Ballistic transport and properties of submicrometer Silicon MOSFET's from 300 to 4.2 K

The characteristics of submicrometer silicon MOSFET's have been measured from 300 to 4.2 K, and the mobility versus temperature and carrier velocity versus longitudinal field as a function of temperature have been plotted. Effective mobilities in 500-µm-square devices as high as 25 000 cm2/V . s at 4.2 K have been observed. Mobilities of this magnitude represent mean free path lengths that could lead to ballistic transport in submicrometer devices. Effective mobilities in 0.2-µm devices were only 800 cm2/V . s at 4.2 K due to high-field effects. The mobility versus effective channel length for 0.2-, 0.7-, and 1.7-µm devices operating at drain voltages of 0.1 V has been plotted, and it has been observed that the mobility is greatly reduced in short-channel devices. The mobility versus longitudinal field was studied, resulting in the observation that ballistic transport is inhibited by the high fields in devices operating at 0.1 V. Similar high-field effects should limit the effects of ballistic transport in high-mobility semiconductors such as submicrometer GaAs FET's Operating at nominal supply voltages.