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Integration of single-crystal devices with flexible substrates using conductive adhesive layers


Flexibility is a desirable attribute for many large-area semiconductor devices such as light-emitting diodes, photodetectors, and solar cells. Plastic substrates have received considerable attention for flexible devices due to their combination of chemical resistance, toughness, and low cost. However, in cases where monocrystalline semiconductor material is desired, integrating the semiconductor with the plastic in a manner that allows backside conduction can be challenging due to processing constraints of the plastic. This thesis discusses the integration of flexible single-crystal semiconductors with plastic substrates utilizing conductive intermediary adhesive materials. Various methods are discussed for the attainment of the thin semiconductor layer to be bonded. In particular, backside etching is evaluated in the isolation of thin GaAsP and Si for double and single-flip processes, and commercially-available ultra-thin Si wafers are evaluated for pre-thinned diode fabrication. Silver colloid-filled epoxy and double-sided tape are studied for the integration of these materials to polyethylene naphthalate substrates, and compared to selected metal intermediary bonding schemes. Fabricated and evaluated are thin flexible light-emitting diodes and Si-Pd Schottky diodes. Additionally, an accelerated lifetime test is applied to the adhesives to estimate their long-term stability. Finally, regular segmentation is investigated as a method to introduce effective flexibility to thick wafers. The technique is applied to ̃400[mu]m-thick InP- based multiple-quantum-well solar cells, and the effects of the segmentation are analyzed

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