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Title: Characterisation of III-V quaternary multilayer semiconductor device materials by X-ray diffraction
Author: Swaminathan, S.
ISNI:       0000 0001 3493 124X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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Optoelectronic devices find extensive use in optical fibre communication systems as infrared sources, in view of a relatively low attenuation of the optical fibres for such sources in the spectral range 1.0 - 1.4 pm. In the study of optoelectronic device materials, minute variations in the lattice parameter of different layers cause lattice strain, which, along with other factors namely thermal gradients, a high density of recombining carriers in the active layer promote the motion, multiplication and growth of defects into network clusters. In this thesis a double crystal plane wave synchrotron radiation technique has been found to be capable of accurately characterizing individual layers in a multilayer structure such as in an optoelectronic device consisting of many layers of InGaAs, InGaAsP and InP grown over an InP substrate. This non-destructive method can separate images of the ternary and quaternary layers from the substrate (InP) thereby identifying the location of any defects as well as detailed identification of dislocation-type defects. The observed presence of a cross hatch pattern of interfacial misfit dislocations has been strongly correlated to the degradation of the device. The technique also enables a very precise plot of the rocking curves which provides invaluable information about the assessment of the thickness, compositional variation in the ternary or quaternary epitaxial layers and also of their crystalline perfection. The technique is capable of mapping lattice parameter differences of the order of 10-8. A fairly accurate assessment of the inhomogeneity and non-uniformity of quaternary multilayers grown by liquid phase epitaxy has been made by this technique. About 54Z variations in the total quaternary layer thickness was observed for a double heterostructure laser and about 39Z for a thick graded single layer quaternary specimen. For multilayer structures showing complicated rocking curves, it has been demonstrated that a selective etching of the layers in sequence helps identify the individual layer characteristics. A theoretical calculation of rocking curves from heteroepitaxial layers is presented. Initial data from experimental rocking curves are used to calculate rocking curves for the multilayer structure and then compared with experimental curves. The input data are slightly adjusted about their initial values until a reasonable fit with experimental curves is achieved. The initial data consist of the knowledge of the thickness and mismatch variations of each layer in the multilayer structure. The mismatch variations for the layers as obtained by selective etching have been effectively used to simulate experimental rocking curves. An accurate interpretation of layer characteristics from such a simulated fit has thus been made possible. Simulation studies have thus been found to offer a powerful and nondestructive method of a detailed and accurate assessment of layer thickness and compositional variations by comparison with experimental rocking curves. Studies on a number of specimens have shown satisfactory agreement: the predicted thicknesses have been found to be generally of the same order as reported by Plessey, Caswell, where the devices were grown, and in cases where the data were either disputed or not available, experimental verification of the layer thickness made by selective etching, was found to be in agreement with the thickness predicted by the simulated studies.
Supervisor: Shurmer, Harold Victor ; Bowen, David Keith Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering