Paper TF+NM-MoE3
Effective Mass of a Two-Dimensional √3x√3 Ga Single Atomic Layer on Si(111)

Monday, December 8, 2014, 6:20 pm, Room Lehua

The transport of charge carriers in semiconductor nanostructures is particularly important for nanoscale devices. In a semi classical approach, the transport of charge carriers is to a large degree governed by the effective masses of electrons and holes, which are reasonably well known for most bulk materials. However, with ongoing miniaturization of semiconductor devices and the trend towards the use of nanostructures, the increasing surface to volume ratio reduces the relative fraction of bulk material. Hence, transport in semiconductor nanostructures is to a large degree determined by surface and/or interface effects, where little is known about the effective masses.

The effective masses of surface states can be derived from angle-resolved photoemission spectroscopy (ARPES), but it is hardly applicable on individual nanostructures. In contrast scanning tunneling spectroscopy (STS) is ideally suited for probing the local density of states of an individual nanostructure, but it is a very difficult task to quantitatively measure the involved k vectors and hence the dispersion relation and the effective mass.

Therefore, we illustrate here a methodology applicable to individual semiconducting nanostructures for extracting effective masses of a two dimensional √3x√3 Ga single atomic layer on Si(111) directly from scanning tunneling spectra. The methodology is based on calculating the tunnel current using its dependence on the effective density of states mass and a parabolic band approximation followed by fitting to the measured tunneling spectra. An effective mass of m_eff,C=0.59 ± 0.06 is obtained for the empty surface state, in good agreement with a band structure calculation and inverse photo electron spectroscopy data.