Superlattices and Microstructures, Vol. 9, No. 1, 1991 11 9 ANISOTROPIC MAGNETOTRANSPORT IN AN ANTIWIRE ARRAY INSERTED IN A GAAS HETEROSTRUCTURE K. Ensslin, S. A. Chalmers, P. M. Petroff, A. C. Gossard, and H. Kroemer Materials Department, University of California, Santa Barbara, Ca 93106 (Received 13 August 1990) An array of antiwires is prepared in GaAs/A1GaAs heterostructures by using the tilted superlattice approach. A regular two-dimensional electron gas (2DEG) is grown on a 2° off axis (100) substrate. Half a monolayer of AlAs is inserted close to the GaAs/A1GaAs interface ordering itself along the step edges. Therefore an antiwire array is formed which directly influences the envelope wavefunction of the two--dimensionalelectrons. Low temperature magnetotransport measurements with current flow parallel and perpendicular to the wires reveal a pronounced anisotropy in the magnetoresistance Pxx of the carriers. The value of Pxx/(B--0) for current flow perpendicular to the antiwires is larger than Pxxll. The anisotropy increases with increasing carrier density in agreement with the formation of Bloch bands due to the periodicity of the antiwire array. For high magnetic fields B>2T the minima of the Shubnikov-de Haas oscillations for Pxx-1-and Pxxll occur at the same fields indicating the homogeneity of the 2DEG. For low magnetic fields B=0.5T we observe a maximum in Pxx± while Pxxll stays constant. The Hall resistances Pxy ± and Pxyll are indistinguishable from each other for all ranges of B and Ns. Current transport in one-dimensional (1D) quantum wires is an interesting problem in fund.anaen _t_t_al_phyuiocsl~2 and has important implicauons on aewce appm:n v ~ . Usually a quantum wire is represented by an attractive wire-like potential which is surrounded by potential barriers in two dimensions. Here we present the interesting approach of a repulsive wire like potential which is imbedded in a two-dimensional electron gas (2DEG). This structure is promising for the investigation of lateral superlattice effects as well as confinement effects depending on the parameters of the antiwire array and the 2DEG. A si/nilar structure has been investigated by Motohisa et al. ,4 in the regime of very low magnetic fields. Our structure is realized by growing a conventional modulation-doped GaAs-A1GaAs heterostructure on a vicinal GaAs substrate, tilted by 2 ° from the (100) axis. The repulsive potential is formed by inserting half a monolayer of AlAs 4nm below the GaAs/AIGaAs interface using the step flow growth mode. In this paper we present low-temperature high- magnetic field measurements with current flow along (11) and perpendicular (.1_)to the antiwires. The longitudinal magnetoresistance Pxx shows a pronounced anisotropy Pxx± > Pxxll for all magnetic fields. For increasing bias on the front gate electrode we find an increase of the anisotropy with increasing carder density in qualitative agreement with the formation of Bloch-bands due to the periodicity of the antiwire array. The minima of the Shubnikov-de Haas (SdH) oscillations occur at the same field for both directions of current flow indicating the homogeneity and quality of our 2DEG. The carrier densities Ns deduced from the periodicity of the SdH oscillations agree nicely with the values obtained from Hall measurements. For low magnetic fields B=0.9T a maximum in Pxx J- is found while Pxxl] decreases monotonically with increasing B. This effect might be due to the formation of a lateral surface superlattice. The GaAs-A1GaAs heterostructures are ,grown by MBE with the following growth sequence: ~ a semi- insulating substrate misoriented by 2 ° from the (100) direction, 1.) a300 nm buffer layer, 2.) 4 nm of GaAs by migration enhanced epitaxy (MEE), 3.) half a monolayer of AlAs, 4.) 4 nm GaAs, 5.) 5 nm AIGaAs spaces^ 6.) ~0 nm Si-doped A10.3Ga0.7As (ND = lxl01acm -~) and 7.) a 10 nm GaAs cap layer. At T 0749-6036/91/010119+03 S02.00/0 © 1991 Academic Press Limited