Microwave Spectroscopy of Resistive Film Gated Higfets and Mosfets*

Undoped devices, such as heterojunction-insulated-gate field-effect transistors (HIGFET), can host ultrahigh quality low density two-dimensional electron system (2DES), but are nearly devoid of carriers without gating [1]. In contrast, an unbiased doped device still has carriers. Microwaves are advantageous in the study of Wigner crystals (WCs) because their conductivity vanishes at dc and they exhibit pinning modes, in which the crystal oscillates within the disorder potential. For WCs in doped samples microwave measurements have been carried out using coplanar waveguides (CPW) [2]. The CPW has a driven center conductor separated from ground planes by slots, and measures mainly the 2DES under the slots. In our devices we have placed resistive film under the CPW metal and in the slots to act as the gate. Using MOSFETS and HIGFETS we demonstrate that a CPW loaded this way by a resistive film is still sensitive to 2DES conductivity, and is hence useable for microwave spectroscopy.
[1] W. Pan, et. al., PRL 106, 206806 (2011).
[2] G. Sambandamurthy, et.al., SSC 140, 100-106 (2006).