Method and apparatus for producing large, single-crystals of aluminum nitride

Abstract

A method and apparatus for producing bulk single crystals of AlN having low dislocation densities of about 10,000 cm −2 or less includes a crystal growth enclosure with Al and N 2 source material therein, capable of forming bulk crystals. The apparatus maintains the N 2 partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in the crystal growth enclosure. The Al and N 2 vapor is then deposited to grow single crystalline low dislocation density AlN at the nucleation site. High efficiency ultraviolet light emitting diodes and ultraviolet laser diodes are fabricated on low defect density AlN substrates, which are cut from the low dislocation density AlN crystals. Bulk crystals of ZnO may also be produced using the method.

1 . A method for preparing a device, wherein said device is selected from the group consisting of solid-state laser diodes and solid state light emitting diodes, said method comprising the steps of: 
 (a) evacuating a growth chamber;    (b) pressurizing said growth chamber to about 1 bar (100 kPa) with a gas including about 95% nitrogen and about 5% hydrogen;    (c) placing source polycrystalline AlN in a proximal end of a crystal growth enclosure;    (d) placing a distal end of said crystal growth enclosure in a high temperature region of said growth chamber;    (e) ramping said high temperature region to about 1800° C.;    (f) maintaining pressure in said growth chamber at about 1.3 bar (130 kPa);    (g) ramping said high temperature region to about 2200° C.;    (h) moving said distal end of said crystal growth enclosure toward a low temperature region of said growth chamber at a rate of about 0.6 to about 0.9 millimeters per hour to form a bulk single crystal of aluminum nitride at said distal end of said crystal growth enclosure;    (i) removing said bulk single crystal of aluminum nitride from said distal end of said crystal growth enclosure;    (1) cutting said removed bulk single crystal of aluminum nitride to form a substrate of aluminum nitride; and    (k) depositing at least two layers onto said substrate of aluminum nitride, wherein each layer is independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof.    
   
   
       2 . The method of  claim 1 , further comprising after step (0) and before step (k) the step of preparing a surface on said substrate of aluminum nitride to receive said at least two layers.  
   
   
       3 . The method of  claim 1 , further comprising after step (k) the steps of depositing a metal layer onto a top surface of said at least two layers and patterning said metal layer.  
   
   
       4 . A method for preparing a device, wherein said device is selected from the group consisting of solid-state laser diodes and solid state light emitting diodes, said method comprising the steps of: 
 (a) providing in a crystal growth enclosure Al and N 2  vapor;    (b) maintaining in said crystal growth enclosure, N 2  partial pressure at greater than stoichiometric pressure relative to the Al;    (c) maintaining the total vapor pressure in said crystal growth enclosure at super-atmospheric pressure;    (d) providing at least one nucleation site in said crystal growth enclosure;    (e) cooling said at least one nucleation site relative to other locations in said crystal growth enclosure;    (f) depositing said vapor under conditions capable of growing single crystalline AlN originating at said at least one nucleation site to form a bulk single crystal of aluminum nitride;    (g) removing said bulk single crystal of aluminum nitride from said crystal growth enclosure;    (h) cutting said removed bulk single crystal of aluminum nitride to form a substrate of aluminum nitride; and    (i) depositing at least two layers onto said substrate of aluminum nitride, wherein each layer is independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof.    
   
   
       5 . The method of  claim 4 , further comprising after step (h) and before step (i) the step of preparing a surface on said substrate of aluminum nitride to receive said at least two layers.  
   
   
       6 . The method of  claim 4 , further comprising after step (i) the steps of depositing a metal layer onto a top surface of said at least two layers and patterning said metal layer.  
   
