We demonstrate the mutual passivation phenomenon of Ge donors and isovalent N in highly mismatched alloy GaNxAs1−x doped with Ge. Layers of this alloy were formed by the sequential implantation of Ge and N ions followed by pulsed laser melting and rapid thermal annealing. The mutual passivation effect results in the electrical deactivation of GeGa donors (Ge on Ga sites) and suppression of the NAs (N on As sites) induced band gap narrowing through the formation of GeGa–NAs nearest neighbor pairs. These results in combination with the analogous effect observed in Si-doped GaNxAs1−x provide clear evidence of the general nature of the mutual passivation phenomenon in highly mismatched semiconductor alloys.

Abstract The valence band anticrossing model (VBAC) is applied to explain the composition‐dependent trends in dilute GaSb x As 1–x and GaBi x As 1–x alloys. Photomodulated reflectance spectroscopy (PR) of GaSb x As 1–x shows a reduction of the fundamental bandgap energy as well as an increase of the spin‐orbit splitting energy with increasing x . The VBAC model predicts that these shifts are the result of a hybridization of the extended valence band states of GaAs with the localized states of the impurity atoms, which induce an upward movement of the valence band edge. Extrapolation of the model to other III‐(Sb,Bi)‐V alloys is also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent work has shown that GaN1−xAsx can be grown across the entire composition range by low temperature molecular beam epitaxy with intermediate compositions being amorphous, but control of the electrical properties through doping is critical for functionalizing this material. Here we report the bipolar doping of GaN1−xAsx with high As content to conductivities above 4 S/cm at room temperature using Mg or Te. The carrier type was confirmed by thermopower measurements. Doping requires an increase in Ga flux during growth resulting in a mixed phase material of polycrystalline GaAs:N embedded in amorphous GaN1−xAsx.

We have calculated the effects of quantum confinement on maximum achievable free carrier concentrations in semiconductor nanowires. Our calculations are based on the amphoteric defect model, which describes the thermodynamic doping limit in semiconductors in terms of the compensation of external dopants by native defects. We find that the generation of amphoteric native defects strongly limits maximum achievable carrier concentrations for nanowires with small widths where quantum confinement is appreciable. The magnitude of this effect in a given material is found to be determined by two material properties: the effective mass of the free carriers, and the position of the conduction (n-type) or valence band (p-type) edge on the absolute energy scale. These results offer a simple, predictive guideline for designing nanostructure devices and contacts where high doping levels are needed.

This is the third paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have considered a sample of about 1000 SNe and used an optimal subsample of 726 SNe (274 SNe Ia, 116 SNe Ibc, and 324 SNe II) to determine our rates. We study the trend of the rates as a function of a few quantities available for our galaxy sample, such as luminosity in the B and K bands, stellar mass, and morphological class. We discuss different choices (SN samples, input SN luminosity functions, inclination correction factors) and their effect on the rates and their uncertainties. A comparison between our SN rates and the published measurements shows that they are consistent with each other to within uncertainties when the rate calculations are done in the same manner. Nevertheless, our data demonstrate that the rates cannot be adequately described by a single parameter using either galaxy Hubble types or B - K colours. A secondary parameter in galaxy "size", expressed by luminosity or stellar mass, is needed to adequately describe the rates in the rate-size relation: the galaxies of smaller sizes have higher SN rates per unit mass or per unit luminosity. The trends of the SN rates in galaxies of different Hubble types and colours are discussed. We examine possible causes for the rate-size relation. Physically, such a relation for the core-collapse SNe is probably linked to the correlation between the specific star-formation rate and the galaxy sizes, but it is not clear whether the same link can be established for SNe Ia. We discuss the two-component ("tardy" and "prompt") model for SN Ia rates, and find that the SN Ia rates in young stellar populations might have a strong correlation with the core-collapse SN rates. We derive volumetric and Milky Way rates ... (abridged)

Abstract The effect of alloying a small amount of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in MBE‐grown ZnO x Se 1− x epitaxial films (0 ≤ x ≤ 0.0135) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band‐gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by the O incorporation. Both effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction band edge. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi Stabilization Energy (E{sub FS}), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E{sub FS} is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.

We have studied the effects of composition and hydrostatic pressure on the direct optical transitions at the Γ point of the Brillouin zone in MBE-grown ZnO_xSe_1-x and ion-implantation-synthesized Zn_1-yMn_yO_xTe_1-x alloys. We observe a large O-induced band-gap reduction and a change in the pressure dependence of the fundamental band gap of the II-O-VI alloys. The effects are similar to those previously observed and extensively studied in highly mismatched III-N-V alloys. Our results are well explained in terms of the band anticrossing model that considers an anticrossing interaction between the highly localized oxygen states and the extended states of the conduction band of II-VI compounds. The O-induced modification of the conduction band structure offers an interesting possibility of using small amounts of O to engineer the optoelectronics properties of group II-O-VI alloys.

