Role of a nucleation layer in suppressing interfacial pitting in

In this work, we investigate the role of a low temperature nucleation layer on the interfacial properties of InAs epilayers grown on (100) semi-insulating InP substrates using a two-step metalorganic chemical vapor deposition method. Cross-sectional and plan-view transmission electron microscopy studies were carried out on InAs films of nearly equal total film thicknesses but for different thicknesses of a nucleation layer of InAs deposited at low temperature on the substrate. Our studies show that thermal etchpits are created at the interface between the InAs film, and the InP substrate for thin nucleation layer thicknesses. This is because the low temperature nucleation layer of InAs does not cover completely the surface of the InP substrate. Hence, when the temperature is raised to deposit the bulk of the InAs film, severe thermal pitting is observed at the interface. These thermal etchpits are sources of threading dislocations. To obtain high quality InAs films and suppress interfacial pitting there is an optimum thickness of the nucleation layer. Also, our studies show that there is a relationship between the density of defects in the film and the thickness of the nucleation layer. This in turn relates to the variation of the electronic properties of the InAs films. We have observed that for all nucleation layer thicknesses, the density of threading dislocations is higher close to the interface than at the free surface of the film.