Gallium nitride based diodes with low forward voltage and low reverse current operation
View Patent ↗New Group III based diodes are disclosed having a low on state voltage (V f ) and structures to keep reverse current (I rev ) relatively low. One embodiment of the invention is Schottky barrier diode made from the GaN material system in which the Fermi level (or surface potential) of is not pinned. The barrier potential at the metal-to-semiconductor junction varies depending on the type of metal used and using particular metals lowers the diode's Schottky barrier potential and results in a V f in the range of 0.1-0.3V. In another embodiment a trench structure is formed on the Schottky diodes semiconductor material to reduce reverse leakage current. and comprises a number of parallel, equally spaced trenches with mesa regions between adjacent trenches. A third embodiment of the invention provides a GaN tunnel diode with a low V f resulting from the tunneling of electrons through the barrier potential, instead of over it. This embodiment can also have a trench structure to reduce reverse leakage current.
1. A tunneling diode comprising:
an n+ doped Group-III nitride semiconductor layer;
an n− doped Group-III nitride semiconductor layer adjacent to a first side of said n+ doped layer;
a Group-III nitride semiconductor barrier layer on said n− doped layer, with no semiconductor layers between said barrier layer and said n− doped layer,
wherein an exposed portion of the surface of said first side of said n+ doped layer is not covered by said n− doped layer and said barrier layer;
at least one ohmic contact on said exposed portion of said n+ doped layer;
a metal layer on said barrier layer,
said n+ doped, n− doped and barrier layers made from a material system having a piezoelectric stress, said piezoelectric stress related to the thickness of said barrier layer and causing said diode's on-state threshold voltage to be low as a result of enhanced electron tunneling through the potential barrier under forward bias; and
wherein said layers are arranged in the following order: said n+ doped layer, said n− doped layer, said barrier layer, followed by said metal layer.
2. The diode of claim 1 , wherein a portion of said piezoelectric stress localized in said barrier layer provides piezoelectric dipoles having electrons available for conduction to lower the diode's on-state threshold voltage by enhancing electron tunneling.
3. The diode of claim 1 , wherein the number of said piezoelectric dipoles increases as the thickness of said barrier layer increases, while still allowing tunneling currents.
4. The diode of claim 1 , further comprising a substrate adjacent to said n+ doped layer opposite said n− doped layer, said substrate comprising sapphire, silicon carbide or silicon.
5. The diode of claim 1 , wherein said n+ doped layer, n− doped layer and barrier layer comprise polar materials.
6. The diode of claim 1 , wherein said n+ doped layer, n− doped layer and barrier layer are from the Group III nitride material system.
7. The diode of claim 1 , wherein said n+ doped layer is GaN, said n− doped layer is GaN, and said barrier layer is AlGaN.
8. The diode of claim 1 , wherein said n+ doped layer, said n− doped layer and barrier layer are formed from polar materials.
9. The diode of claim 1 , wherein said n+ doped layer, n− doped layer and barrier layer are formed from complex polar oxides.
10. The diode of claim 9 , wherein said complex polar oxides comprise materials from the group consisting of strontium titanate, lithium niobate, lead zirconium titanate, or combinations thereof.
11. The diode of claim 1 , wherein said n+ doped layer, n− doped layer and barrier layer are formed from binary polar oxides.
12. The diode of claim 11 , wherein said binary polar oxides comprise zinc oxide.
13. The diode of claim 1 , further comprising a trench structure in said barrier and n− doped layers, said diode experiencing a reverse leakage current under reverse bias, said trench structure reducing the amount of said reverse leakage current.
14. The diode of claim 13 , wherein said trench structure comprises a plurality of trenches in said barrier and said n− layers having mesa regions between adjacent trenches, each of said trenches having opposing sidewalls and a bottom surface, said sidewalls and bottom surface of each of said trenches being coated by a layer of insulating material, said metal layer covering each of said trench's layer of insulating material and said mesa regions, so that each said layer of insulating material is sandwiched between said metal layer and its respective said sidewalls and bottom surface.
15. The diode of claim 14 , wherein a portion of said insulating material is replaced by a metal with a high work function, said metal with a high work function being separated from said metal layer by said insulating material.
16. A tunneling diode comprising:
an n+ doped nitride semiconductor layer;
an n− doped nitride semiconductor layer adjacent to a first side of said n+ doped layer;
a barrier layer on said n− doped layer, with no semiconductor layers between said barrier layer and said n− doped layer,
wherein an exposed portion of the surface of said first side of said n+ doped layer is not covered by said n− doped layer and said barrier layer;
at least one ohmic contact on said exposed portion of said n+ doped layer;
a metal layer on said barrier layer,
said n− doped nitride layer forming a junction with said barrier layer, said junction having a potential barrier, said barrier layer having a spontaneous and piezoelectric polarization that results in dipoles having electrons available for conduction which causes said diode's on-state threshold voltage to be low as a result of electron tunneling through the potential barrier under forward bias; and
wherein said layers are arranged in the following order: said n+ doped layer, said n− doped layer, said barrier layer, followed by said metal layer.