Molecular tuning of quantum Hall edge states H.A. Walling a , R. Artzi b , E.G. Gwinn a, * , R. Naaman b , K. Maranowski c , A.C. Gossard c a Department of Physics, UCSB, Broida Hall, Santa Barbara, CA 93106, USA b Department of Chemical Physics, Weizmann Institute, Rehovot 76100, Israel c Department of Materials Engineering, UCSB, Santa Barbara, CA 93106, USA Received 24 May 2003; accepted 29 June 2003 by A.H. MacDonald Abstract Hybrid organic/inorganic devices may find applications as sensors and in futuristic molecular-electronic devices. Here, we demonstrate molecular control of vertical transport in semiconductor superlattices in strong magnetic fields by adsorption of organic molecules onto the sidewalls of a GaAs/AlGaAs device. The molecules have identical attachment groups functionalized by end groups with different electronegativities. For magnetic fields in quantized Hall states, we find that the adsorbate substantially modifies the network of edge states that carries the electrical current. The data indicate that molecules with appropriately chosen end groups can enhance or decrease the vertical conductivity of the edge state system. q 2003 Published by Elsevier Ltd. PACS: 73.40.Hm; 73.40.Ns Keywords: A. Semiconductors; C. Quantum Hall effects Hybrid organic/semiconductor devices are the focus of recent attention for engineering of semiconductor surfaces [1], in new sensors [2] and as futuristic molecular electronic devices [3]. One way to combine the properties of molecules and semiconductors is by adsorbing molecules onto semiconductor surfaces. Studies of this subject have demonstrated substantial changes in surface electronic properties [1,4]. For example, organic adsorbates can produce chemical ‘gate’ effects by altering the conductivity of near-surface conducting channels in planar semiconduc- tor devices [5,6]. Here we study a new regime in hybrid devices, in which adsorbed molecules on the etched sidewalls of semicon- ductor mesas tune the properties of a special near-surface electronic phase that previous work had demonstrated in multilayered GaAs/AlGaAs heterostructures in strong magnetic fields [7,8]. As indicated schematically in Fig. 1(a), coupling of the one-dimensional edge states that encircle the perimeters of the quantum wells forms this edge-state network. In the conventional semiconductor structure it is difficult to change the conductivity of this surface phase. Here we present experimental results that show that the edge-state conductivity is sensitive to chemical modification of the mesa walls and therefore molecules can be used to control it. Recent years have seen extensive theoretical studies of edge states on single-layer, two-dimensional-electron gas systems (2DEGs). Experimental efforts to elucidate edge- state properties in 2DEGS have focused on relaxation of non-equilibrium edge current distributions [9–11] and on tunneling into the edge [12,13]. Numerous calculations [14–19] predict that edge state properties are sensitive to changes in boundary fields through their dependence on how rapidly the Landau levels bend at the edge. In 2DEGS, gates are commonly used to tune boundary fields, but this typically also alters the separation between edge states, so that effects due to changes in tunneling distances and effects due to changes in the edge states themselves can be difficult to distinguish. In the studies reported here of vertical transport between multiple 2DEG planes, the tunneling 0038-1098/03/$ - see front matter q 2003 Published by Elsevier Ltd. doi:10.1016/S0038-1098(03)00558-1 Solid State Communications 127 (2003) 707–711 www.elsevier.com/locate/ssc * Corresponding author. Tel.: þ1-805-893-2564; fax: þ 1-805- 893-4170. E-mail address: bgwinn@physics.ucsb.edu (E.G. Gwinn).