Boron delta-doped diamond structures have been synthesized using microwave plasma chemical vapor deposition, and fabricated into FET and gated Hall bar devices for assessment of the electrical characteristics. A detailed study of variable temperature Hall, conductivity and field-effect mobility measurements was completed. This was supported by Schrödinger-Poisson and relaxation time calculations based upon application of Fermi's golden rule. A two carrier-type model was developed with an activation energy of ~0.2 eV between the delta layer lowest subband with mobility ~1 cm 2 /Vs and the bulk valence band with high mobility. This new understanding of the transport of holes in such boron delta-doped structures has shown that although Hall mobility as high as 900 cm 2 /Vs was measured at room temperature, this dramatically overstates the actual useful performance of the device.a Corresponding author
Impedance spectroscopy has been used to investigate conductivity within boron-doped diamond in an intrinsic/delta-doped/intrinsic (i-δ-i) multilayer structure. For a 5 nm thick delta layer, three conduction pathways are observed, which can be assigned to transport within the delta layer and to two differing conduction paths in the i-layers adjoining the delta layer. For transport in the i-layers, thermal trapping/detrapping processes can be observed, and only at the highest temperature investigated (673 K) can transport due to a single conduction process be seen. Impedance spectroscopy is an ideal nondestructive tool for investigating the electrical characteristics of complex diamond structures.
Impedance spectroscopy has been used to investigate the conductivity displayed by diamond doped with boron in an intrinsic-δ-layer-intrinsic multilayer system with differing δ-layer thicknesses. Carrier transport within 5 nm δ-layer structures is complex, being dominated by conduction in the interfacial regions between the δ-layer and the intrinsic regions, as well as conduction within the δ-layer itself. In the case of 3.2 nm thick δ-layers the situation appears improved with uncapped samples supporting only two conduction paths, one of which may be associated with transport outside of the δ-layer, the other low transport within the δ-layer complex diamond structures. Introduction of the capping layer creates a third conduction path associated with unwanted boron in the capping layer-δ-layer interface.
An investigation of the lateral wave excited on a transition layer of finite thickness is made. The layer is located between two homogeneous half-spaces of different refractive index. A line source is placed in the medium with the lower refractive index, and an exact integral representation is obtained for the scattered field. This integral representation is asymptotically evaluated for large k0 in two parameter ranges; first, when the layer is thick compared with wavelength; second, when the distance between the source and the observation point is large compared with wavelength. The results of the asymptotic analysis show that for thick layers there exists a close connection between layer continuity and lateral-wave strength.
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