Gallium nitride-based devices and manufacturing process

Abstract

A nitride semiconductor is grown on a silicon substrate by depositing a few mono-layers of aluminum to protect the silicon substrate from ammonia used during the growth process, and then forming a nucleation layer from aluminum nitride and a buffer structure including multiple superlattices of Al R Ga (1-R) N semiconductors having different compositions and an intermediate layer of GaN or other Ga-rich nitride semiconductor. The resulting structure has superior crystal quality. The silicon substrate used in epitaxial growth is removed before completion of the device so as to provide superior electrical properties in devices such as high-electron mobility transistors.

1 . A method of making a semiconductor structure comprising the steps of: 
 (a) depositing aluminum directly on a surface of a silicon substrate to provide an aluminum-protected substrate; then    (b) depositing a nucleation layer of a nitride semiconductor on said aluminum-protected substrate; then    (c) epitaxially growing a buffer structure including one or more superlattices of nitride semiconductors on said nucleation layer; and then    (d) epitaxially growing an operative structure including one or more gallium nitride-based semiconductors on said buffer structure.    
     
     
         2 . A method as claimed in  claim 1  wherein said step of depositing said nucleation layer of said nitride semiconductor includes using NH 3  as a reactant in contact with said aluminum-protected substrate.  
     
     
         3 . A method as claimed in  claim 2  wherein said step of depositing said nucleation layer includes metal organic chemical vapor deposition.  
     
     
         4 . A method as claimed in  claim 1  wherein said step of growing said buffer structure includes growing a first superlattice of nitride semiconductors directly on said nucleation layer.  
     
     
         5 . A method as claimed in  claim 1  wherein said step of epitaxially growing said operative structure includes growing a first layer of nitride semiconductor; said method further comprising depositing at least one first metal layer on said first layer of nitride semiconductor to form a Schottky contact therewith.  
     
     
         6 . A method as claimed in  claim 5  wherein said first layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         7 . A method as claimed in  claim 5  wherein said first layer of nitride semiconductor includes GaN.  
     
     
         8 . A method as claimed in  claim 5  further comprising depositing at least one further metal layer on another surface of said silicon substrate to form an ohmic contact therewith.  
     
     
         9 . A method as claimed in  claim 5  wherein said step of epitaxially growing said operative structure includes growing a further layer of nitride semiconductor atop said buffer structure prior to growing said first layer of nitride semiconductor such that said further layer of nitride semiconductor has a higher doping concentration than that of said first layer of nitride semiconductor.  
     
     
         10 . A method as claimed in  claim 9  wherein said further layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         11 . A method as claimed in  claim 9  wherein said further layer of nitride semiconductor includes GaN.  
     
     
         12 . A method as claimed in  claim 5  further comprising removing a portion of said first layer of nitride semiconductor such that said first layer of nitride semiconductor forms a mesa structure.  
     
     
         13 . A method of making a semiconductor structure comprising the steps of: 
 (a) depositing a nucleation layer of a nitride semiconductor on a silicon substrate; then    (b) epitaxially growing a buffer structure including one or more superlattices of nitride semiconductors on said nucleation layer, said step of growing said buffer structure including growing a first superlattice of nitride semiconductors directly on said nucleation layer; and then    (c) epitaxially growing an operative structure including one or more gallium nitride-based semiconductors on said buffer structure.    
     
     
         14 . A method as claimed in  claim 13  wherein said step of growing said buffer structure includes growing an intermediate layer of a gallium-nitride semiconductor over said first superlattice and growing a second superlattice of nitride semiconductors over said intermediate layer.  
     
     
         15 . A method as claimed in  claim 13  wherein said step of epitaxially growing said operative structure includes growing a first layer of nitride semiconductor; said method further comprising depositing at least one first metal layer on said first layer of nitride semiconductor to form a Schottky contact therewith.  
     
     
         16 . A method as claimed in  claim 15  wherein said first layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         17 . A method as claimed in  claim 15  wherein said first layer of nitride semiconductor includes GaN.  
     
     
         18 . A method as claimed in  claim 15  further comprising depositing at least one further metal layer on another surface of said silicon substrate to form an ohmic contact therewith.  
     
     
         19 . A method as claimed in  claim 15  wherein said step of epitaxially growing said operative structure includes growing a further layer of nitride semiconductor atop said buffer structure prior to growing said first layer of nitride semiconductor such that said further layer of nitride semiconductor has a higher doping concentration than that of said first layer of nitride semiconductor.  
     
     
         20 . A method as claimed in  claim 19  wherein said further layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         21 . A method as claimed in  claim 19  wherein said further layer of nitride semiconductor includes GaN.  
     
