ESR in layer-substrate structures: The line shape and nondestructive contactless measurements of the layer conductivity

The electron-spin resonance of spins in a substrate may be used as a tool for investigating the electrical properties of a metallic (semiconducting) layer. This is accomplished by passing a microwave field through the layer into the substrate and detecting the distortion of the ESR line shape caused by the layer. This distortion depends upon the thickness and the conductivity of the layer, both of which may be obtained if the theoretical line shape of the ESR in such a structure is known. The theoretical line shape and the intensity of the ESR in a layer-substrate system are discussed for various pairs of layers and substrates (metal-metal, semiconductor-insulator, etc.) in the case of localized spins. The structure of the electromagnetic field in the sample is dependent upon the orientation of the constant external magnetic field with respect to the surface of the sample, but magnetic losses and the line shape do not change essentially as a function of the orientation. It is shown that the A/B ratio of the ESR line may be used for measuring the layer conductivity and/or layer thickness. An experiment in which Ge layers on a ruby substrate were studied at various temperatures is described here. Experimental data of A/B ratios are presented and layer conductivities as deduced from these ratios are in good agreement with the conductivities obtained by four-contact measurements. Possible applications of the method are discussed.