Boron Nitride Growth and Electronics
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With the rise of 2D materials in the past decade there has been an increasing need for an appropriate insulator within the family in order to fabricate well behaved 2D based transistors. Hexagonal Boron Nitride (hBN) has fulfilled that need by providing a substrate free of dangling bonds, low levels of corrugation and excellent thermal and chemical stability. However, hBN itself is quite an intriguing material and has been somewhat neglected within the 2D family. Its wide bandgap allows for DUV emission in the UVC range which is critical for water sanitation and biological and chemical process’. It has also been shown to host photoactive defects which can emit single photons paving the way for the creation of solid state single photon emitters, something that has proven impossible until now. Due to these reasons it’s imperative that fundamental research into hBN’s synthesis as well as its electronic and optical properties be conducted. With regards to the growth of hBN our main focus is on the popular CVD method, however, recently other methods are also underway (MBE, LPE, etc…). In this regard, hBN growth has lagged Graphene (Gr) where millimeter (mm) sized single crystals have already been demonstrated. We show that this feat can also be accomplished in hBN through a variety of optimization schemes where single crystals up to 0.3mm where synthesized. We also focus on the proposed growth mechanisms and difficulties of growing thick layered hBN via CVD. With regards to its electronic properties we report the demonstration of high mobility devices where our CVD grown hBN was used as the conductive channel. This is unprecedented in the scheme of 2D’s since hBN has been widely regarded to be insulating. We explore the possible doping mechanisms in our grown films and also give possible reasons why our material is conductive while the exfoliated films used by the majority of researchers in the field are not. Finally, we note that our work is only the beginning of what may be an incredibly exciting field of transport in wide band-gap 2D materials since 2D GaN has also recently synthesized which possesses a bandgap similar to hBN. We are also only the first of very few reports of large single crystal hBN films and hope that this will open the doors to studying the high-quality growth of hBN monolayers and multilayers similar to what happened with Gr. The field of 2D materials would greatly benefit from the wide availability of high quality large single crystal hBN, since this would avoid grain boundaries and other defects in hBN that would degrade its use as a substrate.
CVD Growth; Hexagonal Boron Nitride; Space Charge Transport; Electrical engineering; 2D materials
Spencer, Michael G.
Rana, Farhan; McEuen, Paul L.
Electrical and Computer Engineering
Ph. D., Electrical and Computer Engineering
Doctor of Philosophy
dissertation or thesis