A universal law to characterize ohmic contacts of small high electron mobility transistors

Abstract

We have processed very small high electron mobility transistor (HEMT) on the two dimensional electron gas of a GaAs/GaInAs heterostructure. The contacts (down to 2 μm wide) connect channels of different lengths and widths. We measure the saturation I(V) curves and obtain the source drain voltage at saturation. Experiments demonstrate a universal linear dependence of the saturation voltage drop with the length of the channel, whatever its width. Our experimental result is understood with basic equations of the 2D channel, taking into account the contact resistivity. The universal law Usat(L) gives a nice way to measure easily and precisely the resistivity of contacts in ultrasmall devices when their width cannot be precisely known, like in narrow two dimensional electron gas.