   
       7 . A method for preparing a device, wherein said device is selected from the group consisting of solid-state laser diodes and solid state light emitting diodes, said method comprising the steps of: 
 (a) providing in a crystal growth enclosure Al and N 2  vapor capable of forming crystals;    (b) maintaining in said crystal growth enclosure, N 2  partial pressure at greater than stoichiometric pressure relative to the Al;    (c) providing at least one nucleation site in said crystal growth enclosure;    (d) cooling said at least one nucleation site relative to other locations in said crystal growth enclosure;    (e) generating a macroscopic flow of Al and N 2  vapor past said at least one nucleation site;    (f) depositing said vapor at said at least one nucleation site to form said bulk single AlN crystal;    (g) removing said bulk single crystal of aluminum nitride from said distal end of said crystal growth enclosure;    (h) cutting said removed bulk single crystal of aluminum nitride to form a substrate of aluminum nitride; and    (i) depositing at least two layers onto said substrate of aluminum nitride, wherein each layer is independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof.    
   
   
       8 . The method of  claim 7 , further comprising after step (h) and before step (i) the step of preparing a surface on said substrate of aluminum nitride to receive said at least two layers.  
   
   
       9 . The method of  claim 7 , further comprising after step (i) the steps of depositing a metal layer onto a top surface of said at least two layers and patterning said metal layer.  
   
   
       10 . A method for preparing a device, wherein said device is selected from the group consisting of solid-state laser diodes and solid state light emitting diodes, said method comprising the steps of: 
 (a) providing Al and N 2  vapor in a crystal growth enclosure containing a crystal growth surface;    (b) maintaining in said crystal growth enclosure, N 2  partial pressure at greater than stoichiometric pressure relative to the Al;    (c) maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure;    (d) depositing said Al and N 2  vapor on said crystal growth surface under conditions dictating the growth of a bulk, single crystal of aluminum nitride thereon;    (e) removing said bulk single crystal of aluminum nitride from said crystal growth surface;    (f) cutting said removed bulk single crystal of aluminum nitride to form a substrate of aluminum nitride; and    (g) depositing at least two layers onto said substrate of aluminum nitride, wherein each layer is independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof.    
   
   
       11 . The method of  claim 10 , further comprising after step (f) and before step (g) the step of preparing a surface on said substrate of aluminum nitride to receive said at least two layers.  
   
   
       12 . The method of  claim 10 , further comprising after step (g) the steps of depositing a metal layer onto a top surface of said at least two layers and patterning said metal layer.  
   
   
       13 . A solid-state ultraviolet (UV) laser diode comprising at least two layers, each independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof, wherein said laser diode is disposed atop a substrate of AlN having a dislocation density of about 10,000 cm −2  or less.  
   
   
       14 . The laser diode of  claim 13 , wherein said laser diode emits UV radiation at wavelengths ranging from about 200 nm to about 320 nm.  
   
   
       15 . A solid-state ultraviolet (UV) light-emitting diode comprising at least two layers each independently selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof, wherein said light emitting diode is disposed atop a substrate of AlN having a dislocation density of about 10,000 cm −2  or less.  
   
   
       16 . The light emitting diode of  claim 15 , wherein said light emitting diode emits UV radiation at wavelengths ranging from about 200 nm and 320 nm.  
   
   
       17 . The light-emitting diode of  claim 15 , wherein the fraction of electric power converted into UV radiation power is >10%.  
   
   
       18 . A method of producing bulk single-crystal ZnO, said method comprising the steps of: 
 (a) providing Zn and O 2  vapor in a crystal growth enclosure;    (b) maintaining in said crystal growth enclosure, O 2  partial pressure at greater than stoichiometric pressure relative to the Zn partial pressure;    (c) providing at least one nucleation site in said crystal growth enclosure;    (d) cooling said at least one nucleation site relative to other locations in said crystal growth enclosure; and    (e) depositing said vapor under conditions capable of growing single crystalline ZnO originating at said at least one nucleation site.    
   
   
       19 . The method of  claim 18 , wherein said cooling step (d) comprises disposing said crystal growth enclosure within a temperature gradient.  
   
   
       20 . The method of  claim 19 , further comprising moving said crystal growth enclosure through said temperature gradient during said depositing step (e).