Analysis of strain induced carrier confinement with varying passivation thickness of the Al_0.3Ga_0.7N/GaN heterostructure with graded Al_xGa_1-xN buffer on Si (111) substrate

In this study, the authors demonstrate the strain induced piezoelectric charge effect on carrier confinement at the Al_0.3Ga_0.7N/GaN heterointerface with varying passivation (Si₃N₄) thicknesses. The graded Al_0.2Ga_0.8N/Al_0.1Ga_0.9N buffer on the Si (111) substrate grown by plasma assisted molecular beam epitaxy reduces the dislocation density of the GaN layer, which significantly improves the carrier concentration at the Al_0.3Ga_0.7N/GaN interface. The carrier confinement as well as the two-dimensional electron gas (2DEG) density with varying passivation thicknesses has been investigated through high resolution x-ray diffraction (HRXRD) followed by strain analysis and capacitance–voltage (C-V) measurements. As per the HRXRD strain analysis, the 2DEG density was predicted to increase about 5%, 7.9%, and 10% after Si₃N₄ passivation of 20, 30, and 40 nm, respectively. This enhancement in carrier density (2DEGs) was then validated by C-V characteristics for the same Si₃N₄ variation. After passivation, the induced tensile strain on the Al_0.3Ga_0.7N barrier along with surface state reduction at the interface of Si₃N₄/Al_0.3Ga_0.7N effectively improves the carrier confinement at the Al_0.3Ga_0.7N/GaN interface.