Graphene-on-semiconductor substrates for analog electronics
Electrically conductive material structures, analog electronic devices incorporating the structures and methods for making the structures are provided. The structures include a layer of graphene on a semiconductor substrate. The graphene layer and the substrate are separated by an interfacial region that promotes transfer of charge carriers from the surface of the substrate to the graphene.
1. An electrically conductive structure comprising:
a substrate comprising a layer of germanium;
a layer of graphene;
an interface region comprising sub-stoichiometric germanium oxides and germanium dioxide separating the layer of germanium from the layer of graphene, wherein the interface region provides surface energy states lying within the fundamental energy bandgap of the germanium and having energy levels above the Fermi level of graphene, and further wherein the graphene is doped with electrons from the surface energy states.
2. The structure of claim 1 , wherein the layer of germanium has a thickness of no greater than 10 μm.
3. The structure of claim 2 , wherein the germanium substrate comprises n-doped germanium having an n-type dopant concentration of no greater than 1×10 17 cm −3 at 300 K.
4. The structure of claim 1 , wherein the germanium substrate comprises n-doped germanium having an n-type dopant concentration of no greater than 1×10 16 cm −3 at 300 K.
5. The structure of claim 1 , wherein the sheet resistance in the layer of graphene is no greater than 1000Ω at 300 K.
6. The structure of claim 5 , wherein the sheet resistance in the layer of graphene is no greater than 100Ω at 300 K.
7. The structure of claim 1 , wherein the interface region has a thickness of no greater than 10 nm.
8. The structure of claim 7 , wherein the interface region has a thickness in the range from 2 nm to 10 nm.
9. The structure of claim 1 , wherein the layer of graphene is a single sheet of graphene.
10. The structure of claim 1 , wherein the layer of germanium is disposed on a layer of silicon.
11. A field effect transistor comprising:
a source electrode;
a drain electrode;
gate electrode;
a conducting channel in electrical contact with the source electrode and the drain electrode, the conducting channel comprising a layer of graphene;
a germanium capping layer disposed over the conducting channel;
a gate dielectric disposed between the gate electrode and the germanium capping layer;
a germanium substrate; and
an interface region separating the germanium substrate from the layer of graphene, the interface region comprising sub-stoichiometric germanium oxides and germanium dioxide;
wherein the sub-stoichiometric germanium oxides and germanium dioxide produce energy states within the fundamental energy bandgap of the germanium and further wherein charge carriers occupying the energy states transfer to the graphene at room temperature to provide mobile charge carriers in the graphene.
12. A method of making an electrically conductive structure, the method comprising transferring a graphene sheet onto a surface of a graphene substrate in an aqueous environment, the surface having a layer of sub-stoichiometric germanium oxide; wherein an interface region forms between the surface of the germanium substrate and the graphene sheet, the interface region comprising germanium dioxide and water-insoluble, sub-stoichiometric germanium oxides.