Thallium-doped silicon ionization and excitation levels by infrared absorption

Abstract

The thallium ionization level in silicon is the lone group‐III acceptor (of the classical outer s²p atomic configuration) remaining heretofore imprecisely defined. Thallium is also the only such impurity not previously defined as to its bound‐hole (inverse hydrogenic) excitation levels within the energy gap. From room‐temperature infrared absorption data the thallium level is here located at 0.255 eV above the top of the valence band in silicon. This compares with previously reported ionization values of 0.22, 0.26, and 0.30±0.03 eV, all determined by nonoptical methods. Six thallium hydrogenic bound‐hole excitation levels were identified within the energy gap.