Patent ID: 8585822

Claim:
A method of testing a first set of group III-nitride substrates cut from an ingot formed using a seed material, said method comprising a) selecting substrates from the first set of substrates to form a second set of substrates, the second set of substrates being a subset of the first set and therefore being a selection of substrates from the first set of substrates that does not include all members from the first set of substrates, the second set of substrates having at least one substrate selected from the substrates cut from a portion of the ingot located on one side of a seed used to form the ingot, and the second set of substrates having at least one substrate selected from the substrates cut from a second portion of the ingot located on the other side of the seed, b) analyzing samples taken from the substrates of the second set to assess values of a first property of each of the substrates of the second set, c) determining a correlation for the values of the first property, said correlation being a function of distance of each of said substrates of the second set from the seed used to form the ingot, and either i) applying said correlation to substrates not in said second set of substrates to provide estimated values of said first property for said substrates; or ii) comparing said correlation against a value of said property for the seed material to assess whether said value of the property for the seed material can be used as an estimate of the property for wafers cut from the ingot, and providing said value of the property for the seed material as the value of the property for said wafers.