Scanning spreading resistance microscopy current transport studies on doped III–V semiconductors

Two-dimensional (2D) carrier concentration profiling using scanning spreading resistance microscopy (SSRM) has been carried out on molecular beam epitaxy-grown GaAs and InP dopant calibration samples. The current transport mechanisms between the diamond-coated SSRM tip and the III–V semiconductor cleaved surface (110) was investigated as a function of semiconductor dopant concentration via current–voltage (I–V) measurement. A positive or negative tip bias was applied while scanning over each dopant concentration region (1016–1019 cm−3). The results were compared to simulated I–V curves based on thermionic emission theory. The best fits to the data obtained under forward bias indicated that the contact barrier heights, φb, were much lower than expected from conventional large area planar contacts to GaAs or InP. The effect increases with increasing doping concentration, as a result of a combination of barrier height lowering mechanisms such as image forces, thermionic field emission and minority carrier in...