Fabrication and Characterization of Graphene Heterostructures with Nitride Semiconductors for High Frequency Vertical Transistors

Abstract

The hot electron transistor (HET) is an unipolar majority carrier vertical device with great potential for high frequency (THz) applications. Recently, graphene (Gr) heterostructures with Nitrides have been considered as a promising material system to implement this device concept, with GaN/AlGaN (or GaN/AlN) working as emitter/emitter‐base barrier and Gr as the ultrathin base enabling ballistic transit of hot electrons. In this work, the main issues related to the fabrication of Gr/Nitrides heterojunctions are discussed. An optimized transfer procedure of large‐area Gr membranes onto AlGaN/GaN grown on Si(111) is illustrated. In particular, a soft O2 plasma pretreatment of the AlGaN surface is found to greatly improve the Gr adhesion, resulting in a reduced cracks density. A nanoscale electrical characterization of the obtained Gr/AlGaN/GaN heterostructures was carried out by conductive atomic force microscopy, to evaluate the effect of typical nanometric corrugations (wrinkles) of the Gr membrane on the current transport. These morphological features introduce resistive contributions both to the lateral current transport in the Gr membrane and to the vertical current injection across the heterojunction. The impact of these results on the relevant electrical parameters (i.e., the base resistance and the emitter‐base injection efficiency) of a HET based on this heterostructure is also discussed.

Conductive Atomic Force Microscopy of Semiconducting Transition Metal Dichalcogenides and Heterostructures

“…In the last years, the integration of graphene and semiconducting TMDs with silicon and other semiconductors, such as GaN and related materials [94], has been explored by several research groups. Different approaches have been explored, from the transfer of 2D materials [95][96][97][98] to the direct growth on the semiconductor substrate [19,99]. In particular, the epitaxial growth of MoS 2 on the basal plane of GaN is especially favored by the low in-plane lattice mismatch (<1%) between the two hexagonal crystals.…”

Extensive Fermi‐Level Engineering for Graphene through the Interaction with Aluminum Nitrides and Oxides

“…The growth or the transfer of graphene on these substrates could further enhance their features, allowing for a high‐frequency modulation of the electrical current, e.g., in vertical heterostructural transistors . However, even if the first experimental steps have been made toward such a direction, theoretical studies that explore the structural and electronic properties of these systems are largely missing. In this study, we use the density functional theory (DFT) to study the properties of single‐layer graphene on AlN (0001) and (000‐1) surfaces, considering both ideal and reconstructed terminations.…”

Vertical Transistors Based on 2D Materials: Status and Prospects

“…These have been used for the fabrication of device arrays using semiconductor fab-compatible approaches. As an example, Gr junctions with AlGaN/GaN heterostructures showing excellent lateral uniformity have been reported [100,110] and are currently investigated as building blocks for HET devices. Figure 10a,b reports two representative morphologies of the AlGaN surface without (a) and with (b) a single-layer Gr membrane on top.…”