Measurement technique offers advances in semiconductor technology

In Applied Physics Letters, investigators in Japan and Sweden report a method for determining doping concentrations in p-type silicon carbide (SiC) semiconductors using photoluminescence (PL) measurements. The investigators observed a linear relationship between the concentration of aluminum (Al) in the doped semiconductors and the ratio of PL intensities of Al-bound and free-exciton emissions. This linear relationship can, thus, be used as a calibration curve to determine Al doping concentrations in samples.

While previous studies employed this technique, the researchers were able to extend the range of Al concentrations that can be measured to over three orders of magnitude by varying the temperature. A similar approach has been used for other dopants, but this report represents the first time the method has been successfully implemented for p-type SiC semiconductors, according to the lead investigator, Satoshi Asada. Asada added that previous attempts to measure dopant concentrations in these systems were impeded by the unintentional incorporation of nitrogen.

Asada said the method described in this paper represents an important advance because it allows for non-destructive characterization of the semiconductor. In addition, the method enables precise measurements of small portions of a SiC wafer and can, thus, reveal local inhomogeneities. This is useful for device fabrication and quality control but should also help investigators understand how dopants are distributed during the growth process.

Device characteristics such as breakdown voltage, on-resistance, transfer conductance and current gain all depend on doping concentration, so the ability to measure and control this critical parameter would have a direct bearing on future device development. According to Asada, the research group envisions extending their method to simultaneous measurement of n- and p-type dopants in semiconductors.

Source: “Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC,” by Satoshi Asada, Tsunenobu Komoto, and Ivan G. Ivanov, Applied Physics Letters (2017). The article can be assessed at https://doi.org/10.1063/1.4989648 .