Simultaneous Charge Carrier Density Mapping of SiC Epilayers and Substrates with Terahertz Time-Domain Spectroscopy

TL;DR

This paper demonstrates a contactless, wide-range method using terahertz time-domain spectroscopy to map charge carrier densities in SiC wafers, enabling inhomogeneity detection and providing insights into doping levels.

Contribution

It introduces a simultaneous, non-destructive technique for mapping charge carrier densities in SiC epilayers and substrates over a broad range, with theoretical validation.

Findings

Effective wide-range carrier density measurement (8x10^15 to 4x10^18 cm^-3).

Detection of inhomogeneities across entire wafers.

Theoretical confirmation of measurement capabilities and doping range insights.

Abstract

With the growing demand for efficient power electronics, SiC-based devices are progressively becoming more relevant. In contrast to established methods such as the mercury capacitance-voltage technique, terahertz spectroscopy promises a contactless characterization. In this work, we simultaneously determine the charge carrier density of SiC epilayers and their substrates in a single measurement over a wide range of about 8x10^(15)$ cm^(-3) to 4x10^(18) cm^(-3) using time-domain spectroscopy in a reflection geometry. Furthermore, inhomogeneities in the samples are detected by mapping the determined charge carrier densities over the whole wafer. Additional theoretical calculations confirm these results and provide thickness-dependent information on the doping range of 4H-SiC, in which terahertz time-domain spectroscopy is capable of determining the charge carrier density.