Investigation of the Internal Carrier Distribution in 4H-SiC Pin-Diodes by Laser Absorption Experiments

Abstract

We present an experimental equipment for studying the charge carrier distribution in the interior of bipolar 4H-SiC high power devices by means of laser absorption measurements. Since the light absorption coefficient in a semiconductor depends on the electron and hole concentration, the attenuation of a laser beam transmitted through a sample is an integral function of the local charge carrier density. In order to detect the tiny changes in the light intensity caused by the plasma-optical effect, a highly sensitive measurement set-up has been developed. Its crucial components are a low-noise blue laser and a high-speed and broad-band photo-diode amplifier circuit. Sample preparation is sophisticated and requires special care. We investigated charge carrier profiles in 4H-SiC pin-diodes in the high-injection regime at current densities between 175 A/cm² and 350 A/cm². The measured charge carrier profiles are in good agreement with computer simulations.

Carrier Concentration Analysis in 1.2 kV SiC Schottky Diodes Under Current Crowding

“…Based on carrier power absorption of a laser beam, the Free-Carrier Absorption (FCA, mainstream technique) may be used [8]- [11], but with drawbacks. In WBG vertical devices, its accuracy is limited by, not only the lack of specific calibration approaches, but also the device slicing and similar thickness of its drift region to the beam diameter [10]- [12], as they distort the actual carrier density and detected laser power [13].…”

Interpretation of laser absorption measurements on 4H-SiC bipolar diodes by numerical simulation

“…This motivated us to set up an experimental platform for the direct space-and time-resolved measurement of carrier profiles using a laser-aided probing technique, which exploits the plasma-optical effect, i.e. the sensitivity of the complex refractive index to the carrier concentrations [1]. The correct interpretation of the measured light absorption and deflection signals is quite involved and requires an accurate physical model of the measurement process itself.…”

Laser Deflection Measurements for the Determination of Temperature and Charge Carrier Distributions in 4H-SiC Power Diodes

“…Recently we reported on a laser-assisted measurement setup for determining the charge carrier distributions in the i-region of SiC bipolar diodes by laser absorption measurements [1]. Now this setup has been extended to allow for laser deflection experiments too.…”