In this thesis, calculations of Auger recombination rates in semiconductor quantum wells are presented. Chapter One introduces Auger recombination, and the reasons for studying the Auger process are explained. Basically, Auger recombination is a non- radiative recombination mechanism that becomes more important as the carrier density increases and the bandgap decreases. In direct gap semiconductors, the Auger process has an activation energy, and the resulting highly temperature dependent Auger process is thought to be a possible cause of the high temperature sensitivity of long wavelength semiconductor lasers that are being considered for use as sources in optical fibre communications systems. In Chapter Two, an expression is derived for the CHSH Auger recombination rate in a quantum well (QW) heterostructure. The possible Auger processes in a QW are discussed as are the differences between Auger recombination in a QW and in bulk semiconductors, and the magnitudes of QW and bulk Auger rates are compared. In Chapter Three, the theory of Auger recombination is extended to the case of a quantum well wire (QWW), a semiconductor structure in which carriers are free to move in one direction only. It is found that there are no significant physical differences between Auger recombination in a QW and in a QWW. The ratio of QW and QWW Auger rates is evaluated. Numerical results for Auger transition rates in 1.3µm and 1.55µm In- GaAsP/InP QWs and QWWs are presented in Chapter Four, and comparison with experimental values is made. In particular, the result found in Chapter Two, that, under certain conditions, the Auger rates in the QW and the bulk are approximately the same is found to agree with experimental results from the literature. The derivation of the CHSH Auger transition rates in QWs and QWWs that was presented in Chapters Two and Three required a number of approximations concerning the carrier statistics and the semiconductor bandstructure. In Chapter Five, these approximations are examined, and, although it is found that the use of non-degenerate carrier statistics is reasonably accurate, the assumption of parabolic energy bands can lead to overestimates of .the Auger transition rates. The first five chapters constitute the first part of the thesis, concerning Auger recombination in low-dimensional semiconductor structures. In the second part of the thesis, the realistic bandstructure of low-dimensional semi conductor structures, such as superlattices, is examined. The method used is described in Chapter Six, and is based on an empirical pseudopotential method. Results for the GaAs/AlAs superlattice are presented in Chapter Seven.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

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Molecular beam epitaxy (MBE) grown CaF₂-CdF₂ superlattices (SLs) and CaF₂ thin films doped with Eu ions were investigated by laser spectroscopic techniques. Eu ions were selectively doped into CaF₂ layers and were used as an optical probe to the SLs and thin films. Physical properties of the SLs and thin films were inferred from optical transitions of divalent and trivalent Eu centres. The 4ƒ⁶5d → 4ƒ⁷ transition of Eu²⁺ has shown strain dependent peak shifts of the zero phonon line. These shifts were thought to be a result of deformation in the crystal structure primarily due to the lattice mismatch with the Si substrate. Based on the amount of shifts, the strains associated with the MBE samples were calculated. Photoluminescence (PL) bleaching and its recovery of the same transition of Eu²⁺ in SLs were also explored. At low temperature the bleaching is best described as bi-exponential decay. Localisation of the liberated electrons from the 4ƒ⁶5d absorption band was considered for the bleaching effect. It was observed that at elevated temperatures the PL intensity of the 4ƒ⁶5d → 4ƒ⁷ transition was recovered. Combined excitation-emission spectroscopy (CEES) was employed to investigate trivalent Eu centres in SLs. The strong ⁷F₀ → ⁵D₁ excitation and the ⁵D₀ → ⁷F₁ emission of Eu³⁺ were studied. A novel centre, which is assigned as I, of Eu³⁺ in SL was observed and investigated in comparison with the cubic centre (O centre) of Eu³⁺. Relative to the O centre the I centre has shown a strong thickness dependent PL which can be demonstrated with a mono layer (1 ML = 3.15 Å) resolution. Possible transformation of the I centre to the O centre was also observed by additional thermal and UV excitations. The I and the O centres are proposed as the same centre except for having an electron in the vicinity of the I centre.

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Molecular beam epitaxy (MBE) grown CaF₂-CdF₂ superlattices (SLs) and CaF₂ thin films doped with Eu ions were investigated by laser spectroscopic techniques. Eu ions were selectively doped into CaF₂ layers and were used as an optical probe to the SLs and thin films. Physical properties of the SLs and thin films were inferred from optical transitions of divalent and trivalent Eu centres. The 4ƒ⁶5d → 4ƒ⁷ transition of Eu²⁺ has shown strain dependent peak shifts of the zero phonon line. These shifts were thought to be a result of deformation in the crystal structure primarily due to the lattice mismatch with the Si substrate. Based on the amount of shifts, the strains associated with the MBE samples were calculated. Photoluminescence (PL) bleaching and its recovery of the same transition of Eu²⁺ in SLs were also explored. At low temperature the bleaching is best described as bi-exponential decay. Localisation of the liberated electrons from the 4ƒ⁶5d absorption band was considered for the bleaching effect. It was observed that at elevated temperatures the PL intensity of the 4ƒ⁶5d → 4ƒ⁷ transition was recovered. Combined excitation-emission spectroscopy (CEES) was employed to investigate trivalent Eu centres in SLs. The strong ⁷F₀ → ⁵D₁ excitation and the ⁵D₀ → ⁷F₁ emission of Eu³⁺ were studied. A novel centre, which is assigned as I, of Eu³⁺ in SL was observed and investigated in comparison with the cubic centre (O centre) of Eu³⁺. Relative to the O centre the I centre has shown a strong thickness dependent PL which can be demonstrated with a mono layer (1 ML = 3.15 Å) resolution. Possible transformation of the I centre to the O centre was also observed by additional thermal and UV excitations. The I and the O centres are proposed as the same centre except for having an electron in the vicinity of the I centre.