T. B. Popova

Depth Profiling of Semiconductor Structures by X-Ray Microanalysis Using the Electron Probe Energy Variation Technique

Depth profiling of semiconductor structures by X-ray microanalysis using the electron probe variation technique followed by mathematical processing of the measurement results is described. Experimental dependences of the relative X-ray intensity on the energy of the electron probe were compared to the Monte Carlo simulation results. Concentration depth profiles were estimated using a priori assumptions, and numerical parameters of the depth distributions were determined from the best fit of calculated curves to the experimental data. The technique was applied to determine Al depth profiles in SiC and GaN samples.

X-ray spectrum microanalysis of semiconductor epitaxial heterostructures on the basis of a monte carlo simulation of electron transport

Specific features of the X-ray spectrum microanalysis of semiconductor heterostructures based on III–V and II–VI alloys with thin epitaxial layers are considered. Simulation of electron transport on the basis of the Monte Carlo method is used to analyze the effect of the layer and substrate on the depth distribution of X-ray generation. Good agreement between the calculated and experimental values of the ratio between the intensities of emission from the layer and bulk sample for simulated Al0.2Ga0.8As structures on the GaAs substrate (with different thicknesses of the layer) is obtained. Methods allowing the performance of a correct microanalysis of the layers with thicknesses in excess of 50 nm and to determine simultaneously the composition and thickness of epitaxial layers are suggested. The methods developed can be used in the analysis of thin layers and in other systems.

Integrated diagnostics of heterostructures with QW layers

Potential of the integrated diagnostics of III–V complex quantum-well (QW) structures used for fabrication of power lasers is demonstrated for the example of GaInP/GaAs/AlGaAs QW structures grown by the metal-organic chemical vapor deposition method. An analysis of cathodoluminescence spectra enabled estimation of the composition of barrier layers, confirmed the existence of a QW, and detected anomalies in its emission associated with compositional changes. An examination of the structures with a transmission electron microscope determined the thickness of barrier layers and the width and composition of the QW, and discovered transition layers near interfaces. The composition of the barrier layers was precisely determined by electron probe microanalysis. The resulting values of the parameters were used in interpretation of X-ray diffraction data, which confirmed the existence of transition regions and revealed composition gradients and partial relaxation in the main part of barrier layers. The integrated study yielded consistent and substantiated data on the layer thickness and composition and data on the quality of interfaces, partial relaxation of the layers, and existence of transition layers and composition gradients.

Electron probe microanalysis of heterostructures with nanolayers

A technique of the electron probe microanalysis of semiconductor heterostructures consisting of nanolayers is described. Features of the microanalysis of such structures are compared to the analysis of structures with thicker layers and of homogeneous samples. Possibilities of the method are illustrated by an example of determination of the layer composition in light-emitting diodes and laser quantum-well InGaAs and ZnCdSe heterostructures. The proposed technique allowed determination of the composition and depth of quantum-well nanosize layers in the samples under study with an accuracy of no worse than 10%. The results of the microanalysis are shown to be in good agreement with the data obtained by other methods.

Cathodoluminescence of laser AIIBVI heterostructures

A Cathodoluminescence (CL) method has been used for studies of ZnSe-based heterostructures with a CdSe fractional-monolayer recombination region. Electron beams with energies of 1–25 keV provide the ability to analyze CL bands associated with different layers of the heterostructure and revealed on the CL spectrum at different electron-beam penetration depth. Comparative analysis of the CL bands both from the recombination region and the upper layers has been used to characterize the transport properties of the structure. The correlation between the density and size distribution of quantum dots and full width at half maximum and spectral position of the CL bands has been studied in detail.

Study of the parameters of nanoscale layers in nanoheterostructures based on II–VI semiconductor compounds

Wide-gap ZnSe-based nanoheterostructures grown by molecular-beam epitaxy are studied by local cathodoluminescence and X-ray microanalysis. It is shown that the used methods allow nondestructive determination of the depth, elemental composition, and geometrical parameters of the nanoscale ZnCdSe layer. The accuracy of the results is verified by transmission electron microscopy. The research techniques are based on the possibility of varying the primary electron-beam energy, which results in changes in the regions of characteristic X-ray and cathodoluminescence generation.

Electron probe microanalysis and local cathodoluminescence studies of multilayer heterostructures based on InGaN/GaN

This paper presents the results of the study on multilayer heterostructures based on InGaN/GaN grown by MOCVD. A new procedure to measure the composition and depth of InGaN quantum wells and AlGaN barrier layers is developed. Features of luminescence from different depths of the multilayer heterostructure are analyzed.