areas. The former component can be described with the formula , whereat represents the sheet resistance of the semiconductor substrate and the width of the metal pads. The other component that contributes to the total resistance is denoted by because when two adjacent pads are characterized two identical metallized areas have to be considered. This means that the rotal resistance can be written in the following functional form, with the pad distance as independent variable: If the contribution of the metal layer itself is neglected then arises because of the voltage drop at the metal-semiconductor interface as well as in the semiconductor substrate underneath. This means that during a total resistance measurement, the voltage drops exponentially (and hence also the current density) in the metallic regions (see also theory section for further explanation). As it is derived in the next section of this article the majority of the voltage drop underneath a metallic pad takes place within in the length which is defined as the transfer length . Metaphorically speaking this means that the main part of the area underneath a metallic contact through which current enters the metal via the metal-semiconductor interface is given by the transfer length multiplied with the width of the pad . This situation is also depicted in the figure in this section where the current density distribution underneath two adjacent metal pads during a resistance measurement is depicted with a green colouring. All in all this means that (if the metal pad length is much larger than the transfer length) that a relation between and can be stated: Since can be extracted from a linear fit through the data points and can be obtained from the y-intercept of the linear fit an estimation of is possible. Circular TLM The original TLM method as described above has the drawback, that the current does not just flow within the area given by times . This means that the current density distribution also spreads to the vertical sides of the metallic pads in the figure in the TLM section, a phenomenon that is not considered in the derivation of the formula describing . To account for this geometrical issue instead of rectangular metallic pads, circular pads with radius are used which are separated from a holohedral metallic coating by a distance (see figure to the right). When the total resistance between circular pad and holohedral coating is