Effects of radiation-induced interface-trapped charge and oxide-trapped charge on the inversion-layer carrier mobility in double-diffused metal-oxide-semiconductor (DMOS) power transistors are investigated. Interface-trapped charge is more effective in scattering inversion-layer carriers than oxide-trapped charge. However, the effects of oxide-trapped charge must be taken into account in order to properly describe the mobility behavior. An effective approach to detecting effects of oxide-trapped charge and separating these effects from effects of interface-trapped charge is demonstrated. Detection is based on analyzing mobility data sets which have different functional relationships between the two trapped charge components. These relationships may be linear or nonlinear. Separation of effects of oxide-trapped charge and interface-trapped charge is possible only if these two trapped charge components are not linearly dependent. A significant contribution of oxide-trapped charge to mobility degradation is demonstrated and quantified. Effects of oxide-trapped charge may be dominant in non-hardened DMOS transistors irradiated at relatively high dose rates. In addition, DMOS devices have been irradiated at room temperature and mobility measurements performed at room temperature and at 77 K to analyze mobility degradation due to the same density of radiation-induced defects at these two different temperatures. Radiation-induced mobility degradation is more pronounced at 77 K than at room temperature, due to increased relative importance of Coulomb scattering from trapped charge when phonon scattering is significantly reduced. Effects of oxide-trapped charge on mobility are more pronounced at cryogenic temperatures than at room temperature.
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