Scanning Tunneling Microscopy for Morphological Characterization of InN Thin Films

InN is a promising semiconductor material because of its wide energy band gap (~ 2 eV). This characteristic makes the material, in concert with analogous group III metal nitrides, suitable for the production of electromagnetic sources and detectors tuned to cover the visible part of the optical spectrum. In order to make the appropriate electronic devices thin films of InN of good quality material have to be produced. This is so far the issue preventing the utilization of this material for device applications. Several techniques of film deposition have been and continue to be investigated in order to obtain device quality material. Among them, reactive magnetron sputtering offers to be a promising deposition technique. Crystalline films produced by reactive magnetron sputtering and other deposition techniques exhibit columnar microstructure. The structure consists of a network of low density material or voids that surrounds an array of parallel rod-shaped columnar regions of higher density. The formation of those columns are known to depend on the deposition parameters. Among them are the nature of the substrate [1], the rate of deposition [2], the pressure and composition of the gas phase [3], the film thickness and the ratio between the substrate temperature Ts and the film material melting point Tm [4,5]. The presence of microscopic voids within the grains contributes to the degradation of the surface flatness and to the formation of surface porosity [6].