Influence of surface processing and passivation on carrier concentrations and transport properties in AlGaN/GaN heterostructures

Abstract

The influence of surface chemical treatments and of deposition of a SiO 2 surface passivation layer on carrier distributions and mobility in Al x Ga 1Ϫx N/GaN heterostructure field-effect-transistor epitaxial layer structures is investigated. Surface chemical treatments are found to exert little influence on carrier distribution and mobility. Deposition of a SiO 2 surface passivation layer is found to induce an increase in electron concentration in the transistor channel and a decrease in mobility. These changes are largely reversed upon removal of the SiO 2 layer by wet etching. These observations are quantitatively consistent with a shift in Fermi level at the Al x Ga 1Ϫx N surface of approximately 1 eV upon deposition of SiO 2 , indicating that the Al x Ga 1Ϫx N/SiO 2 interface has a different, and possibly much lower, density of electronic states compared to the Al x Ga 1Ϫx N free surface.

Influence of passivation induced stress on the performance of AlGaN/GaN HEMTs

“…It has been demonstrated that silicon nitride can be used as the material for a passivation to reduce the current collapse and microwave power degradation in intentionally undoped AlGaN/GaN HEMTs [2]. Consequently, many controversial results were published on passivated AlGaN/GaN HEMTs [3,4]. On the other hand, it is known from Si-electronics that the properties of passivation layers strongly depend both on the process of deposition and on the type of passivation layer [5].…”

Enhancement in electrical properties of GaN heterostructure field‐effect transistor by Si atom deposition on AlGaN barrier surface

“…The electrical properties of 2DEG can be closely related to the surface properties of the GaN HFETs via polarization effects [11,12]. On the baisis of a simple electrostatic analysis, it is speculated that a change in the surface potential of GaN HFETs can lead to a change in the 2DEG density [13]. The surface potential distribution of GaN HFETs with selective-area deposition of Si atoms was investigated by Kelvin probe force microscopy (KFM).…”

XPS study of surface potential in AlGaN/GaN heterostructure with Cat‐CVD SiN passivation

“…Surface properties of AlGaN/GaN heterostructures are closely connected to the 2DEG density via polarization effects [7,8]. Dang et al have speculated, on the basis of a simple electrostatic analysis, that surface passivation on AlGaN/GaN heterostructures can change AlGaN surface potential, thereby leading to a modulation in the 2DEG density [9]. In this study, we directly measure AlGaN surface potentials in AlGaN/GaN heterostructures with and without Cat-CVD SiN passivation using x-ray photoelectron spectroscopy (XPS), and experimentally demonstrate that a reduction in the AlGaN surface potential is actually induced by Cat-CVD SiN passivation, which is likely to be a significant cause of increase in the 2DEG density.…”