III-V compound semiconductor dopant profiling using scanning spreading resistance microscopy

With the rapid growth of the optoelectronics industry, a new generation of analytical tools is required to satisfy the need for a fast and quantitative method for two-dimensional carrier concentration profiling with nanometer resolution on III-V compound semiconductors. A modified atomic force microscopy technique known as Scanning Spreading Resistance Microscopy (SSRM) has the potential to satisfy these requirements.; This work examines the usefulness of the SSRM techniques for application towards III-V optoelectronic devices. Measurements have been carried out on MBE-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 a wide range of dopant concentrations spanning 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, &phis;_B, were much lower than expected from conventional large area planar contacts to GaAs or InP. Barrier height lowering mechanisms due to image forces, thermionic field emission, and minority carrier injection are hypothesized to be responsible for the low barrier height values and their dependence on doping concentration. Under reverse bias, the theory better fits the results obtained for n-type InP and p-type GaAs compared to the larger barrier systems p-type InP and n-type GaAs, where the recombination-generation of carriers play an important role in the overall current.; It will be shown that only with the aid of staircase calibration structures based on a secondary calibration standard such as SIMS is it possible to use SSRM as a semi-reliable tool for two-dimensional dopant profiling of III-V compound semiconductors.