An apparatus and method of forming a composite body including the steps of forming a diamond material layer having a first surface from diamond crystals having a nitrogen content of less than 100 ppm; providing a substrate; and bonding the first surface of the diamond material layer and the substrate under high pressure and high temperature. The composite body has a diamond material layer formed from diamond crystals having a nitrogen content of less than 100 ppm. The diamond material layer has a first surface and a substrate. The first surface of the diamond material layer and the substrate are bonded together under high pressure and high temperature.