Electronic Processes and Excess Currents in Gold-Doped Narrow Silicon Junctions

Large amounts of excess current in gold-doped silicon tunnel junctions are observed and interpreted as due to transition processes with the two gold energy levels in the forbidden gap of silicon as intermediate states. Eight of the ten possible processes are two-step processes. These two steps may be both of the Hall-Shockley-Read type or of the type involving electron tunneling between a trap state and a band state within the space charge region of the junction. The two steps may also consist of a Hall-Shockley-Read process as one step, and the tunneling from or to the trap state as the other step. One of the remaining two possible processes is a three-step process involving two Hall-Shockley-Read steps and one tunneling step between two trap states within the space-charge region. The last process is the usual carrier injection process. Eight of the ten processes in the gold-doped tunnel diodes have appreciable transition rates. Five of the eight processes have onset structures which appear at voltages in reasonable agreement with the predicted values. Approximate theoretical current-voltage expressions are compared with experimental data of the gold-induced excess current at 4.2°K, giving an average value of $\frac{W^2{m}_{\perp }}{m}=1.2\mathrm{}\times {10}^{-23\mathrm{}}$ ${\mathrm{volt}}^2$-${\mathrm{cm}}^3$, where $W$ is Price's matrix element of the trap potential energy in excess of the crystal potential taken between the unnormalized trap-state wave function and the band edge Bloch wave function, normalized to unit volume, and $\frac{m_{\perp }}{m}$ is the transverse electron mass normalized to the free electron mass. It is also experimentally determined that the rate of tunneling from or to trap state is smaller than the rate of filling or emptying the trap in the Hall-Shockley-Read process.