We report on optimisation of the environmental stability and high temperature operation of surface transfer doping in hydrogen-terminated diamond using MoO3 and V2O5 surface acceptor layers. In-situ annealing of the hydrogenated diamond surface at 400 °C was found to be crucial to enhance long-term doping stability. High temperature sheet resistance measurements up to 300 °C were performed to examine doping thermal stability. Exposure of MoO3 and V2O5 transfer-doped hydrogen-terminated diamond samples up to a temperature of 300 °C in ambient air showed significant and irreversible loss in surface conductivity. Thermal stability was found to improve dramatically however when similar thermal treatment was performed in vacuum or in ambient air when the oxide layers were encapsulated with a protective layer of hydrogen silsesquioxane (HSQ). Inspection of the films by X-ray diffraction revealed greater crystallisation of the MoO3 layers following thermal treatment in ambient air compared to the V2O5 films which appeared to remain amorphous. These results suggest that proper encapsulation and passivation of these oxide materials as surface acceptor layers on hydrogen-terminated diamond is essential to maximise their environmental and thermal stability.

We report a first-principles study of the structural and electronic properties of two-dimensional (2D) layer/hydrogen-terminated diamond (100) heterostructures. Both the 2D layers exhibit weak van-der-Waals (vdW) interactions and develop rippled configurations with the H-diamond (100) substrate to compensate for the induced strain. The adhesion energy of the hexagonal boron nitride (hBN) layer is slightly higher, and it exhibits a higher degree of rippling compared to the graphene layer. A charge transfer analysis reveals a small amount of charge transfer from the H-diamond (100) surface to the 2D layers, and most of the transferred charge was found to be confined within the vdW gap. In the graphene/H-diamond (100) heterostructure, the semi-metallic characteristic of the graphene layer is preserved. On the other hand, the hBN/H-diamond (100) heterostructure shows semiconducting characteristics with an indirect bandgap of 3.55 eV, where the hBN layer forms a Type-II band alignment with the H-diamond (100) surface. The resultant conduction band offset and valence band offset are 0.10 eV and 1.38 eV, respectively. A thin layer of hBN offers a defect-free interface with the H-diamond (100) surface and provides a layer-dependent tunability of electronic properties and band alignment for surface-doped diamond field effect transistors.

We report on the fabrication and measurement of hydrogen-terminated diamond field-effect transistors (FETs) incorporating V 2 O 5 as a surface acceptor material to induce transfer doping. Comparing a range of gate lengths down to 50 nm, we observe inversely scaling peak output current and transconductance. Devices exhibited a peak drain current of ∼700 mA/mm and a peak transconductance of ∼150 mS/mm, some of the highest reported thus far for a diamond metal semiconductor FET (MESFET). Reduced sheet resistance of the diamond surface after V 2 O 5 deposition was verified by four probe measurement. These results show great potential for improvement of diamond FET devices through scaling of critical dimensions and adoption of robust transition metal oxides such as V 2 O 5 . Index Terms-2-D hole gas (2DHG), diamond metal semiconductor field-effect transistor (MESFET), drain-induced barrier lowering (DIBL), electronic devices, gate length, power, radio frequency (RF), surface transfer doping, V 2 O 5 .

The epitaxial growth of thin (∼20–40 nm) Si buffer layer on Si(110) leads to the formation of ∼100-nm-wide, uniformly sized faceted pits. The cause of these rhombohedral pits is revealed to be the overgrowth of a homoepitaxial layer over clusters of coherent contaminant particles, possibly SiC. Deposition of Ge on such “pitted” surfaces shows highly selective nucleation of pairs of coherent islands at the opposite corners of the pits along the 〈110〉 direction. Continued deposition leads to strain relaxation of one or both of the islands within the pit which then rapidly coarsen to form a single Ge island within the pit. Our observations offer insight into heterogeneous nucleation mechanisms important for producing controlled arrays of self-assembled quantum dots.

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