Current aperture vertical electron transistors with ammonia molecular beam epitaxy grown P-type gallium nitride as a current blocking layer
A current aperture vertical electron transistor (CAVET) with ammonia (NH 3 ) based molecular beam epitaxy (MBE) grown p-type Gallium Nitride (p-GaN) as a current blocking layer (CBL). Specifically, the CAVET features an active buried Magnesium (Mg) doped GaN layer for current blocking purposes. This structure is very advantageous for high power switching applications and for any device that requires a buried active p-GaN layer for its functionality.
1. A method of fabricating a current aperture vertical electron transistor (CAVET), comprising:
defining a current aperture region and a sacrificial region in a first III-nitride layer;
removing the first III-nitride layer in the sacrificial region;
forming a III-nitride current blocking layer around the current aperture region;
forming one or more second III-nitride layers on both the first III-nitride layer and the III-nitride current blocking layer; and
electrically connecting a source of the CAVET and the III-nitride current blocking layer such that, during the CAVET's operation, there is no bias between the source and the III-nitride current blocking layer.
2. The method of claim 1 , wherein the III-nitride current blocking layer is grown using ammonia (NH 3 ) based molecular beam epitaxy (MBE).
3. The method of claim 1 , further comprising forming a mask over the current aperture region prior to removing the first III-Nitride layer in the sacrificial region.
4. The method of claim 3 , further comprising removing the mask prior to forming the second III-Nitride layers.
5. The method of claim 1 , wherein:
the III-nitride current blocking layer is grown by a Metal Organic Chemical Vapor Deposition (MOCVD) growth technique by doping a Gallium Nitride layer with Mg dopants,
the III-nitride current blocking layer is activated by annealing in a hydrogen free environment at a temperature above 700° C. to make the III-nitride current blocking layer a p-type III-nitride current blocking layer, and
the second III-nitride layers comprising AlGaN/GaN layers are regrown in ammonia-MBE which does not passivate the Mg acceptors, thereby preserving the p-type behavior of the III-nitride current blocking layer.
6. The method of claim 1 , further comprising:
growing and doping the III-nitride current blocking layer comprising a hole concentration and composition wherein the III-nitride current blocking layer provides a barrier to electron flow, vertically through the III-nitride current blocking layer, in a range of 1-2 electron-Volts.
7. The method of claim 1 , further comprising:
growing and doping the III-nitride current blocking layer comprising a hole concentration and composition wherein the III-nitride current blocking layer provides a barrier to electron flow, vertically through the III-nitride current blocking layer, of at least 2 electron-Volt.
8. The method of claim 1 , further comprising growing and doping the III-nitride current blocking layer to form an active p-type doped III-nitride layer.
9. The method of claim 8 , wherein the III-nitride current blocking layer is an active p-type GaN layer.
10. The method of claim 9 , further comprising doping the III-nitride current blocking layer with Magnesium to form the p-type GaN layer comprising an active Magnesium doped layer.
11. The method of claim 1 , wherein the current aperture region comprises n-type GaN.
12. The method of claim 1 , further comprising:
forming a drain; and
forming an n-type III-nitride drift region between the current aperture region and the drain, wherein an n-type doping concentration in the n-type III-nitride drift region is less than an n-type doping concentration in the current aperture region.
13. The method of claim 1 , further comprising:
forming an active region or channel comprising a two dimensional electron gas confined in a GaN layer by an AlGaN barrier layer;
depositing the source comprising a source contact to the GaN layer and the AlGaN barrier layer;
forming a drift region, comprising one or more n-type GaN layers, wherein the III-nitride current blocking layer is between the drift region and the active region or channel;
depositing a drain contact to the drift region; and
positioning a gate on or above the active region or channel and the current aperture region, to modulate a current between the source contact and the drain contact.
14. The method of claim 13 , further comprising:
selecting a lateral position of the gate above the channel and the current aperture region.
15. The method of claim 14 , further comprising:
selecting a lateral extension of the gate over the channel and the current aperture region to control a peak electric field in the CAVET; and
providing a dielectric layer between the lateral extension and the channel.
16. The method of claim 1 , wherein the current blocking layer causes on-state current to flow through the current aperture region.
17. The method of claim 1 , wherein the III-nitride current blocking layer is such that the CAVET is operable to prevent a current density of greater than 0.4 A/cm 2 from flowing through the current blocking layer when the CAVET is biased in an off state with a source-drain voltage of 400V.
18. The method of claim 1 , wherein the III-nitride current blocking layer surrounds and is all around the current aperture region.
19. The method of claim 1 , further comprising:
forming a mask over the current aperture region;
removing the first III-Nitride layer in the sacrificial region; and
growing a p-type Gallium Nitride (GaN) layer by Metal Organic Chemical Vapor Deposition (MOCVD) and selecting growth conditions wherein no p-type GaN is grown over the mask and the III-nitride current blocking layer, comprising the p-type GaN around the current aperture region, is formed.