Coulomb-limited mobility in 4H-SiC MOS inversion layer as a function of inversion-carrier average distance from MOS interface

Abstract

The Coulomb-limited mobility (μ Coulomb ) of Si-face 4H-SiC MOSFETs with nitrided gate oxide is experimentally evaluated. μ Coulomb is experimentally determined using samples with various acceptor concentrations by varying the body bias. It is found that the depletion-charge and surface-carrier densities in the inversion layer can be utilized to well formulate μ Coulomb . In addition, μ Coulomb is investigated as a function of the inversion-carrier average distance from the MOS interface (Z AV ), and it is established that Z AV can universally describe μ Coulomb in the inversion layer of Si-face 4H-SiC MOSFETs with nitrided gate oxide.

Body doping dependence of field-effect mobility in both n- and p-channel 4H-SiC metal-oxide-semiconductor field-effect transistors with nitrided gate oxides

“…The μ FE /μ bulk ratio for both the n-and p-channel devices highly depends on E eff rather than N D,A , indicating the ionized impurities are not a dominant scattering center in both the n-and p-channel SiC MOSFETs with the nitrided gate oxides. As for the n-channel MOSFETs, it has been already reported that the ionized impurities may not dominate channel mobility, 40) and the present study revealed that the decrease in μ FE for heavily-doped SiC MOSFETs annealed in NO is not caused by ionized-impurity scattering but linked to the high E eff for both the n-and p-channel devices. Based on the result that D it near E c is higher than that near E v , scattering from trapped carriers in the p-channel devices should be weaker than that in the n-channel devices, and this may be the major reason why the μ FE /μ bulk ratio for the n-channel devices drops more sharply than that for the p-channel devices.…”

“…The major scattering mechanisms in heavily-doped MOSFETs include ionized-impurity scattering, scattering due to high E eff including roughness scattering, 32) and Coulomb scattering from fixed charges or trapped carriers near the SiO 2 /SiC interface. 40,41) To investigate the dominant scattering mechanisms in SiC MOSFETs, we applied a positive voltage to the body electrode of the p-channel devices to increase E eff while keeping the ionized-impurity (donor) density. In a similar manner, a negative body bias was applied to the n-channel devices to increase E eff .…”

Study of Carrier Mobilities in 4H-SiC MOSFETS Using Hall Analysis

“…Therefore, for electrons, transport is limited by Coulomb and phonon scattering. From the trend of the experimental results in figure in Section 3.3 and other published results [ 23 , 26 ], electron mobility will reduce below 77 K due to increased Coulomb scattering. Above 373 K, mobility would also decrease, but due to increased phonon scattering.…”

Dipole Scattering at the Interface: The Origin of Low Mobility observed in SiC MOSFETs

“…The second cause is the low free electron mobility (µ free ) of the remaining mobile electrons in the MOS channel [8,9,[11][12][13][14][15][16]. It has been found that the high density of D it near E C can be reduced and thus the n free s can be improved [8][9][10].…”

“…Owing to its technological importance, a number of detailed experimental studies on the µ free have been undertaken using Hall effect measurements [11][12][13][14][15][16]. We note that the experimental results regarding the mobility in MOSFETs are generally parameterized bt the Effective field (E eff ) in order to investigate the mobility-limiting scattering mechanisms [20][21][22][23].…”