Methods for producing improved crystallinity group III-nitride crystals from initial group III-nitride seed by ammonothermal growth
The present invention discloses methods to create higher quality group III-nitride wafers that then generate improvements in the crystalline properties of ingots produced by ammonothermal growth from an initial defective seed. By obtaining future seeds from carefully chosen regions of an ingot produced on a bowed seed crystal, future ingot crystalline properties can be improved. Specifically, the future seeds are optimized if chosen from an area of relieved stress on a cracked ingot or from a carefully chosen N-polar compressed area. When the seeds are sliced out, miscut of 3-10° helps to improve structural quality of successive growth. Additionally a method is proposed to improve crystal quality by using the ammonothermal method to produce a series of ingots, each using a specifically oriented seed from the previous ingot. When employed, these methods enhance the quality of Group III nitride wafers and thus improve the efficiency of any subsequent device.
1. A method for growing group III nitride crystals, comprising:
(a) growing a first group III nitride ingot on a first seed crystal by an ammonothermal method until a radius of curvature of a c-plane lattice of the group III nitride ingot becomes larger than a radius of curvature of a c-plane lattice of the first seed crystal and until bowing of the c-plane lattice of the first group III nitride ingot along a slicing direction is inverted from a bowing direction of the first seed crystal along the c-plane lattice of the first seed crystal;
(b) slicing one or more wafers out of the first ingot along the slicing direction and from a nitrogen polar side of the ingot;
(c) using the one or more wafers taken from the nitrogen-polar side of the first ingot as a second seed crystal for subsequent growth of one or more second ingots by the ammonothermal method.
2. The method of claim 1 , wherein the group III nitride is GaN.
3. The method of claim 1 , wherein the bowing of the c-plane lattice along the slicing direction is improved from the bowing of the c-plane lattice of the first seed crystal.
4. The method of claim 1 , wherein strain in the second seed crystal is reduced from strain in the first seed crystal.
5. The method of claim 1 , wherein crystallinity of the second seed crystal is improved from crystallinity of the first seed crystal.
6. The method of claim 1 , wherein the one or more wafers sliced from the first group III nitride ingot are misoriented from a c-plane of the first ingot by 3 to 15 degrees.
7. The method of claim 6 , wherein the bowing of crystallographic lattice in the second seed crystal along the slicing direction is improved from the bowing of the first seed crystal.
8. The method of claim 6 , wherein strain in the second seed crystal is reduced from strain in the first seed crystal.
9. The method of claim 6 , wherein crystallinity of the second seed crystal is improved from crystallinity of the first seed crystal.