Mechanism of AlGaN/GaN heterostructure field-effect transistor threshold voltage shift by illumination

It is found that AlGaN/GaN heterostructure field-effect transistor (HFET) drain current increases under illumination at a photon energy of 2.92 eV, lower than the bandgap energy. Analysis with Shockley-Read-Hall (SRH) statistics for deep traps indicates that the electron generation from deep traps in the buffer layer is responsible for the shift. The trap energy is identified that from the conduction band. High resistivity buffer layers compensated by deep traps, which are often required for high frequency applications, give larger threshold voltage variation.