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Enabling direct use of control spalled substrates through fracture control and planarizing overgrowth via hydride vapor phase epitaxy
Braun, Anna K.
Braun, Anna K.
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2023
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2024-10-18
Abstract
Controlled spalling is a promising low-cost substrate reuse technique for epitaxial growth
substrates; however, the spalling fracture produces large facets on (100)-oriented GaAs because
the fracture is constrained to low-energy planes that are oriented at a high degree to the substrate
surface. This facet formation has so far made spalling GaAs infeasible for wafer reuse without
costly polishing steps. This thesis demonstrates control of the fracture behavior and planarizing
overgrowth that may enable use of spalled GaAs substrates without surface repreparation.
First, design rules are developed for nanoimprint lithography patterned interlayers to enable
facet suppression. We demonstrate facet suppression using a pattern that follows these design
rules, resulting in a surface that is potentially suitable for growth without polishing. Next, the
dependence of the faceting behavior on spall direction, substrate orientation (including (100),
(110) and (211)), and offcut is investigated. We develop an equation to describe the excess surface
area produced via faceting and use it to show that low-energy planes available in the spall
direction will support faceting when the surface energy scaled by the excess surface created does
not exceed the fracture energy parallel to the substrate surface. Facet free surfaces are achieved
on (110) and (211)-oriented substrates, however, we observe offcut and spall direction effects on
the stability of the fracture along the flat plane. Finally, planarizing overgrowth via hydride vapor
phase epitaxy (HVPE) is studied to determine growth conditions that may enable in situ
planarization of GaAs facets. A screening design analysis is used to efficiently probe the complex
parameter space and we show that high GaCl and low AsH3 partial pressure are favorable for
planarization. We then determine the governing growth mechanisms for planarization and
demonstrate device-quality growth directly on a spalled substrate.
This thesis shows that these techniques have significant promise for enabling controlled
spalling as a low-cost substrate reuse technique. The studies of fracture control also show
behaviors that have not been previously reported or characterized, and the studies of growth rate
anisotropy in HVPE give insight to the difference in growth on different planes and build a
foundation for growth morphology control on any surface.
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