Superlattices and Microstructures, Vol. 4, No. 415, 1988 515 QUANTUM TRANSPORT IN QUASI-ONE-DIMENSIONAL GaAs-AlxGal_xAs HETEROSTRUCTURE DEVICES A.M. Chang, G. Timp, R.E. Howard, R.E. Behringer, P.M . M ankisw ich, I.E. Cunningham, T.Y. Chang. and B. Chclluri. AT&T Bell Lmboratories. Room 4C-428. Holmdcl. NJ 07733 (Received August 17,1987) We study quantum transport properties of narrow GaAs-AlxGa k As wires and rings made by electron beam lithography. At low tempera res, clear signatures of Aharonov-Bohm quantum interference effects are observed due to the application of a perpendicular magnetic field. The ring devices show large amplitude (-5%) resistance oscillations periodic in magnetic flux penetrating the ring, which diminish in amplitude above -3kG. The wire devices show aperiodic resistance fluctuations as large as lOO%, which persist into the quantum Hall regime. The large amplitudes observed result from the small number of transverse channels occupied below the Fermi level. 1. Introduction Advances in technology and basic research often go hand in hand. The invention of electron beam lithography and plasma etching techniques has made possible the fabrication of SiMOSFET and normal metal devices on the micron- submicron scale. These devices have enabled physicists to study fundamental properties of quantum transport arising from electron interference effects requiring phase coherence on the size scale of a device,1’6 and low temperature resistance switching phenomenon due to the filling and emptying of a single trap state.’ Recently, we have succeeded in fabricating quasi l-d GaAs- AlGaAs heterostructure devices of con&cting width, W, X00-2OOOA, by electron beam lithography and reactive ion etching techniques.8-10 These devices are unique in allowing us to access previously unaccessible or marginally accessible regimes of low transverse channel conduction (<lo), long elastic scattering length, l,> W, and the quantum limit in a magnetic field of oEr= pB> 1, where the quantum Hall effect can be observed. Here o,=eB/m*c is the cyclotron frequency, r the scattering time, and TV the mobility. In this paper, we describe our study on the transport properties of wire and ring geometries, made from both high and low mobility materials. We observe a variety of interesting quantum interference effects at low temperatures (<lK), 0749-6036/88/040515+ 06 $02.00/O with the application of a magnetic field perpendicular to the heterojunction interface. In ring devices, we observe large amplitude, resistance oscillations periodic in he/e magnetic flux penetrating the enclosed area of the the ring.11J2 In wires, we find aperiodic resistance fluctuations which can be as large as lOO%, when the voltage probe separation, $, is made small (ld-1J.s Whereas the periodic ring oscillations disappear above -3kGauss. the aperiodic fluctuations persist well into the quantum limit. Surprisingly, these aperiodic fluctuations often contain a distinct component which is periodic over a field range of several kGauss. At low magnetic fields, the observed results are manifestations of the Aharonov-Bohm (AB) quantum interference effect. At high fields, the fluctuations may arise from a combination of quantum percolation and AB interference effects. The periodic ring AB effect13*14and aperiodic wire AB effect13J6 in narrow GaAs-AlGaAs heterostructure devices have also been observed by other workers. 2. Fabrication The devices are fabricated by electron beam lithography and reactive ion etcbing.g First, a lead frame with a 50pmx50Fm pedestal in the center is defined by photolithography on a GaAs-AlGaAs crystal. Indium contacts are alloyed to the leads, followed by electron beam patterning with the patterns shown in figure 1. The lithographic line 0 1988 Academic Press Limited