Substrate-Mediated Persistent Photodoping in WSe2/hBN Field-Effect Transistors Enabled by Defect States in SiO2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Photodoping significantly influences the optoelectronic properties of 2D semiconductor devices.
• The precise origin of trap states responsible for photodoping in these systems remains largely undetermined.

Purpose of the Study:

• To investigate the mechanisms of UV-induced photodoping in multilayer tungsten diselenide (WSe2) field-effect transistors (FETs).
• To identify the role of substrate and heterostructure components in persistent photodoping phenomena.

Main Methods:

• Fabrication of WSe2/hexagonal boron nitride (hBN) heterostructures on SiO2/p-Si substrates.
• Wavelength-dependent photodoping measurements under UV and visible light illumination.
• Device fabrication with and without the SiO2 layer.
• Analysis of defect states in SiO2 and first-principles calculations for hBN defects.

Main Results:

• Pronounced n-type photodoping observed under 405 nm illumination, significantly weaker under 640 nm light.
• Removal of the SiO2 layer drastically suppressed both n-type and p-type photodoping.
• Experimental data and theoretical calculations ruled out hBN defects as the primary source of observed effects.

Conclusions:

• Defect states within the SiO2 substrate act as crucial charge reservoirs, facilitating charge transfer and long-term carrier trapping.
• The substrate plays a dominant role in UV-induced photodoping and photogating in WSe2 FET devices.
• Understanding substrate defects is essential for optimizing optoelectronic responses in 2D materials.