Thick single crystal diamond layer method for making it and gemstones produced from the layer

Abstract

A layer of single crystal CVD diamond of high quality having a thickness greater than 2 mm. Also provided is a method of producing such a CVD diamond layer.

1 . A layer of single crystal CVD diamond of high quality having a thickness of greater than 2 mm.  
   
   
       2 . A layer of single crystal CVD diamond according to  claim 1  having a thickness of greater than 2.5 mm.  
   
   
       3 . A layer of single crystal CVD diamond according to  claim 1  having a thickness of greater than 3 mm.  
   
   
       4 . A layer of single crystal CVD diamond according to  claim 1  having one or more of the following characteristics: 
 1) a high charge collection distance at 300 K of at least 100 μm measured at an applied field of 1 V/μm;    2) a high value for the product of the average carrier mobility and lifetime μτ such that it exceeds 1.0×10 −6  cm 2 /V at 300 K.    3) an electron mobility (μ e ) measured at 300 K greater than 2400 cm 2 V −1 s −1 ;    4) a hole mobility (μh) measured at 300 K greater than 2100 cm 2 V −1 s −1 ; and    5) in the off state, a resistivity at 300 K greater than 10 12  Ωcm at an applied field of 50 V/μm.    
   
   
       5 . A layer of single crystal CVD diamond according to  claim 4  which has a charge collection distance at 300 K greater than 150 μm  
   
   
       6 . A layer of single crystal CVD diamond according to  claim 4  and having a resistivity at 300 K greater than 2×10 13  Ωcm.  
   
   
       7 . A layer of single crystal CVD diamond according to  claim 4  and having an electron mobility at 300 K greater than 3000 cm 2 V −1 s −1 .  
   
   
       8 . A layer of single crystal CVD diamond according to  claim 4  and having a hole mobility at 300 K greater than 2500 cm 2 V −1 s −1 .  
   
   
       9 . A layer of single crystal CVD diamond according to  claim 4  and having a μτ at 300 K which exceeds 1.5×10 −6  cm 2 /V.  
   
   
       10 . A layer of single crystal CVD diamond according to  claim 1  and attached, at least in part, to a substrate.  
   
   
       11 . A diamond in the form of a gemstone produced from a layer of single crystal CVD diamond according to  claim 1 .  
   
   
       12 . A CVD diamond produced in the form of a gemstone from a layer of single crystal CVD diamond according to  claim 1  and characterised by having three orthogonal dimensions greater than 2 mm, where at least one axis lies either along the <100> crystal direction or along the principle symmetry axis of the stone.  
   
   
       13 . A method of producing a layer of single crystal CVD diamond according to  claim 1  which includes the steps of providing a diamond substrate having a surface which is substantially free of crystal defects, providing a source gas, dissociating the source gas and allowing homoepitaxial diamond growth on the surface which is substantially free of crystal defects in an atmosphere which contains less than 300 parts per billion nitrogen.  
   
   
       14 . A method according to  claim 13  wherein the substrate is a low birefringence type Ia or IIb natural, or a Ib or IIa high pressure/high temperature synthetic diamond.  
   
   
       15 . A method according to  claim 13  wherein the substrate is a CVD synthesised single crystal diamond.  
   
   
       16 . A method according to  claim 13  wherein the surface on which diamond growth occurs has a density of surface etch features related to defects below 5×10 3 /mm 2 .  
   
   
       17 . A method according to  claim 13  wherein the surface on which diamond growth occurs has a density of surface etch features related to defects below 10 2 /mm 2 .  
   
   
       18 . A method according to  claim 13  wherein the surface on which the diamond growth occurs is subjected to a plasma etch to minimise surface damage of the surface prior to diamond growth.  
   
   
       19 . A method according to  claim 18  wherein the plasma etch is an in situ etch.  
   
   
       20 . A method according to  claim 18  wherein the plasma etch is an oxygen etch using an etching gas containing hydrogen and oxygen.