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Arnab Bhattacharya

Publications and source records attributed to Arnab Bhattacharya.

115 records · Page 7Linked to original sources
arXiv2008

Non-intrinsic superconductivity in InN epilayers: role of Indium Oxide

In recent years there have been reports of anomalous electrical resistivity and the presence of superconductivity in semiconducting InN layers. By a careful correlation of the temperature dependence of resistivity and magnetic susceptibility with structural information from highresolution x-ray diffraction measurements we show that superconductivity is not intrinsic to InN and is seen only in samples that show traces of oxygen impurity. We hence believe that InN is not intrinsically a superconducting semiconductor.

cond-mat.mtrl-sci↗
arXiv2007

The role of hydrostatic stress in determining the bandgap of InN epilayers

We establish a correlation between the internal stress in InN epilayers and their optical properties such as the measured absorption band edge and photoluminescence emission wavelength. By a careful evaluation of the lattice constants of InN epilayers grown on c-plane sapphire substrates under various conditions by metalorganic vapor phase epitaxy we find that the films are under primarily hydrostatic stress. This results in a shift in the band edge to higher energy. The effect is significant, and may be responsible for some of the variations in InN bandgap reported in the literature.

cond-mat.mtrl-sci↗
arXiv2007

Influence of growth parameters on structural properties and bandgap of InN epilayers deposited in a showerhead MOVPE system

From a detailed analysis of InN epilayers deposited in a close-coupled showerhead metalorganic vapour phase epitaxy (MOVPE) system under various conditions we investigate the effect of growth parameters on the lattice constants of the InN layer. The layers are under significant internal hydrostatic stress which influences the optical properties. Samples typically fall into two broad categories of stress, with resultant luminescence emission around 0.8eV and 1.1eV. We can correlate the internal stress in the layer and the value of the optical absorption edge, and the PL emission wavelength.

cond-mat.mtrl-sci↗
arXiv2005

Alloy disorder effects on the room temperature optical properties of GaInNAs quantum wells

The effect of alloy disorder on the optical density of states and the average room temperature carrier statistics in GaInNAs quantum wells is discussed. A red shift between the peak of the room temperature photoluminescence and the surface photovoltage spectra, that systematically increases with the nitrogen content within the quantum wells is observed. The relationship between this Stokes' shift and the absorption linewidth in different samples suggests that the photoexcited carriers undergo a continuous transition, from being in quasi-thermal equilibrium with the lattice to being completely trapped by the quantum dot-like potential fluctuations, as the nitrogen fraction in the alloy is increased. The values of the 'electron temperature' inferred from the photoluminescence spectra are found to be consistent with this interpretation.

cond-mat.mtrl-sci↗
arXiv2005

Growth kinetics effects on self-assembled InAs/InP quantum dots

A systematic manipulation of the morphology and the optical emission properties of MOVPE grown ensembles of InAs/InP quantum dots is demonstrated by changing the growth kinetics parameters. Under non-equilibrium conditions of a comparatively higher growth rate and low growth temperature, the quantum dot density, their average size and hence the peak emission wavelength can be tuned by changing efficiency of the surface diffusion (determined by the growth temperature) relative to the growth flux. We further observe that the distribution of quantum dot heights, for samples grown under varying conditions, if normalized to the mean height, can be nearly collapsed onto a single Gaussian curve.

cond-mat.mtrl-sci↗
arXiv2005

Another origin of bimodal size distribution in InAs self-assembled quantum dots

The evolution of InAs quantum dots grown on InP substrates by metal-organic vapour phase epitaxy is studied as a function of InAs coverage. Under specific growth conditions, the onset of the two- to three-dimensional transition is seen to proceed via two distinct pathways: through (i) an abrupt appearance of quantum dots as expected in the usual Stranski-Krastanov growth picture and (ii) a continuous evolution of small surface features into well developed quantum dots. The average size of the features in both these families increases with coverage, leading to a bimodal distribution in dot sizes at an intermediate stage of growth evolution that eventually becomes a unimodal distribution as more material is deposited. Complementary information obtained from independent measurements of photoluminescence spectra and surface morphology is correlated and is found to be consistent with the picture of growth proposed.

cond-mat.mtrl-sci↗