In the article, low energy ion induced electron emission (IIEE) is investigated on Si and Ge semiconductors. Plasma interactions on semiconductors are recently used for etching and deposition processes. According to the previous studies, the IIEE strongly depends on the surface process but this research focuses on the sub-surfaces processes such as doping type, Fermi level of the material and cleanliness level. The studies from the literature show that the IIEE measurements are affected by the electron density in the conduction band of the semiconductor. They claim that more electrons near the vacuum potential result in larger IIEE. However, the IIEE theory predicts less dependence on electron density by assuming all the emitted electrons from the valance band. Thus, there should be no direct relation between the IIEE and doping density and type for semiconductors, on the contrary to metals.
In the research, they try to measure IIEE yield from clean Si and Ge by considering n-type, intrinsic type and p-type. For the accurate measurements, ultraviolet photoelectron spectroscopy (UPS) and IIEE are used by interpreting electron energy distribution curves (EEDC). The surface work function is estimated correctly with the plots. In addition, the surface Fermi level position with respect to the valance band is measured for Si and Ge. In the study, the p-type of Si is doped with Boron, the n-type is doped with Phosphorous. The contact between two types is accomplished by the deposited Al. Ge samples are first coated with TaN, then with Al followed by sputter cleaning and chemical cleaning. It is concluded that the cleaning only removes the surface contaminants and does not affect the IIEE values.
As a result, there is no considerable dependence on doping type which shows the electron energy distributions are also independent of doping. This specifies that the conduction band electrons have minor effects compared to the valance band electrons. It is also found the intrinsic Si and Ge have larger resistances with unexpectedly lower IIEE values. The researchers deduce that the bulk resistivity can cause these lower values instead of the conduction band electron density. The obtained EEDC profiles have the same shapes supporting the theory which states the electrons come from the valance band. Also, there is no connection between the position of the Fermi level and electron emission.
Reference: Urrabazo, David, and Lawrence J. Overzet. “The effects of the Fermi level on ion induced electron emission from chemically and sputter cleaned semiconductors.” Journal of Physics D: Applied Physics 48, no. 34 (2015): 345203.
Course: AME 60637