We report the realization of a new mult-band-gap semiconductor. Zn(1-y)Mn(y)OxTe1-x alloys have been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the Zn(1-y)Mn(y)Te host. When only 1.3% of Te atoms are replaced with oxygen in a Zn0.88Mn0.12Te crystal the resulting band structure consists of two direct band gaps with interband transitions at approximately 1.77 and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model. With multiple band gaps that fall within the solar energy spectrum, Zn(1-y)Mn(y)OxTe1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%.

We have synthesized ternary and quaternary diluted II-VI oxides using the combination of O ion implantation and pulsed laser melting. CdOxTe1−x thin films with x up to 0.015, and the energy gap reduced by 150 meV were formed by O+-implantation in CdTe followed by pulsed laser melting. Quaternary Cd0.6Mn0.4OxTe1−x and Zn0.88Mn0.12OxTe1−x with mole fraction of incorporated O as high as 0.03 were also formed. The enhanced O incorporation in Mn-containing alloys is believed to be due to the formation of relatively strong Mn-O bonds. Optical transitions associated with the lower (E−) and upper (E+) conduction subbands resulting from the anticrossing interaction between the localized O states and the extended conduction states of the host are clearly observed in these quaternary diluted II-VI oxides. These alloys fulfill the criteria for a multiband semiconductor that has been proposed as a material for making high efficiency, single-junction solar cells.

The authors have recently discovered a new effect in the dilute InGaAsN alloy system in which electrically active substitutional Si donors and isoelectronic N atoms passivate each other's activity. This is manifested in a drastic reduction of the free electron concentration and, simultaneously, an increase in the fundamental bandgap in Si-doped InGaAsN alloys. Systematic studies of the mutual passivation effect in Si-doped InGaAsN alloys show that the passivation process is controlled by the diffusion of Si to the nearest neighbours of N-occupied sites, forming nearest neighbour Si–N pairs. Analytical calculations of the passivation process based on Ga-vacancy-mediated diffusion show good agreement with the experimental results. It is shown that the mutual passivation provides a method to precisely control electrical properties of InGaAsN:Si. Investigations were made of scattering mechanisms limiting electron mobility in InGaAsN through a judicious choice of the annealing conditions to vary the electron concentration by more than two orders of magnitude. The mobility of free electrons in InGaAsN is quantitatively explained on the basis of the band anticrossing model.

We report the observation of a current-driven metal (M)-insulator (I) phase oscillation in two-terminal devices incorporating individual WxV1-xO2 nanobeams connected to parallel shunt capacitors. The frequency of the phase oscillation reaches above 5 MHz for 1 Im long devices. The M-I phase oscillation, which coincides with the charging/discharging of the capacitor, occurs through the axial drift of a single M-I domain wall driven by Joule heating and the Peltier effect.

We report photomodulation spectroscopy measurements of the pressure dependence of the optical transition in Zn1−yMnyOxTe1−x alloys that is associated with the lowest Γ conduction band (termed E− subband). The pressure-induced energy shift of the E− transition is nonlinear and much weaker as compared to the change of the direct band gap of Zn0.88Mn0.12Te. The weak pressure dependence of the E− transition can be fully understood based on the band anticrossing model in which the E− subband results from an interaction between the extended ZnMnTe conduction-band states and the localized O electronic states.

We study the observables of 158 relatively normal Type Ia supernovae (SNe Ia) by dividing them into two groups in terms of the expansion velocity inferred from the absorption minimum of the Si ii λ6355 line in their spectra near B-band maximum brightness. One group ("Normal") consists of normal SNe Ia populating a narrow strip in the Si ii velocity distribution, with an average expansion velocity 〈v〉 = 10, 600 ± 400 km s−1 near B maximum; the other group ("HV") consists of objects with higher velocities, v ≳ 11, 800 km s−1. Compared with the Normal group, the HV one shows a narrower distribution in both the peak luminosity and the luminosity decline rate Δm15. In particular, their B−V colors at maximum brightness are found to be on average redder by ∼ 0.1 mag, suggesting that they either are associated with dusty environments or have intrinsically red B−V colors. The HV SNe Ia are also found to prefer a lower extinction ratio RV ≈ 1.6 (versus ∼ 2.4 for the Normal ones). Applying such an absorption-correction dichotomy to SNe Ia of these two groups remarkably reduces the dispersion in their peak luminosity from 0.178 mag to only 0.125 mag.