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Title: Photoreflectance and spectroscopic ellipsometry of lattice matched and strained multilayer III-V structures
Author: Garawal, Nirmal Singh
ISNI:       0000 0001 3488 253X
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1997
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Room temperature Photoreflectance and Spectroscopic Ellipsometry were used to study the valence band axial strain deformation potential in pseudomorphic strained In2Ga 8As on GaAs, the band offsets in strained single quantum wells of In 2Ga 8As with AlyGa(1-y)As (y=0, 5, 10 and 20%) barriers on GaAs and the composition and thicknesses of lattice matched (Ga, As, In, Al, P) -based multilayers. The samples were grown by MBE and MOVPE. The photoreflectance spectra from a number of In gGa gAs layers with thicknesses from lOOA to 8000A grown on GaAs substrates were measured. They showed clear, well defined structures attributed to the splitting of the valence band into the Mj=+/-3/2,+/-l/2 manifolds. Their separation was observed to decrease and their overall position to move to lower energy with increasing thickness. Complex GaAs substrate structures were also observed whose shape was attributed to interference. The spectra were modelled using a Kramers-Kronig transformation to deduce the number, magnitude and broadening of the oscillators needed for a least-squares fit using Aspnes' third derivative functional form for a 3d critical point. Excellent fits were obtained which are unrivalled in previous PR analysis. The position of the strained split structures corresponded well with the measured strain from x-ray analysis and theory. From these splittings, values of the axial deformation potential, b, were obtained in the range -2.5 to -1.54eV. The photoreflectance from the single quantum wells showed clear, complex spectra. Good fits were obtained using the third derivative functional form (TDFF) for a 2d critical point. Both symmetry allowed and forbidden transitions were observed. The predicted transitions were calculated using an effective mass formalism. Reasonable agreement with the experimentally observed confined transition energies was found. The band offsets were estimated by allowing the theoretical offsets, determined from the theory of Van der Walle, to vary until a good match with observed transitions was obtained. Conduction to valence band offset values of 60:40 +/-8% were obtained, well within the range predicted by other workers. Spectroscopic ellipsometry has been used to measured the compositions and thicknesses of two-, three-, and four-layer structures consisting of Al2Ga8As/GaAs and In53Ga47As/Al48Ga52As/InP lattice matched materials. A simple procedure was developed to obtain the dielectric values of Al48In 52AS by scaling InP values. These were used to simulate the test structures. Very good agreement with destructive techniques have been obtained. These were compared to the thickness values obtained using actual measured Al48In52As reference data.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Solid-state physics