The electrical transport properties of simultaneously deposited, B-doped homoepitaxial and polycrystalline diamond thin films have been evaluated by Hall-effect and resistivity measurements over a temperature range of 80–600 K. The same films were later characterized by scanning electron microscopy, secondary-ion-mass spectroscopy, and an oxidation defect etch. The study involved four sets of chemical-vapor-deposited diamond films with individual B concentrations ranging from 1.5×1017 to 1.5×1020 cm−3. In each of the four cases the mobility of the polycrystalline film was lower than that of the homoepitaxial film by 1–2 orders of magnitude over the entire temperature range. Polycrystalline films also incorporated 2–4 times more B, had 3–5 times higher compensation ratios, and displayed activation energies that were 0.05–0.09 eV lower than in the homoepitaxial films. Hopping conduction was observed in both types of films at low temperatures, but was enhanced in polycrystalline films as evident by higher transition temperatures. Preliminary efforts have been made to evaluate these results by considering the possible effects of crystal structure, compensation, impurity segregation, grain-boundary trapping, and impurity conduction.
Epitaxial growth of compound semiconductors on the (001) exhibits an asymmetry in the dislocation morphology in the two 〈110〉 directions for thicknesses near the critical thickness. The source of the asymmetry has been investigated by growth of a thickness wedge of p- and n-type GaAs0.95 P0.05 on GaAs by metalorganic chemical vapor deposition. The effect of misorientation on the resolved shear stress for each slip system has been calculated and eliminated as the source of the asymmetry. The thickness gradient was also eliminated as the source. A definitive correlation can be made between the asymmetry and the differences in the Peierls barriers of the two types of dislocations. The asymmetry results in two different critical thicknesses, one for each type of dislocation. The Peierls barriers are more similar in p-type material than in n-type material. In agreement with this, a reduced amount of asymmetry was observed in the p-type overgrowth as compared to the n-type. The nucleation barrier differences between the two types of dislocations are shown to be an unlikely source of the asymmetry.
A critical-thickness model is proposed for lattice-mismatched epitaxial layers which incorporates for the first time both the equilibrium and kinetic components of misfit accommodation. The model is an attempt to provide a physical basis for the discrepancy between the observed and calculated critical thickness in zinc-blende semiconductors. The equilibrium components of the model use a force balance and a Volterra description of the dislocation line tension with frictional forces includiing Peierls barriers and dislocation atmospheres. The effect of the frictional forces is to shift the critical thickness to a larger value and to produce a residual elastic strain which persists for large thicknesses. The frictional barriers are low in face-centered-cubic metals and produce minor changes from the previous theories; however, for semiconductors the frictional forces may be high and produce a substantial increase in the predicted critical thickness. The kinetic component of misfit accommodation has been addressed through a dynamic frictional force. The explicit form of the kinetic component of misfit accommodation depends on the operative mechanism of misfit-dislocation generation. A simple criterion is proposed to estimate whether the generation of misfit dislocations will be controlled by equilibrium or kinetic factors.
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