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.Comment: 2 figure

Distorted wurtzite unit cells: Determination of lattice parameters of non-polar a-plane AlGaN and estimation of solid phase Al content

Unlike c-plane nitrides, ``non-polar" nitrides grown in e.g. the a-plane or m-plane orientation encounter anisotropic in-plane strain due to the anisotropy in the lattice and thermal mismatch with the substrate or buffer layer. Such anisotropic strain results in a distortion of the wurtzite unit cell and creates difficulty in accurate determination of lattice parameters and solid phase group-III content (x_solid) in ternary alloys. In this paper we show that the lattice distortion is orthorhombic, and outline a relatively simple procedure for measurement of lattice parameters of non-polar group III-nitrides epilayers from high resolution x-ray diffraction measurements. We derive an approximate expression for x_solid taking into account the anisotropic strain. We illustrate this using data for a-plane AlGaN, where we measure the lattice parameters and estimate the solid phase Al content, and also show that this method is applicable for m-plane structures as well

Facile fabrication of lateral nanowire wrap-gate devices with improved performance

We present a simple fabrication technique for lateral nanowire wrap-gate devices with high capacitive coupling and field-effect mobility. Our process uses e-beam lithography with a single resist-spinning step, and does not require chemical etching. We measure, in the temperature range 1.5-250 K, a subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 $cm^2/Vs$ -- significantly larger than previously reported lateral wrap-gate devices. At depletion, the barrier height due to the gated region is proportional to applied wrap-gate voltage.Comment: 3 pages, 3 figure

Microwave Spectroscopy

Contains reports on five research projects

Microwave Spectroscopy

Contains reports on three research projects