Thin Solid Films 396 (2001) 219–224 0040-6090/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0040-6090 Ž 01 . 01231-7 Commensurability oscillations on lateral surface superlattices with large periods A. Abd-El Mongy *, A.R. Long , E. Belal , K. Ali a, b c c Department of Physics, Faculty of Science, Helwan University, Cairo, Egypt a Department of Physics and Astronomy, University of Glasgow, Glasgow G 12 8QQ, UK b Department of Physics, Faculty of Science Aswan, South Valley University, Cairo, Egypt c Received 24 April 2000; received in revised form 31 May 2001; accepted 20 June 2001 Abstract We present for the first time, an investigation of commensurability oscillations (COs) on lateral surface superlattice devices with large periods (1 and 2 mm). The observed values of the COs positions are compared with the predicted peaks. In forward bias clear COs are observed. It is noticed that the COs have a strong dominant third harmonic content. The COs are found to vanish with increasing negative bias.  2001 Elsevier Science B.V. All rights reserved. Keywords: Superlattices; Heterostructures; GaAs y AlGaAs; Magnetoresistance; Commensurability oscillations 1. Introduction Recent advances in molecular beam epitaxy and nanofabrication techniques have generated interest in a periodically modulated two-dimensional electron gas (2DEG). It is now possible to fabricate lateral surface superlattices (LSSLs) using surface gates on very high mobility GaAs y AlGaAs heterostructures in which the electron retains its phase coherence over many periods of the superlattice. Applying a negative voltage to the superlattice gate produces a periodic modulation of charge density in the 2DEG, due to carrier depletion under the gate. This electrostatical production of a periodic potential in the 2DEG is considered the main reason for using LSSLs. A problem with any gated structure is the distance ‘d’ between the electrons in the 2DEG and the gates on the surface, which smoothes and weakens the produced potential. The smaller the lattice period wthe period of the LSSLsx, the more crucial becomes the distance (d). To overcome this limitation, the depth d was reduced (shallow structure) which * Corresponding author. E-mail address: abdelmongy@hotmail.com (A. Abd-El Mongy). allows the transfer of the potential induced by the small period lateral superlattice more accurately. In turn, the periodic potential becomes non-sinusoidal w1x. The clearest manifestation of the modulation of the 2DEG is the appearance of a series of oscillations in the low- field magnetoresistance arising from the commensura- bility between the cyclotron orbit and the period of the potential w2x. The origin of these oscillations is now well understood and most data in deep structure (the 2DEG is typical more than 100 nm underneath the surface) are described by a semiclassical model with a sinusoidal modulation potential w3x. This model allows the magnitude of the potential seen by the electrons in the 2DEG to be calculated and shows that the amplitude of the COs depends strongly on the mean free path of electrons. Also it suggests that the COs amplitude is linear with the field B, which is not found in experi- mental reality w4,5x. This discrepancy has been explained as being the result of small angle scattering specially for the higher index peaks, namely at lower B. Electrons with higher index values travel further to complete an orbit, and hence have more chance of being scattered. Paltiel et al. w6x showed that the amplitude of the COs peaks can be well understood in terms of the angular