Low-temperature self-limiting growth of nitride materials via ALD necessitates the usage of an external energy source, which will create nitrogen radicals to be incorporated within the film. RF plasma sources of various architectures are commonly used for this purpose. As opposed to conventional ALD materials, i.e., oxides where oxygen is a co-reactant, for nitrides it is one of the most important impurity who kills the crystal quality of nitride films. Therefore, leak-free vacuum systems with UHV-grade base vacuum levels are needed. Moreover, even the very plasma source material itself might become an oxygen contamination source.
In our lab, we have demonstrated that using a stainless-steel based capacitively-coupled hollow-cathode plasma source helps to reduce the oxygen impurity level in GaN films by orders of magnitude [JMC 2014]. By thorough growth optimization, we achieved self-limiting deposition recipes for crystalline hegzagonal GaN, AlN, and InN films and their ternary alloys [JMC 2015, AIP Adv 2016, JVSTA 2015/2016]. We successfully have shown that the entire III-nitride material family can be grown at a common substrate temperature as low as 200°C. Efforts to achieve near-single crystal quality material is ongoing.
This initial achievement might pave the way for III-nitride based flexible (opto)electronics, as it features several inherent advantages with respect to conventional oxide-based technology. In collaboration with Prof. Ali Kemal Okyay’s research group, we have demonstrated ALD-grown GaN-channel thin-film transistors and GaN-absorption layer UV photodetectors as proof-of-concept device applications [APL 2014, JVSTA 2015].
BIYIKLI RESEARCH GROUP 