THEORY OF TUNNELLING PROCESSES IN GERMANIUM TUNNEL DIODES. I. IMPURITY-INDUCED CURRENT; II. PHONON-ASSISTED CURRENT,

Part I deals with a theoretical analysis of the tunnelling current in germanium caused by impurity scattering. It is shown that for a high doping level approximately 10 to the 19th powercu cm the impurity-induced tunnelling current is important, being comparable with or even stronger than the phonon-assisted tunnelling current. Different impurities act differently As or P induces a stronger current than Sb. It is argued that the impurity-induced tunnelling current in germanium is dominated by a second order process. An electron tunnelling from the bottom of the conduction band into the forbidden band is first scattered by the impurities into states corresponding to the 0, 0, 0 conduction band minimum, and proceeds thereon to the valence band by virtue of the junction field. A theory is proposed for such a process and a formula for the impurity-induced tunnelling current is derived. Part II deals with a theoretical analysis of the tunnelling current in Ge induced by phonon scattering. It is pointed out that this process should be primarily, a second order one an electron tunnelling into the forbidden band from the bottom of the conduction band is first scattered by phonons into the states of the 0, 0, 0 conduction band minimum, and then makes a transition to the valence band by virtue of the junction field. It is found that the major contribution to this process is made by the lattice vibrations in a certain range about 20A in thickness of the junction field. The transition probability is almost directionally independent.