4 research outputs found
Effect of dislocations on electrical and electron transport properties of InN thin films. I. Strain relief and formation of a dislocation network
The strain-relaxation phenomena and the formation of a dislocation network in 2H-InN epilayers
during molecular beam epitaxy are reported. Plastic and elastic strain relaxations were studied by
reflection high-energy electron diffraction, transmission electron microscopy, and high resolution
x-ray diffraction. Characterization of the surface properties has been performed using atomic force
microscopy and photoelectron spectroscopy. In the framework of the growth model the following
stages of the strain relief have been proposed: plastic relaxation of strain by the introduction of
geometric misfit dislocations, elastic strain relief during island growth, formation of threading
dislocations induced by the coalescence of the islands, and relaxation of elastic strain by the
introduction of secondary misfit dislocations. The model emphasizes the determining role of the
coalescence process in the formation of a dislocation network in heteroepitaxially grown 2H-InN.
Edge-type threading dislocations and dislocations of mixed character have been found to be
dominating defects in the wurtzite InN layers. It has been shown that the threading dislocation
density decreases exponentially during the film growth due to recombination and, hence,
annihilation of dislocations, reaching 109 cm−2 for 2200 nm thick InN films.Unión Europea NMP4-CT2003-505614Unión Europea NMP4-CT-2004-500101Comisión Interministerial de Ciencia y Tecnología MAT2004-01234 Españ
Effect of dislocations on electrical and electron transport properties of InN thin films. II. Density and mobility of the carriers
The influence of dislocations on electron transport properties of undoped InN thin films grown by
molecular-beam epitaxy on AlN 0001 pseudosubstrates is reported. The microstructure and the
electron transport in InN 0001 films of varying thickness were analyzed by transmission electron
microscopy and variable temperature Hall-effect measurements. It was found that crystal defects
have strong effects on the electron concentration and mobility of the carriers in the films. In
particular, the combined analysis of microscopy and Hall data showed a direct dependence between
free carrier and dislocation densities in InN. It was demonstrated that threading dislocations are
active suppliers of the electrons and an exponential decay of their density with the thickness implies
the corresponding decay in the carrier density. The analysis of the electron transport yields also a
temperature-independent carrier concentration, which indicates degenerate donor levels in the
narrow band-gap InN material. The relative insensitivity of the mobility with respect to the
temperature suggests that a temperature-independent dislocation strain field scattering dominates
over ionized impurity/defect and phonon scattering causing the increase of the mobility with rising
layer thickness due to the reducing dislocation density. Room temperature mobilities in excess of
1500 cm2 V−1 s−1 were obtained for 800 nm thick InN layers with the dislocation densities of
3 109 cm−2.Deutsche Forschungsgemeinschaft AM105 ∕ 1-1, AlemaniaComisión Interministerial de Ciencia y Tecnología MAT2004-01234, EspañaUnión Europea NMP4-CT-2003- 505641Unión Europea NMP4-CT-2004-50010
Electronic and photoconductive properties of ultrathin InGaN photodetectors
We report on the compositional dependencies of electron transport and photoconductive properties for ultrathin metal-semiconductor-metal photodetectors based on In-rich InxGa1-xN alloys. For a In0.64Ga0.36N/GaN structure, the rise time close to the RC constant at low fields has been measured along with a transparency of similar to 77% and an absorbance of similar to 0.2 at a wavelength of 632 nm. The electron density profiles and low-field mobilities for different compositions of InGaN have been calculated by numerically solving the Schrodinger and Poisson equations and applying the ensemble Monte Carlo method, respectively. It was demonstrated that in ultrathin InxGa1-xN/GaN (0.5 < x < 1) heterostructures, in contrast to bulk InN exhibiting a strong surface electron accumulation, free electrons mostly tend to accumulate at the buried InGaN/GaN interface. We have also found that the low-field mobility in the InGaN/GaN heterostructures is strongly limited by the buried interface roughness which causes more than 95% of all scattering events occurred by two-dimensional electron transport under low electric field conditions.Comisión Interministerial de Ciencia y Tecnología (CICYT) MAT2007-60643 Españ
Coalescence aspects of III-nitride epitaxy
In this work, coalescence aspects of wurtzite-III-nitride epitaxy are addressed. The coalescence phenomena have been studied in thin epilayers by means of electron and atomic force microscopies, and electron and x-ray diffractions. This study generalizes the growth parameters responsible for the rapid coalescence of III-nitride films, and describes the coalescence qualitatively and, partly, analytically for the case of heteroepitaxy in nonequilibrium conditions. Coalescence time and the corresponding diffusion coefficients at elevated temperatures were estimated for GaN and InN depositions. The rate of coalescence has been found to impact on the structure and morphology of III-nitride epilayers. A simple growth model was suggested to explain the formation of domain boundaries and (0001) stacking faults formed during the coalescence. In particular, it is shown that two adjacent and tilted, hexagonal-shaped 2H domains may form a noncoherent boundary explicitly along a {1100} plane. We also suggest that the interaction between tilted domains induces the localized lateral growth of the most epitaxially oriented domain forming a basal (0001) stacking fault followed by the formation of surface macrosteps, and consequently the termination of a threading dislocation by its dissociation and propagation under the formed (0001) stacking fault.German Research Foundation (DFG) DFG Grant No. AM105 / 1-1 AlemaniaComisión Interministerial de Ciencia y Tecnología (CICYT) No. MAT2004-01234 EspañaUnión Europea NICOP No. 00014-03-1-030