Imaging of surface states and the interpretation of STM images from the GaAs surface

Full text: Atomic resolution STM images of semiconductor surfaces are often formed by tunneling to or from the state density of a small number of surface electronic states. Images of the GaAs(001) surface not only show a large number of possible surface geometries but also show atomic resolution features identifiable with particular bonding or nonbonding states. Unfortunately the identification these states from images is not straight forward since the effect of a localised electric field resulting from a biased tip will cause the semiconducting surface band structure to shift in energy relative to the sample Fermi level. The effect of this 'tip induced band bending, will be discussed with reference to images acquired from the GaAs(001)-(2 x 4) reconstruction. These images show that factors such as dopant levels, surface defect concentration and bias voltage all contribute to the apparent resolution of the microscope by determining which energy levels contribute to image formation