1,171 research outputs found
ab initio Electronic Transport Model with Explicit Solution to the Linearized Boltzmann Transport Equation
Accurate models of carrier transport are essential for describing the
electronic properties of semiconductor materials. To the best of our knowledge,
the current models following the framework of the Boltzmann transport equation
(BTE) either rely heavily on experimental data (i.e., semi-empirical), or
utilize simplifying assumptions, such as the constant relaxation time
approximation (BTE-cRTA). While these models offer valuable physical insights
and accurate calculations of transport properties in some cases, they often
lack sufficient accuracy -- particularly in capturing the correct trends with
temperature and carrier concentration. We present here a general transport
model for calculating low-field electrical drift mobility and Seebeck
coefficient of n-type semiconductors, by explicitly considering all relevant
physical phenomena (i.e. elastic and inelastic scattering mechanisms). We first
rewrite expressions for the rates of elastic scattering mechanisms, in terms of
ab initio properties, such as the band structure, density of states, and polar
optical phonon frequency. We then solve the linear BTE to obtain the
perturbation to the electron distribution -- resulting from the dominant
scattering mechanisms -- and use this to calculate the overall mobility and
Seebeck coefficient. Using our model, we accurately calculate electrical
transport properties of the compound n-type semiconductors, GaAs and InN, over
various ranges of temperature and carrier concentration. Our fully predictive
model provides high accuracy when compared to experimental measurements on both
GaAs and InN, and vastly outperforms both semi-empirical models and the
BTE-cRTA. Therefore, we assert that this approach represents a first step
towards a fully ab initio carrier transport model that is valid in all compound
semiconductors
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Formation of diluted III–V nitride thin films by N ion implantation
iluted III–Nₓ–V₁ˍₓ alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1−yAs. In all three cases the fundamental band-gap energy for the ion beam synthesized III–Nₓ–V₁ˍₓ alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNₓAs1−x and InNₓP₁ˍₓalloys. In GaNₓAs₁ˍₓ the highest value of x (fraction of “active” substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850 °C. The highest value of x achieved in InNₓP₁ˍₓ was higher, 0.012, and the NP was found to be stable to at least 850 °C. In addition, the N activation efficiency in implantedInNₓP₁ˍₓ was at least a factor of 2 higher than that in GaNₓAs₁ˍₓ under similar processing conditions. AlyGa1−yNₓAs₁ˍₓ had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1−yNₓAs₁ˍₓalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the ‘‘Photovoltaic Materials
Focus Area’’ in the DOE Center of Excellence for the Synthesis
and Processing of Advanced Materials, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported
by Midwest Research Institute under subcontractor
No. AAD-9-18668-7 from NREL
Effect of Native Defects on Optical Properties of InxGa1-xN Alloys
The energy position of the optical absorption edge and the free carrier
populations in InxGa1-xN ternary alloys can be controlled using high energy
4He+ irradiation. The blue shift of the absorption edge after irradiation in
In-rich material (x > 0.34) is attributed to the band-filling effect
(Burstein-Moss shift) due to the native donors introduced by the irradiation.
In Ga-rich material, optical absorption measurements show that the
irradiation-introduced native defects are inside the bandgap, where they are
incorporated as acceptors. The observed irradiation-produced changes in the
optical absorption edge and the carrier populations in InxGa1-xN are in
excellent agreement with the predictions of the amphoteric defect model
Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon
The magnetic rare earth element gadolinium (Gd) was doped into thin films of
amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C)
using magnetron co-sputtering. The Gd acted as a magnetic as well as an
electrical dopant, resulting in an enormous negative magnetoresistance below a
temperature (). Hydrogen was introduced to control the amorphous carbon
bonding structure. High-resolution electron microscopy, ion-beam analysis and
Raman spectroscopy were used to characterize the influence of Gd doping on the
\textit{a-}GdC(:H) film morphology, composition, density and
bonding. The films were largely amorphous and homogeneous up to =22.0 at.%.
As the Gd doping increased, the -bonded carbon atoms evolved from
carbon chains to 6-member graphitic rings. Incorporation of H opened up the
graphitic rings and stabilized a -rich carbon-chain random network. The
transport properties not only depended on Gd doping, but were also very
sensitive to the ordering. Magnetic properties, such as the spin-glass
freezing temperature and susceptibility, scaled with the Gd concentration.Comment: 9 figure
Structural and Electronic Properties of Amorphous and Polycrystalline In2Se3 Films
Structural and electronic properties of amorphous and single-phase
polycrystalline films of gamma- and kappa-In2Se3 have been measured. The stable
gamma phase nucleates homogeneously in the film bulk and has a high
resistivity, while the metastable kappa phase nucleates at the film surface and
has a moderate resistivity. The microstructures of hot-deposited and
post-annealed cold-deposited gamma films are quite different but the electronic
properties are similar. The increase in the resistivity of amorphous In2Se3
films upon annealing is interpreted in terms of the replacement of In-In bonds
with In-Se bonds during crystallization. Great care must be taken in the
preparation of In2Se3 films for electrical measurements as the presence of
excess chalcogen or surface oxidation may greatly affect the film properties.Comment: 23 pages and 12 figure
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