Thermally assisted tunnelling in certain GaAs heterostructures

Theoretical calculations of thermally assisted tunnelling currents enable the ideality factor η to be computed for metal/semiconductor diodes and semiconductor heterojunctions. The calculation is based on a generalization of Bethe’s original formulation of themionic emission theory with the inclusion of a tunnelling factor. Forward current-–voltage isotherms for GaAs-based structures are computed and the values of η are compared with other calculations. The forward current characteristics of Au–nGaAs Schottky barrier diodes and n (Ga,In)As–p+GaAs heterojunctions have been measured and careful comparison is made between these and other closely related structures. The temperature variation of η for highly doped (Nd1017–1018/cm3) junctions shows quantitative variations attributable to thermally assisted tunnelling effects. Applications of this theory in investigations of practical diodes are given.