Methods of fabricating gallium nitride semiconductor layers by lateral overgrowth through offset masks

Abstract

Abstract of Disclosure A gallium nitride semiconductor layer is fabricated by masking an underlying gallium nitride layer with a first mask that includes a first array of openings therein and growing the underlying gallium nitride layer through the first array of openings and onto the first mask, to thereby form a first overgrown gallium nitride semiconductor layer. The first overgrown layer is then masked with the second mask that includes a second array of openings therein. The second array of openings is laterally offset from the first array of openings. The first overgrown gallium nitride layer is then grown through the second array of openings and onto the second mask, to thereby form a second overgrown gallium nitride semiconductor layer. Microelectronic devices may then be formed in the second overgrown gallium nitride semiconductor layer.

Claims 
     
         1.  A method of fabricating a gallium nitride semiconductor layer comprising the steps of: 
       masking an underlying gallium nitride layer with a first mask that includes a first array of openings therein; 
       growing the underlying gallium nitride layer through the first array of openings and onto the mask to thereby form a first overgrown gallium nitride semiconductor layer; 
       masking the first overgrown gallium nitride layer with a second mask that includes a second array of openings therein, the second array of openings being laterally offset from the first array of openings; and 
       growing the first overgrown gallium nitride layer through the second array of openings and onto the second mask, to thereby form a second overgrown gallium nitride semiconductor layer. 
     
     
         2.  A method according to  Claim 1  wherein the step of growing the first overgrown gallium nitride layer is followed by the step of forming at least one microelectronic device in the second overgrown gallium nitride semiconductor layer. 
     
     
         3.  A method according to  Claim 1  wherein the step of growing the first overgrown gallium nitride layer comprises the step of growing the first overgrown gallium nitride layer through the second array of openings and onto the second mask until the second overgrown gallium nitride layer coalesces on the second mask to form a continuous overgrown monocrystalline gallium nitride semiconductor layer. 
     
     
         4.  A method according to  Claim 1  wherein the growing steps comprise the steps of growing the underlying gallium nitride layer and growing the first overgrown gallium nitride layer using metalorganic vapor phase epitaxy. 
     
     
         5.  A method according to  Claim 1  wherein the first masking step is preceded by the step of forming the underlying gallium nitride layer on a substrate. 
     
     
         6.  A method according to  Claim 5  wherein the forming step comprises the steps of: 
       forming a buffer layer on a substrate; and 
       forming the underlying gallium nitride layer on the buffer layer opposite the substrate. 
     
     
         7.  A method according to  Claim 1  wherein the first and second masking steps comprise the steps of:masking the underlying gallium nitride layer and the first overgrown gallium nitride layer with a first mask and a second mask respectively, that include respective first and second arrays of stripe openings therein, the stripe openings extending along a 
       〈     1        1   _        00     〉                 
direction of the underlying gallium nitride layer. 
     
     
         8.  A method according to  Claim 1  wherein the underlying gallium nitride layer includes a predetermined defect density, and wherein the step of growing the underlying gallium nitride layer through the first array of openings and onto the mask to thereby form a first overgrown gallium nitride semiconductor layer comprises the steps of: 
       vertically growing the underlying gallium nitride layer through the first array of openings while propagating the predetermined defect density; and  
       laterally growing the underlying gallium nitride layer from the first array of openings onto the first mask to thereby form a first overgrown gallium nitride semiconductor layer of lower defect density than the predetermined defect density. 
     
     
         9.  A method according to  Claim 8  wherein the step of growing the first overgrown gallium nitride layer comprises the steps of: 
       vertically growing the first overgrown gallium nitride semiconductor layer through the second array of openings; and 
       laterally growing the first overgrown gallium nitride semiconductor layer from the second array of openings onto the second mask, to thereby form a second overgrown gallium nitride semiconductor layer of lower defect density than the predetermined defect density. 
     
     
         10.  A method according to  Claim 1  wherein the underlying gallium nitride layer includes a predetermined defect density, and wherein the second overgrown gallium nitride semiconductor layer is of lower defect density than the predetermined defect density. 
     
     
         11.  A method according to  Claim 1  wherein the growing steps comprise the steps of growing the underlying gallium nitride layer and growing the first overgrown gallium nitride layer using metalorganic vapor phase epitaxy of triethylgallium at 13-39µmol/min and ammonia at 1500 sccm at a temperature of 1000ºC-1100ºC. 
     
     
         12.  A method according to  Claim 7  wherein the steps of growing the underlying gallium nitride layer and growing the first overgrown gallium nitride layer comprise the steps of growing the underlying gallium nitride layer and the first overgrown gallium nitride layer using metalorganic vapor phase epitaxy of triethylgallium at 26µmol/min and ammonia at 1500 sccm at a temperature of 1100ºC. 
     
