Strong carrier freezeout above 77 K in tellurium-doped buried-channel MOS transistors

Semiconductor devices are almost universally based on an assumption of full ionization of dopant impurities, a natural condition at room temperature for conventional shallow-energy-level (activation energy ∼ 0.05 eV) dopant species. At temperature T < 30 K for conventional dopants, freezeout of the equilibrium carrier density becomes severe and uncompensated dopants are in the neutral charge state. The high resistivity of such frozen-out regions might have useful applications for device structures. However, the temperature (< 30 K) required makes such applications generally impractical. Freezeout-induced high-resistivity regions at 77 K would be considerably more interesting. We demonstrate strong freezeout of a buried-channel MOS transistor at 77 K using tellurium as the channel dopant.