Photorefractive semiconductors: Materials, electronic, and optical transport
Abstract
A new and novel material system (low-temperature-grown AlGaAs/GaAs quantum wells) has been developed for photorefractive applications. Ultrafast electron recombination lifetimes in combination with sharp excitonic features, a goal which was considered mutually exclusive, has been achieved by engineering low-temperature-grown AlAs/GaAs quantum wells. Transient enhanced diffusion, a phenomenon, in which quantum-well intermixing and roughening is observed during annealing of the AlAs/GaAs quantum wells has been studied in detail. The objective of this work is twofold. One, to further understand the vacancy decay kinetics in transient enhanced diffusion and to observe it in laser-annealed quantum-wells and the second to use the quantum wells as a gain medium in order to develop a holographic vertical cavity surface emitting laser (HVCSEL). Intermixing of arsenic-rich nonstoichiometric AlAs/GaAs quantum wells grown at low substrate temperature around 300°C is enhanced by several orders of magnitude relative to the diffusion in nonstoichiometric structures grown at ordinary substrate temperatures. The transient enhanced intermixing is attributed to a supersaturation of group-III vacancies incorporated into the crystal lattice by the low temperature growth conditions. The enhanced diffusion decays during moderate-temperature annealing by a focussed laser beam. The diffusion data got by laser annealing compares quite well with that got by conventional rapid thermal annealing. Potential uses of localized annealing in the making of stripe waveguides are also addressed. This work has evolved from the physics of semi-insulating materials, to optimizing devices, to building complete systems using photorefractive quantum wells. The second has lead to an understanding of the free-carrier grating formation in a HVCSEL and the designing of a HVCSEL with observed diffraction efficiencies as high as 5%.
Degree
Ph.D.
Advisors
Nolte, Purdue University.
Subject Area
Condensation|Materials science|Optics
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