Interface Properties Probed by Active THz Surface Emission in Graphene/SiO2/Si Heterostructures.

Graphene/semiconductor heterostructures demonstrate an improvement of traditional electronic and optoelectronic devices because of their outstanding charge transport properties inside and at the interfaces. However, very limited information has been accessed from the interfacial properties by traditional measurement. Herein, we present an active THz surface emission spectroscopy for the interface build-in potential and charge detrapping time constant evaluation from the interface of graphene on SiO2/Si (Gr/SiO2/Si). The active THz generation presents an intuitive insight into the depletion case, weak inversion case, and strong inversion case at the interface in the heterostructure. By analyzing the interface electric-field-induced optical rectification (EFIOR) in a strong inversion case, the intrinsic build-in potential is identified as -0.15 V at Gr/SiO2/Si interface. The interface depletion layer presents 44% positive THz intrinsic modulation by the reverse gate voltage and 70% negative THz intrinsic modulation by the forward gate voltage. Moreover, a time-dependent THz generation measurement has been used to deduce the charge detrapping decay time constant. The investigation will not only highlight the THz surface emission spectroscopy for the graphene-based interface analysis but also demonstrate the potential for the efficient THz intrinsic modulation as well as the enhancement of THz emission by the heterostructures.