Thermionic emission from the 2DEG assisted by image-charge-induced barrier lowering in AlInN/AlN/GaN heterostructures.

The effect of image charges on current transport mechanisms investigated at the nanoscale in Al(1-x)In(x)N/GaN heterostructures was studied. Current-voltage (I-V) measurements were performed locally using a conductive AFM-tip as a nanoprobe and the conduction mechanism was modeled to explain the observed behavior. This model suggests that current transport is controlled by thermionic emission (TE) of the two-dimensional electron gas (2DEG) across the potential barrier at the heterointerface, where the image charges generated by the 2DEG induce a barrier lowering at the Al(1-x)In(x)N/GaN interface, enhancing electron transport. This barrier lowering depends on the 2DEG characteristics, such as 2DEG density n(2D), first subband energy E0 and the average distance x0 of the 2DEG from the interface. By fitting the experimental I-V curves with the present model the 2DEG density was evaluated. The obtained results were in very good agreement with the Hall measurements.

Nanostructures in silicon investigated by atomic force microscopy and surface photovoltage spectroscopy.

Surface photovoltage spectroscopy (SPS) and conductive atomic force microscopy (C-AFM) have been used for the characterization of nanocrystalline hydrogenated Si (nc-Si:H). This is a promising material both for silicon-based opto-electronics as well as for photovoltaic applications. Notwithstanding its interesting properties many issues regarding the material electronic and optical properties are not completely understood. The present contribution reports microscopic and spectroscopic analyses of nc-Si:H films grown for photovoltaic applications by low-energy plasma-enhanced chemical vapor deposition technique. Electronic levels associated with defect states were investigated by SPS, whereas the conduction mechanism at a microscopic level was investigated by C-AFM.

Experimental evidence of dislocation related shallow states in p-type Si.

Theory, models, and experimental phenomena provide evidence of the existence of shallow bands in silicon induced by the dislocation strain field. Nevertheless, only deep bands, likely associated with contamination at dislocations, have been detected up to now by junction spectroscopy. Here we present the first experimental result by junction spectroscopy that assesses the existence of the dislocation related shallow states. These are found to be located at 70 and 60 meV from the valence and conduction band edge, respectively.