     
         22 . A method as claimed in  claim 15  further comprising removing a portion of said first layer of nitride semiconductor such that said first layer of nitride semiconductor forms a mesa structure.  
     
     
         23 . A method of making a semiconductor element comprising the steps of: 
 (a) epitaxially growing a nitride semiconductor structure on a silicon substrate; then    (b) bonding a carrier to said nitride semiconductor structure; then    (c) removing said silicon substrate from said nitride semiconductor structure.    
     
     
         24 . A method as claimed in  claim 23  further comprising the step of applying a base material other than silicon on said nitride semiconductor structure after removing said silicon substrate.  
     
     
         25 . A method as claimed in  claim 24  further comprising the step of removing said carrier after applying said base material.  
     
     
         26 . A method as claimed in  claim 25  further comprising the step of treating said nitride semiconductor structure before said step of bonding the carrier to form one or more devices in said structure.  
     
     
         27 . A method as claimed in  claim 25  further comprising the step of treating said nitride semiconductor structure to form one or more devices in said structure after said step of removing the carrier.  
     
     
         28 . A method as claimed in  claim 25  wherein said step of applying a base material includes depositing said base material on said nitride semiconductor structure to form a film of said base material on a bottom surface of the nitride semiconductor structure, remote from said carrier.  
     
     
         29 . A method as claimed in  claim 28  wherein said step of depositing said base material includes depositing a base material selected from the group consisting of aluminum nitride and diamond.  
     
     
         30 . A method of making a semiconductor element, said method comprising: 
 providing a nitride semiconductor structure having one or more epitaxially-grown layers atop a base supporting said nitride semiconductor structure, said base being a structure other than a substrate used in epitaxial growth of said nitride semiconductor structure, said semiconductor element not including the substrate used in epitaxial growth of said nitride semiconductor structure.    
     
     
         31 . A method as claimed in  claim 30  wherein said base is formed from a material selected from the group consisting of nitride semiconductors and diamond.  
     
     
         32 . A method of making a semiconductor structure on a silicon substrate comprising the steps of: 
 (a) depositing a layer of aluminum less than about 10 atomic monolayers thick on the top surface of the substrate to form an aluminum-protected substrate; and then    (b) depositing at least one nitride semiconductor on the aluminum-protected substrate.    
     
     
         33 . A method as claimed in  claim 32  wherein said step of depositing a nitride semiconductor includes exposing the aluminum-protected substrate to an atmosphere which includes one or more organometallic compounds and ammonia.  
     
     
         34 . A semiconductor structure made by a process as claimed in  claim 32 .  
     
     
         35 . A method of making a vertical current conduction Schottky diode comprising: 
 forming at least one layer of nitride semiconductor on a surface of a silicon substrate;    depositing at least one first metal layer on said layer of nitride semiconductor to form a Schottky contact therewith; and    depositing at least one further metal layer on another surface of said silicon substrate to form an ohmic contact therewith.    
     
     
         36 . A method as claimed in  claim 35  wherein said one layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         37 . A method as claimed in  claim 35  wherein said one layer of nitride semiconductor includes GaN.  
     
     
         38 . A method as claimed in  claim 35  further comprising forming a buffer structure on said surface of said silicon substrate prior to forming said layer of nitride semiconductor.  
     
     
         39 . A method as claimed in  claim 38  wherein said step of forming said buffer structure includes growing at least one superlattice that includes a plurality of nitride semiconductors of different compositions.  
     
     
         40 . A method as claimed in  claim 38  wherein said step of forming said buffer structure includes growing a first superlattice, growing an intermediate layer of nitride semiconductor overlying said first superlattice, and growing a second superlattice overlying said intermediate layer.  
     
     
         41 . A method as claimed in  claim 35  further comprising depositing a layer of aluminum directly on said silicon substrate.  
     
     
         42 . A method as claimed in  claim 41  further comprising forming a polycrystalline nucleation layer that includes a nitride semiconductor directly on said aluminum layer.  
     
     
         43 . A method as claimed in  claim 35  further comprising forming a further layer of nitride semiconductor prior to forming said first layer of nitride semiconductor; said further layer of nitride semiconductor having a higher doping concentration than that of said first layer of nitride semiconductor.  
     
     
         44 . A method as claimed in  claim 43  wherein said further layer of nitride semiconductor includes a gallium nitride-based semiconductor.  
     
     
         45 . A method as claimed in  claim 43  wherein said further layer of nitride semiconductor includes GaN.  
     
     
         46 . A method as claimed in  claim 35  further comprising removing a portion of said layer of gallium nitride such that said layer of gallium nitride forms a mesa structure.