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Gallium Nitride processing for high-power and high-frequency devices

Gallium Nitride (GaN) and its related AlxGa1-xN ternary alloys have excellent properties (like a wide band gap, a high critical electric field and a high electron saturation velocity) making them suitable semiconductors for high power and high frequency devices. In particular, due to the presence of the two dimensional electron gas (2DEG) generated by the spontaneous and piezoelectric polarization charges, AlGaN/GaN heterostructures can be used for the fabrication of high electron mobility transistors (HEMTs).


(a) Surface morphology of an AlGaN/GaN heterostructure grown on Si; (b) Carrier concentration profile determined by C-V analysis .

The research activity carried out at IMM Catania headquarters is focused on fundamental aspects related to lateral and vertical GaN-based devices, i.e., spanning from the development and characterization of the elementary device building blocks (contacts, gate dielectrics, etc.), to their integration and impact into the device behavior, considering also the role of the material quality. The involved team holds a multidisciplinary background (physics, chemistry, electronic engineering and material science) and expertise on GaN materials and devices.

The work is performed on a variety of substrates including large-area Si, SiC, and sapphire, with a view towards “free-standing” GaN for novel vertical devices concepts. The incoming GaN-based epilayers and AlGaN/GaN heterostructures are characterized in terms surface morphology, electrically active dislocations density, sheet carrier density and mobility of the 2DEG, etc. The activity includes not only the physical characterization of materials and processes, but also the  fabrication of devices and test patterns (i.e., Schottky, MIS capacitors, TLM and VdP, HEMTs, MISHEMTs, ...) for advanced electrical analyses.


(a) I–V characteristics of normally-off p-GaN/AlGaN/GaN HEMT devices employing a a non-annealed metal gate. (b) Schematic cross section of the device; (c) TEM cross section of the gate region [IEEE Transactions on Electron Dev. 63, 2735 (2016)].


(a) Temperature dependence of the peak field effect mobility in recessed hybrid normally-off SiO2/GaN MISHEMT (b) Schematic cross section of the device; (c) AFM image taken in the recessed gate region of the MISHEMT [IEEE Transactions on Electron Dev. 64, 2896 (2017)].

In the last years, extensive studies on contact technology and normally-off HEMTs with a p-GaN gate have been carried out. Moreover, the conduction mechanisms and trapping phenomena in recessed hybrid MISHEMTs have been investigated. Activity on the synthesis, characterization and integration of dielectrics and nano-laminates by ALD is also carried out to limit gate leakage and current collapse effects in GaN devices.

The group has several national and international collaborations with industrial and academic institutions, developed in the last years through the participation in National and European research programs: Ambition Power (2010-2014), Last Power (2010-2014), GraNitE (2016-2019), ETNA - Cooperation Agreement CNR-PAS (2017-2019).

 

Reference person: Fabrizio Roccaforte

Involved personnel:  Giuseppe Greco, Patrick Fiorenza, Filippo Giannazzo, Raffaella Lo Nigro,  Salvatore Di Franco, Domenico Corso, Emanuela Schilirò, Monia Spera, Fabrizio Roccaforte

Power and High Frequencies Devices

Research Topics