Characterization of Light Emission from 4H and 6H SiC MOSFETs

Abstract

While SiC devices are an attractive alternative to Si in high power applications, interface trap densities measured in SiC-based MOSFETs are significantly larger than in Si-based ones. Here, we study SiC MOSFETs using both spatial images and spectral analysis of light emission due to electron-hole recombination. The light emission is produced by alternately driving the channel between accumulation and inversion using what is essentially a charge-pumping set-up. Emission is due to interface trap and bulk electron-hole recombination. The spatial imaging studies suggest that recombination occurs at both interface traps and bulk defects. Spectral studies of the emission indicate the presence of a narrow band centered at 425 nm and a broad band extending from approximately 500 to 800nm. The former we suggest is due to bulk recombination and the latter to interface trap recombination. The spectral studies of the 500 to 800 nm band are timed to separate light emitted during the inversion-to-accumulation transition from that emitted during the accumulation-to-inversion transition and visa versa. Comparisons of the emission spectra collected during these specific periods are consistent with a larger Dit in the upper half of the bandgap than the lower half in both 4H and 6H devices.

Electrically stimulated optical spectroscopy of interface defects in wide-bandgap field-effect transistors

“…Emission microscopy. First, we employed emission microscopy to visualize the photon emission created during continuous gate switching as observed by Stahlbush et al 37,38 and Macfarlane et al 39 . However, in contrast to their work, we inspected the devices from the reverse side (see Fig.…”

“…4 a). By continuously switching the gate voltage of the MOSFET, light emission is detected both at the rising and the falling edge of the gate signal, hinting towards two different types of recombination 39 . Temporally integrating a single SiPM peak yields the released photo charge at the respective gate voltage transient, which is proportional to the number of impinged photons (see Fig.…”

“… Previous studies 37 – 39 detected through the polysilicon gate contact (left). Not only did this require dedicated test structures, but the absorption of intermediate layers and interfaces also disturbed the extraction of the created photons.…”

“…Others have also performed optical experiments based on laser excitation [30][31][32][33][34][35][36] . In contrast to these well-known approaches, there have been only a few indications that switching a SiC MOSFET electrically from accumulation to inversion or vice versa can lead to light emission via a radiative recombination process [37][38][39][40] . By detecting photons through the polysilicon and the SiO 2 gate dielectric of dedicated test structures, field-effect stimulated radiative recombination was observed in the SiC bulk and via defects at the SiC/SiO 2 interface, whereby the focus was mainly on time-gating the spectral detection and spatially resolving the spread of the recombining charges.…”

Electroluminescence Spectra of a Gate Switched MOSFET at Cryogenic and Room Temperatures Agree with Ab Initio Calculations of 4H-SiC/SiO₂-Interface Defects

“…When the atomic defect configurations of interface traps are known, the development of defect density reducing techniques is facilitated. Here, we use energy-resolved electroluminescence measurements [3,4,5,6] at cryogenic temperatures in combination with ab initio calculations to characterize the SiC/SiO 2 -interface. During the measurement the gate is switched between accumulation and inversion which results in radiative carrier recombinations via mid gap defects.…”