     
         13.  A method of fabricating a gallium nitride semiconductor layer comprising the steps of: 
       laterally growing an underlying gallium nitride layer to thereby form a first laterally grown gallium nitride semiconductor layer; and 
       laterally growing the first laterally grown gallium nitride layer, to thereby form a second laterally grown gallium nitride semiconductor layer. 
     
     
         14.  A method according to  Claim 13  wherein the step of laterally growing the first laterally grown galliumm nitride layer is followed by the step of forming at least one microelectronic device in the second laterally grown gallium nitride semiconductor layer. 
     
     
         15.  A method according to  Claim 13  wherein the step of laterally growing the first laterally grown gallium nitride layer comprises the step of laterally growing the first laterally grown gallium nitride layer until the second laterally grown gallium nitride layer coalesces to form a continuous laterally grown monocrystalline gallium nitride semiconductor layer. 
     
     
         16.  A method according to  Claim 13  wherein the laterally growing steps comprise the steps of laterally growing the underlying gallium nitride layer and laterally growing the first laterally grown gallium nitride layer using metalorganic vapor phase epitaxy. 
     
     
         17.  A method according to  Claim 13  wherein the step of laterally growing the first laterally grown gallium nitrde layer comprises the step of laterally overgrowing the first laterally grown gallium nitride layer. 
     
     
         18.  A method according to  Claim 13  wherein the underlying gallium nitride layer includes a predetermined defect density, and wherein the step of laterally growing the first laterally grown gallium nitride layer comprises the step of: 
       laterally growing the first laterally grown gallium nitride semiconductor layer, to thereby form a second laterally grown gallium nitride semiconductor layer of lower defect density than the predetermined defect density. 
     
     
         19.  A method according to  Claim 2  wherein the step of forming at least one microelectronic device in the second overgrown gallium nitride semiconductor layer comprises the step of forming at least one microelectronic device in the second overgrown gallium nitride semiconductor layer and in the first overgrown gallium nitride layer. 
     
     
         20.  A method according to  Claim 14  wherein the step of forming at least one microelectronic device in the second laterally grown gallium nitride semiconductor layer comprises the step of forming at least one microelectronic device in the second laterally grown gallium nitride semiconductor layer and in the first laterally grown gallium nitride semiconductor layer. 
     
     
         21.  A method according to  Claim 1  wherein the first and second arrays of openings extend along a 
       〈     11        2   _        0     〉                 
direction of the underlying gallium nitride layer. 
     
     
         22.  A method according to  Claim 1  wherein the first and second arrays of openings extend along a 
       〈     11        2   _        0     〉                 
direction of the underlying gallium nitride layer, the first mask and the second mask also including respective third and fourth arrays of openings therein that extend along a 
       〈     1        1   _        00     〉                 
direction of the underlying gallium nitride layer. 
     
     
         23.  A method according to  Claim 22  wherein the first and third arrays of openings and the second and fourth arrays of openings are arranged in rectangles on the underlying gallium nitride layer and on the first overgrown gallium nitride semiconductor layer, respectively, the openings having edges of predetermined lengths, and wherein a ratio of the predetermined lengths is proportional to a ratio of growth rates of a 
       {     11        2   _        0     }                 
 facet and a 
       {     1        1   _        01     }                 
facet of the underlying gallium nitride layer. 
     
     
         24.  A method according to  Claim 13  wherein the first laterally grown gallium nitride semiconductor layer includes spaced apart stripes that extend along a 
       〈     1        1   _        00     〉                 
direction of the underlying gallium nitride layer. 
     
     
         25.  A method according to  Claim 13  wherein the first laterally grown gallium nitride semiconductor layer includes spaced apart stripes that extend along a 
       〈     11        2   _        0     〉                 
direction of the underlying gallium nitride layer. 
     
     
         26.  A method according to  Claim 13  wherein the first laterally grown gallium nitride semiconductor layer includes an array of first spaced apart regions that extend along a 
       〈     11        2   _        0     〉                 
direction of the underlying gallium nitride layer, and an array of second spaced apart regions that extend along a 
       〈     1        1   _        00     〉                 
direction of the underlying gallium nitride layer. 
     
     
         27.  A method according to  Claim 26  wherein the array of first spaced apart regions and the array of second spaced apart regions are arranged in a rectangle in the first laterally grown gallium nitride semiconductor layer, the rectangle having edges of predetermined lengths, and wherein a ratio of the of the predetermined lengths is proportional to a ratio of growth rates of a 
       {     11        2   _        0     }                 
facet and a 
       {     1        1   _        01     }                 
 facet of the first laterally grown gallium nitride semiconductor layer.