Enhancement mode field effect device and the method of production thereof

Abstract

A method is disclosed for producing Group III-N field-effect devices, such as HEMT, MOSHFET, MISHFET or MESFET devices, comprising two active layers, e.g. a GaN/AlGaN layer. The method produces an enhancement mode device of this type, i.e. a normally-off device, by providing a passivation layer on the AlGaN layer, etching a hole in the passivation layer and not in the layers underlying the passivation layer, and depositing the gate contact in the hole, while the source and drain are deposited directly on the passivation layer. The characteristics of the active layers and/or of the gate are chosen such that no two-dimensional electron gas layer is present underneath the gate, when a zero voltage is applied to the gate. A device with this behavior is also disclosed.

What is claimed is: 
     
         1 . A method of fabricating a semiconductor device, the method comprising:
 depositing a first active layer on a substrate;   depositing a second active layer on the first active layer, the second active layer having a higher band-gap than the first active layer;   depositing a passivation layer on the second active layer;   depositing a source electrode and a drain electrode in direct electrical contact with the passivation layer;   etching at least one hole in the passivation layer, the at least one hole being located between the source and drain electrode and not protruding into the layers underlying the passivation layer; and   depositing a gate contact in the hole.   
     
     
         2 . The method according to  claim 1 , wherein
 the second active layer has a composition, thickness and stress such that a two-dimensional electron gas layer is absent between the first active layer and the second active layer, when no additional layers are deposited on the second active layer,   and wherein the passivation layer is applied in such a way and has material characteristics such that a two-dimensional electron gas is created between the first and the second active layer, after deposition of the passivation layer,   and wherein the gate contact is applied in such a way and has material characteristics such that no substantial two-dimensional electron gas layer is present underneath the gate contact when the gate and source contacts are at the same voltage.   
     
     
         3 . The method according to  claim 1 , wherein
 the second active layer has a composition, thickness and stress such that a two-dimensional electron gas layer is present between the first active layer and the second active layer, when no additional layers are deposited on the second active layer,   and wherein the passivation layer is applied in such a way and has material characteristics such that the two-dimensional electron gas layer is enhanced between the first and the second active layer, after deposition of the passivation layer,   and wherein the hole(s) are etched through the complete thickness of the passivation layer,   further comprising plasma treating the parts of the second active layer exposed by the hole, in order to eliminate the two-dimensional electron gas layer in the locations corresponding to the hole.   
     
     
         4 . The method according to  claim 1 , wherein
 the second active layer has a composition, thickness and stress such that a two-dimensional electron gas layer is present between the first active layer and the second active layer, when no additional layers are deposited on the second active layer,   and wherein the passivation layer is applied in such a way and has material characteristics such that the two-dimensional electron gas layer is enhanced between the first and the second active layer, after deposition of the passivation layer,   and wherein the gate contact has a work function so as to eliminate the two-dimensional electron gas layer underneath the hole.   
     
     
         5 . The method according to  claim 1 , further comprising depositing, after etching the hole, a dielectric layer on the second active layer, and wherein the gate contact is deposited on the dielectric layer. 
     
     
         6 . The method according to  claim 1 , wherein the passivation layer is deposited in-situ on the second active layer. 
     
     
         7 . The method according to  claim 1 , wherein the first active layer, the second active layer, and the passivation layer are deposited by Metal Organic Chemical Vapor Deposition growth (MOCVD).