Mobility degradation in a nano-MOSFET due to ballistic and high-field effects

The ballistic transport has been intensively discussed for years in the search for future devices with higher performance. The mobility is expected to be higher in a ballistic channel due to absence of scattering in a channel with reduced length below the scattering limited mean free path (mfp). However, almost all experimental observations [1-3] so far reveal degradation of mobility when the channel length is in the ballistic regime. Riyadi and Arora[4-5] have provided an excellent explanation that agrees well with the experimental results mobility degradation in channels with lengths below the long-channel mfp. The injection from ballistic contacts is highlighted that increases the effective mfp, called ballistic mfp ℓ_B=ℓ_0∞(v_inj/v_i)that is higher than the long channel mean free path ℓ_0∞ by injection velocity ratio v_inj/v_i to channel velocity v_i. The ballistic mfp is higher, yet the mobility is amazingly lower.