Experimental and Numerical Analysis of Off-State Bias Induced Instabilities in Vertical GaN-on-Si Trench MOSFETs

We analyzed the threshold-voltage dynamic instabilities induced by <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>-state stress in pseudo-vertical GaN-on-Si Trench <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small>s (TMOS). Extensive measurements revealed that <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>-state stress experiments induce a progressive increase of threshold voltage (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_T</i>), that is fully recoverable only after high-temperature cycles, so that it can appear as permanent degradation at room temperature. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_T</i> increase is found to be strongly affected by drain bias and negligibly influenced by gate bias (below threshold). Activation energy (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_A</i>) extracted from high-temperature <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_T</i> recovery experiments was determined to be ≈1 eV. We further characterized pseudo-vertical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p–n</i> junction diodes fabricated onto the same wafer as the TMOS's by means of capacitance isothermal spectroscopy. This experiment revealed depletion capacitance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DEP</sub>) instabilities with the same <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_A</i> as that characterizing the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_T</i> instability, leading to the conclusion that trap states present in the epitaxy are the cause of both observations. Numerical device simulations guided the physical interpretation of the observed phenomena, i.e., donor traps at 1 eV from the conduction band and localized in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-</i>layer lead to both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_T</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DEP</sub> instabilities in the TMOS and in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p–n</i> diode, respectively, by dynamically modulating the effective <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>-type doping density in the former and the effective depletion layer width in the latter.