Impurity conduction in phosphorus-doped buried-channel silicon-on-insulator field-effect transistors

TL;DR

This study explores impurity conduction mechanisms in phosphorus-doped silicon-on-insulator transistors, revealing a conductance peak and high-temperature variable-range hopping influenced by band bending and impurity band properties.

Contribution

It demonstrates the emergence of conductance peaks and high-temperature hopping in doped SOI transistors, linking these phenomena to impurity band structure and gate bias effects.

Findings

Conductance peak appears at low temperatures in doped transistors.

Variable-range hopping persists above 100 K, higher than expected.

Conductance features relate to impurity band and DOS characteristics.

Abstract

We investigate transport in phosphorus-doped buried-channel metal-oxide-semiconductor field-effect transistors at temperatures between 10 and 295 K. In a range of doping concentration between around 2.1 and 8.7 x 1017 cm-3, we find that a clear peak emerges in the conductance versus gate-voltage curves at low temperature. In addition, temperature dependence measurements reveal that the conductance obeys a variable-range-hopping law up to an unexpectedly high temperature of over 100 K. The symmetric dual-gate configuration of the silicon-on-insulator we use allows us to fully characterize the vertical-bias dependence of the conductance. Comparison to computer simulation of the phosphorus impurity band depth-profile reveals how the spatial variation of the impurity-band energy determines the hopping conduction in transistor structures. We conclude that the emergence of the conductance peak and the high-temperature variable-range hopping originate from the band bending and its change by the gate bias. Moreover, the peak structure is found to be strongly related to the density of states (DOS) of the phosphorus impurity band, suggesting the possibility of performing a novel spectroscopy for the DOS of phosphorus, the dopant of paramount importance in Si technology, through transport experiments.