA has long maintained a constructive dialogue and reciprocal influence with linguistic anthropology. This includes a recent convergence on the cross-linguistic and cross-cultural study of social interaction

Centerscope

Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.