2D Hexagonal Boron Nitride Based Processes For Flexible Electronics
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Gujrati, Rajat
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Abstract
This thesis focuses on advancing the field of flexible electronic devices by utilizing two-dimensional hexagonal boron nitride (2D h-BN) as a release layer. The methodology used in the thesis is the selective area growth (SAG) of III-N materials through quasi van der Waals (vdW) epitaxy on 2D h-BN. This approach is adopted to address and solve the state-of-the-art challenges associated with InGaN/GaN solar cells and micro-light emitting diodes (micro-LEDs).
The pathway to achieving efficient InGaN/GaN solar cells is impeded by
degradation of the crystalline quality of the InGaN layer beyond a certain critical thickness, the phase separation of InGaN alloy at the high indium content in it, and the presence of
the strong polarization charges at the InGaN/GaN hetero-interface. To overcome these challenges we propose a novel design of InGaN/GaN solar cells which includes conformally grown p-GaN, by MBE at low temperature, on top of an InGaN Nano Pyramid (NP) absorber, grown by nano SAG. Further, by coupling this structure with the quasi van der Waals epitaxy on 2D h-BN, two new designs of solar cells (a) conformal NP on
copper, and (b) free-standing NP, are proposed. The performance of these solar cells is evaluated by optical and electrical simulations and a complete fabrication process of these
solar cells is presented.
The primary challenge for micro-LED fabrication has been the lowered
performance of tiny micro-LEDs caused by chemical etching that defines individual LEDs and the complexity and cost associated with the lift-off and transfer of these LEDs from sapphire substrates to suitable supports. In this thesis, for the first time, we report a demonstration of coupled vdW epitaxy and SAG, to fabricate micro-LEDs of various shapes down to ultra-tiny sizes of 1.4 microns. The selective area growth of multi-quantum wells LED heterostructures allows to obtain ultra smooth crystalline sidewalls and vdW epitaxy of 2D h-BN allows simple lift-off and transfer of micro-LEDs. We perform a complete fabrication process of micro-LEDs and its transfer to a flexible copper substrate. Finally, device performances of these high-brightness micro-LEDs are reported.
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Date
2023-07-25
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Dissertation