Probing the surface potential of SiO2/4H-SiC(0001) by terahertz emission spectroscopy

Abstract

Terahertz (THz) emission spectroscopy (TES) was used to evaluate the properties of interfaces between thermally grown oxides and 4H-SiC(0001) substrates. Metal–oxide–semiconductor (MOS) structures with transparent electrodes were irradiated with a femtosecond laser pulse and the emitted THz signal was measured by changing the applied gate voltage. The amplitude of the THz pulse signal is dependent on the electric field, namely, band bending near the SiO2/SiC interfaces, and thus contains information on the change in the surface potential of the SiC MOS structures. We compared the peak THz amplitude (ETHz) and gate voltage (Vg) curves taken from SiC MOS structures with different interface qualities and observed a steep ETHz–Vg curve for a high-quality SiO2/SiC interface as compared with the curve for a structure with a higher interface state density. We also compared the ETHz–Vg and capacitance–voltage characteristics of SiC MOS capacitors and investigated the mechanism of THz emission from the SiC MOS structures to validate the ability of the TES technique for characterizing SiO2/SiC interfaces.

How to use terahertz emission spectroscopy for wide bandgap semiconductor evaluation

“…As we demonstrated with Si MOS, one can use TES and LTEM for the characterization of passivation and surface conditions made of wide bandgap semiconductor MOS as well. We have applied them to the SiC-MOS and obtained useful information [22]. In multiple quantum well structures GaInN/GaN, we can characterize carrier dynamics in the wells and capping layers [24].…”

“…We have applied TES and LTEM to Si-based materials and devices and proven that one can estimate various parameters, such as surface potential, work function, impurity doping density, defects density in passivation layers, surface state density, and so on, semi-quantitatively and non-contactly by just observing the THz radiation [8][9][10][11][12][13][14][15][16][17]. In the present work, we review the TES and LTEM application to wide bandgap semiconductors [18][19][20][21][22][23][24].…”