Gate-Induced Carrier Delocalization in Quantum Dot Field Effect Transistors

We study the low temperature resistance and magnetotransport of high-mobility indium-doped CdSe quantum dot (QD) field effect transistors [1]. Low temperature resistance measurements show a characteristic dependence of $R(T)=R_0 \exp{(T_0/T)^p}$ with $p=2/3$, consistent with a recent model based on Coulomb gap variable range hopping plus thermal broadening. We show that using the gate bias $V_G$ to accumulate electrons in the QD channel increases the ``localization product'' $\kappa a$ (localization length $a$, dielectric constant $\kappa$), as expected for Fermi level changes near an Anderson mobility edge. Under any reasonable assumptions, $a$ increases significantly beyond the QD diameter as gate bias is applied. Magnetoresistance (MR) measurements display both positive and negative MR contributions that vary with $V_G$ and $T$. For each $V_G$, we observe a universal negative MR lineshape for higher temperatures ($T > 20$K) that scales as $T^{-4/3}$, consistent with Zeeman MR for $p=2/3$ with a gate bias-modulated mobility gap ($\Delta \varepsilon$).\\[4pt] [1] Turk, \textit{et al.}, Nano Lett., 14, 5948 (2014)