Cross-sectional scanning tunneling microscopy studies of novel III-V semiconductor structures

In recent years, nanostructure technology involving III-V semiconductors have made significant progress in areas such as optoelectronics and spintronics. A number of new materials and nanostructures have been invented, most of them being of a very dilute character or extremely small. Because of these properties, their structural characterization on an atomic scale is of profound importance. One important technique for the structural characterization of these structures is so-called cross-sectional Scanning Tunneling Microscopy (XSTM). The III-V semiconductor is cleaved perpendicular to the (1 0 0) growth direction exposing the (1 1 0) surface. This procedure enables a sharp STM tip to probe the atomic scale details of a wide variety of buried structures. Here, results from three different III-V structures with significant technological interest are presented. The first is the atomic scale structure of dilute ferromagnetic semiconductor superlattices consisting of alternate layers of GaAs and GaMnAs with different compositions. By unraveling the appearance of the Mn atoms in XSTM, we are able to investigate the diffusion of Mn atoms into the GaAs spacer layers between the GaMnAs layers. The second example concerns stacked quantum dots of InAs in InP. XSTM from stacks of 2, 5 and 10 quantum dots are presented. A significant number of defects will be shown as well as information on the amount of alloying between the InAs quantum dots and the surrounding InP layers. The last example concerns free standing objects such as nanowires. A new method is presented which enables us to cleave nanowires and consequently observe the individual atoms inside the wire. Our XSTM images provide detailed information on the growth of the wires as well as on the formation of twins inside the wires.