Cross-sectional and plan view scanning tunneling microscopy of GaAs heterostructures and surfaces.

摘要

Molecular Beam Epitaxy (MBE) is used to grow a number of device structures. While a number of techniques can be used to examine the structures grown by MBE, few of them can resolve atomic scale features. Atomic scale features are important because they can have an important effect on the way growth proceeds and on the final device properties.; One technique that does have atomic-scale resolution is scanning tunneling microscopy (STM). Plan-view STM involves looking at details of the growth surface and has already been used to study many surfaces, particularly those of Silicon. Cross-sectional STM (XSTM) involves cleaving through an epitaxial structure, and looking at the details of the layers and of the interfaces between them.; We present here the results of several plan-view STM studies of the GaAs (001) growth surface. We find that the (2 x 4) reconstruction of this surface is dimerized with rows of two dimers adjacent to rows of two missing dimers. For low-temperature grown material, we show that a good quality surface is recovered when the samples are subsequently annealed.; A study of the vicinal GaAs (001) surface is also presented. Step edges are examined in detail with STM. We show that kinks in the step-edges act independently from each other and are essentially randomly placed on the surface. From the distribution of the kinks, we calculate a kink formation energy of 2.3 kT, where k is Boltzmann's Constant and T is the growth temperature. The distribution of terrace widths is also determined from STM images. We show that there seems to be a tendency for vicinal surfaces to form terrace widths of 40 A with large terraces forming in order to preserve the miscut angle.; XSTM is used to examine the growth of InGaAs islands on the GaAs (001) surface. Using this technique we can determine island shapes after the GaAs overgrowth. For a typical island we find a dot height of about 13 nm and a dot width of about 35 nm. We estimate the thickness of the wetting layer as 3 nm.