Joint research project

GHOST II: Graphene Heterostructures with ultra-thin films Of Nitride SemiconducTors for advanced electronics

Project leaders
Filippo Giannazzo, Bela Pecz
UNGHERIA - HAS (MTA) - Accademia Ungherese delle Scienze
CNR/HAS triennio 2019-2021 2019-2021
Physical sciences and technologies of matter
Thematic area
Physical sciences and technologies of matter
Status of the project
Report for renewal

Research proposal

Group III-Nitride semiconductors (III-N), i.e. GaN, InN, AlN and their alloys, are strategic materials for optoelectronics, high-power and high-frequency electronics. Recently, the integration of graphene (Gr) with III-N has been the object of increasing scientific interests, as it can lead to huge improvements of the state-of-the-art III-N technology (HEMTs, LEDs,..), and open the way to novel device concepts for high frequency electronics [1]. Of course, integrating Gr with III-N and fabricating devices based on these systems implies many challenges. Some of them have been addressed by IMM and MFA during the GHOST project 2016-2018.
The main topic of GHOST was the growth and characterization of Gr heterostructures with ultra-thin films of III-N. Samples preparation was carried out at Linkoping University (LiU), in the framework of the European project GRIFONE involving IMM and MFA as partners. In particular, IMM and MFA worked on the nano- and atomic scale structural/chemical and electrical characterization of these heterostructures, employing the advanced characterization techniques (electrical AFM and high resolution TEM) available in their laboratories. Ad-hoc sample preparation protocols and measurements procedures were developed in close collaboration between the two groups to analyze these critical samples. During the project, MFA acquired a new atomic resolution TEM, and samples produced in the GHOST project served for the validation of this new instrumentation. A collaboration between MFA and the TEM group at IMM, hosting a new generation aberration corrected STEM, was also established during the project, with the aim to make comparative evaluations on the capabilities of these two state-of-the-art equipment using such critical samples.
One of the main achievements of GHOST was the demonstration that stable ultra-thin films of III-N can be obtained by intercalation of the group III (e.g., In, Ga, Al) and N species at the interface between epitaxial Gr and SiC(0001). These observations have been further confirmed by other research groups [2].
Besides the above discussed intercalation procedure, alternative approaches were explored during the GHOST project for the fabrication of Gr/III-N junctions. In particular, an optimized transfer procedure of Gr (grown by CVD on Cu) to the surface of Al(Ga)N/GaN heterostructures was developed at IMM. These activities were carried out in collaboration with leading European groups in III-N materials growth (CNRS-CRHEA in France and UNIPRESS in Poland). Furthermore, some key process steps for the fabrication of devices based on Gr/III-N heterostructures were also investigated. These included:
- the growth of thin AlN films on GaN by low temperature plasma-assisted atomic layer deposition (ALD);
- the deposition of thin films of high-k dielectrics onto Gr by thermal ALD with an "in-situ" seeding layer;
- the fabrication of Schottky contacts onto bulk GaN.
The GHOST project already resulted in joint publications in peer-reviewed journals (among which an invited feature article [1]) and other papers are in preparation. Several contributions have been presented in international conferences (among which 5 invited talks).
Finally, two of the project's partners, G. Greco (IMM) and B. Pecz (MFA) are organizers of the Symp R "New frontiers in wide-bandgap semiconductors and heterostructures for electronics, optoelectronics and sensing" at EMRS Fall 2018 in Warsaw.
The new GHOST II project will further extend the above discussed activities, focusing on the development of novel electronic device concepts based on Gr/III-N heterostructures.
The studies on the intercalation of InN and GaN ultra-thin films at epitaxial Gr/SiC(0001) interface will be continued, in collaboration with LiU. IMM will employ conductive AFM to investigate current injection mechanisms across the Gr/III-N/SiC interface. The relevant electrical parameters of the heterostructures, e.g. Gr/III-N and III-N/SiC band alignment will be extracted by modelling local current-voltage characteristics. Furthermore, MFA and IMM will employ the complementary TEM and STEM equipment available in the respective laboratories, to perform the structural/chemical/spectroscopic characterization of these ultrathin layers. These investigations will be aimed to shed light on the relation between intercalation conditions and crystalline structure of the ultrathin III-N layers, clarifying when 2D layers with hexagonal structure can be obtained, instead of those with the conventional wurzite structure. Atomic resolution electron spectroscopy techniques (EELS, EDS) will be employed to investigate the chemical composition as well as the bandgap of these layers. Some of the advanced electron microscopy experiments will be carried out in the framework of a recently funded ESTEEM 3 project.
Novel device concepts for advanced electronics applications (ultra-high frequency and low power dissipation) will be developed within the GHOST II project. In particular Gr/Al(Ga)N/GaN or Gr/III-N/SiC heterostructures will be employed to realize a Hot Electron Transistor, a vertical device where monolayer Gr works as ultra-thin base electrode, enabling ballistic transit of hot electrons injected from the emitter (GaN or SiC) through the AlGaN barrier layer. The fabrication of test structures (capacitors, diodes, van der Pauw) and of the final device prototypes will be carried out within IMM clean room. IMM will work also on the electrical characterization, both at device level and at nanoscale, in order to elucidate the mechanisms of current transport at the interfaces. MFA will carry out high resolution TEM characterization on the cross sections of individual device structures prepared by the FIB technique using low energy ion beams.
[1] F. Giannazzo, G. Fisichella, G. Greco, A. La Magna, F. Roccaforte, B. Pecz, et al., Phys. Status Solidi A 214, 1600460 (2017).
[2] Z. Y. Al Balushi, et al., Nature Mat. 15, 1166-1173 (2016).

Research goals

- High resolution structural, chemical and electrical characterization of Gr heterostructures with ultra-thin films of Nitride semiconductors (InN, GaN, AlN), fabricated by intercalation of group III and N atoms at the interface between epitaxial Gr and SiC(0001).

- Development of novel device concepts, such as the hot electron transistor, based on Gr/Al(Ga)N/GaN or Gr/III-N/SiC heterostructures.

- Training of young-researchers:
From the Hungarian side, Dr. Ildiko Cora is a young post-doc (Ph.D. awarded in 2013)
From the Italian side, Dr. Emanuela Schilirò is a young post-doc (PhD awarded in 2017). Furthermore, Monia Spera, a PhD student of the University of Catania, working at CNR-IMM, will be involved in the project's activities.

- Joint dissemination activities:
Scientific publications (at least 4) in high IF journals, such as ACS Appl. Materials & Interfaces, Carbon, Nanotechnology, PRB, APL,...
Participation in specialized international conferences (at least 4), such us Graphene Week, Graphene, ICSCRM/ECSCRM, ICNS,..
Organization of a workshop and/or proposal of a Symposium for EMRS Spring/Fall meeting 2021 on the topic of "Growth and advanced characterization of 2D materials heterostructures".
Organization of dedicated seminars with industries (such as STMicrolectronics) to illustrate the potentialities of the investigated heterostructures for electronics, sensing,..
Submission of H2020 project proposals involving CNR-IMM and HAS-MFA and other EU partners.

Last update: 17/07/2024