Electronic effects of ion mobility in semiconductors: Mixed electronic-ionic behavior and device creation in Si:Li

Micrometer-sized homojunction structure can be formed by applying strong electric pulses, at ambient temperatures, to Li-doped, floating zone n-Si. Two such junctions, arranged back to back, act as a transistor, as evidenced by electron-beam-induced current and current-voltage measurements. The structures are created during a time ranging from ∼100 ms to a few seconds, depending on the size of the structure. The phenomenon is similar to what was observed earlier in CuInSe₂ and was explained there by thermally assisted electromigaration of Cu. In the case of Si doped with Li we can use secondary-ion-mass spectrometry to detect the redistribution of Li after electric-field application. Such a redistribution is needed found and corresponds to an n⁺-p-n structute with the p region extending at least ∼20 μm into the bulk of Si. Structures created in Si doped with Li in this way are stable for at least 13 months after their creation. We ascribe this to the large difference between Li diffusivity at the local temperature that is reached during structure formation (∼400°C; 10^-8 cm²/s) and at room temperature (∼10^-15 cm²/s).