Electronic transport at semiconductor surfaces––from point-contact transistor to micro-four-point probes

Abstract

The electrical properties of semiconductor surfaces have played a decisive role in one of the most important discoveries of the last century, transistors. In the 1940s, the concept of surface states--new electron energy levels characteristic of the surface atoms--was instrumental in the fabrication of the first point-contact transistors, and led to the successful fabrication of field-effect transistors. However, to this day, one property of semiconductor surface states remains poorly understood, both theoretically and experimentally. That is the conduction of electrons or holes directly through the surface states. Since these states are restricted to a region only a few atom layers thick at a crystal surface, any signal from them might be swamped by conduction through the underlying bulk semiconductor crystal, as well as greatly perturbed by steps and other defects at the surface. Yet recent results show that this type of conduction is measurable using new types of experimental probes, such as the multi-tip scanning tunnelling microscope and the micro-four-point probe. The resulting electronic transport properties are intriguing, and suggest that semiconductor surfaces should be considered in their own right as a new class of electronic nanomaterials because the surface states have their own characters different from the underlying bulk states. As microelectronic devices shrink even further, and surface-to-volume ratios increase, surfaces will play an increasingly important role. These new nanomaterials could be crucial in the design of electronic devices in the coming decades, and also could become a platform for studying the physics of a new family of low-dimensional electron systems on nanometre scales. Ó

Predicted energy-loss spectrum of low-dimensional plasmons in a metallic strip monolayer on a semiconductor surface

“…[1][2][3] This surface has a surface-state band named the S 1 -state band, which provides an ideal two-dimensional ͑2D͒ system of conduction electrons. 4,5 The electron density in the S 1 -state band varies among experiments, because it is significantly affected by a tiny quantity of additional Ag adatoms or other possible dopant impurities or surface states.…”

Three-dimensional telegrapher's equation and its fractional generalization

“…In transport problems one does not expect dimensions greater than three, and the question, besides some theoretical interest, is rather irrelevant from the practical point of view. This is not, however, the case for two dimensions where transport on surfaces has a great number of applications in, for example, semiconductor electronics [68], chemical physics [69], or biophysics [70], just to name a few. The extension of the formalism to include two-dimensional walks is under current investigation.…”

Manipulation and four‐probe analysis of nanowires in UHV by application of four tunneling microscope tips: a new method for the investigation of electrical transport through nanowires

“…Therefore, in the last decades there has been extensive interest in studying the intrinsic electrical transport of low-dimensional systems. 1 -7 The four-terminal method, or Kelvin method, including the four-point collinear probe method and the van der Pauw method, a classical method for measuring the electrical conductivity of macro objects, is now being developed 8 step-by-step for use on some micro-objects, for instance, to measure the anisotropy of thin films. 9 On the other hand, nanomanipulation is achievable after the invention of scanning tunneling microscopy (STM).…”