high it can compensate for the stress induced by the gan when cooling and the stress of the gan would be compressive in terms of thermal expansion if the thermal expansion of the composite substrates is higher than that of the gan this would prevent cracking in the gan upon cooling with the stress of the gan compressive in some embodiments sputtered or evaporated thin films of refractory metals such as molybdenum and tungsten if deposited at elevated temperatures can induce large compressive stress in silicon this process would be a natural choice in the semiconductor processing culture if the selected metals are not detrimental to the subsequent processes e g do not introduce contamination to the gan layer or to the devices that form on the silicon substrate for example reacting with the process gases the silicon substrate and gallium nitride the economics of this approach depends on the thickness of films required to achieve the desired level of beneficial compressive stress in the gallium nitride layer later grown on the silicon wafer the advantages of this method are clean processing ease of thickness control good thermal conductivity of metal films and compatibility with downstream device processing in addition to metals other material such as ceramic films deposited by a sputtered process can also be used to induce the desired stress in the silicon substrate the thickness of such sputtered ceramic films would need to be optimized since thin films with.