G. Maciejewski

Composition fluctuation in InGaN quantum wells made from molecular beam or metalorganic vapor phase epitaxial layers

Using strain analysis on high resolution electron microscopy images and finite element modeling of InGaN quantum wells (QWs), it is shown that the In composition changes inside the layers can be accurately determined. The analyzed samples were nominally grown with 15%–17% In composition by molecular beam or metalorganic vapor phase epitaxy. Inside these QWs, the In composition is not homogeneous. Finite element modeling strongly suggests that the measured strain corresponds most probably to InN clusters whose size depends on the growth method.

The dislocations of low-angle grain boundaries in GaN epilayers: a HRTEM quantitative study and finite element stress state calculation

Abstract During epitaxy of GaN on sapphire grains form a mosaic structure. The distance between edge dislocations in these boundaries is from 2 to 15 nm. The strain around the dislocations is quantitatively measured by processing of HRTEM images. The dislocation core distribution maps and in plane Burgers vectors components are derived from the experimental strain tensor by applying the continuum dislocation theory. Experimental results were compared with the atomic models of edge dislocations calculated using a modified Stillinger–Weber potential for different atomic configurations of the cores. It is concluded that the strain field extracted from simulated images matches with that of observed dislocations. Starting from experimental distortion distribution data, the finite element calculations are used to estimate the stress around the boundaries.

Piezoelectric field around threading dislocation in GaN determined on the basis of high‐resolution transmission electron microscopy image

A new method of determining the piezoelectric field around dislocations from high‐resolution transmission electron microscopy images is presented. In order to determine the electrical potential distribution near a dislocation core, we used the distortion field, obtained using the geometrical phase method and the non‐linear finite element method. The electrical field distribution was determined taking into account the inhomogeneous strain distribution, finite geometry of the sample and the full couplings between elastic and electrical fields. The results of the calculation for a transmission electron microscopy thin sample are presented.

Finite Element Simulation of Residual Stresses in Epitaxial Layers

A nonlinear finite element approach presented here is based on the constitutive equations for anisotropic hyperelastic materials. By digital image processing the elastic incompatibilities (lattice mismatch) are extracted from the HRTEM image of GaN epilayer. Such obtained tensorial field of dislocation distribution is used next as the input data to the FE code. This approach is developed to study the stress distribution associated with lattice defects in highly mismatched heterostructures applied as buffer layers for the optically active structures.

Contribution to quantitative measurement of the In composition in GaN/InGaN multilayers

The In composition is investigated in GaN/InGaN multi-quantum wells (QWs) by measurement of the local lattice distortion in high-resolution electron microscopy (HREM) images taken along the [1120] zone axis by image processing. The direct peak-finding procedure is more adequate for analysing images taken in the [1120] zone axis in comparison with the geometric-phase method since the information from different beams must be averaged. The finite element (FE) modelling and image simulation were combined in order to determine the error bars of the composition evaluation

Pressure and Temperature Tuned Semiconductor Laser Diodes

We present results of theoretical studies of the pressure and temperature tuned laser diodes (LDs) based on InGaP/AlGaInP heterostructures taking into account mounting‐induced strains. Our studies reveal that mounting‐induced strains play an important role in the quantitative description of these LDs. We determine their influence on the laser wave‐length tuning by hydrostatic pressure.

Indium distribution inside quantum wells: The effect of growth interruption in MBE

Quantitative analysis of high resolution electron microscopy image has been carried out to measure the indium distribution inside InGaN/GaN quantum well. The analyzed samples were nominally grown with 15% indium composition by molecular beam epitaxy with interruptions during the InxGa1-xN layer growth. The strain distribution is not homogeneous inside the quantum wells, and indium rich clusters can be observed. Areas with almost no indium concentration were observed corresponding to the growth interruption. A comparison with samples grown by metalorganic chemical vapor deposition is attempted.