Molecular-beam epitaxy on shallow mesa gratings patterned on GaAs(3 1 1)A and (1 0 0) substrates Q. Gong a , R. No ¨tzel b,* , H.-P. Scho ¨nherr a , K.H. Ploog a a Paul-Drude-Institut fu ¨r Festko ¨rperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin, Germany b COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Abstract We report on the morphology and properties of the surface formed by molecular-beam epitaxy on shallow mesa gratings on patterned GaAs(3 1 1)A and GaAs(1 0 0). On GaAs(3 1 1)A substrates, the corrugated surface formed after GaAs growth on shallow mesa gratings along ½01 1 is composed of monolayer high steps and (3 1 1)A terraces. These pattern induced steps which are different on opposite slopes play an important role in InAs growth on this novel template leading to distinct lateral modulation of the island distribution. On GaAs(1 0 0) substrates, growth on shallow mesa gratings along [0 1 1], [0 1 0] and ½01 1 is drastically sensitive to the pattern direction due to the difference of steps along [0 1 1] and ½01 1. # 2002 Elsevier Science B.V. All rights reserved. PACS: 81.15.Hi; 68.55.Jk; 81.05.Ea Keywords: Molecular-beam epitaxy; Patterned substrate; GaAs(3 1 1)A; Mesa gratings; AFM; STM Patterned substrates have been widely utilized to epitaxially grow low-dimensional semiconductor structures [1–3]. We found recently that the evolution of the surface morphology during molecular-beam epitaxy (MBE) on shallow mesas (several tens of nanometers deep) is quite different from that on deep mesas (several micrometers deep) [4]. While facets are formed on deep mesas, stepped surfaces consisting of terraces of the original surface separated by mono- layer high steps develop after the overgrowth on shallow mesas. The resulting distinct pattern induced step arrangements laterally modify the local properties of the surface which can thus serve as a novel template for further nanostructured materials growth. The patterned GaAs(3 1 1)A and (1 0 0) substrates were prepared by using optical lithography and wet chemical etching in the H 2 SO 4 :H 2 O 2 :H 2 O solution. The as-etched substrate patterns consisted of 20 nm high periodic mesa gratings along the desired direc- tion with 2 mm mesa width. The 400 nm thick GaAs layers were grown at 620 8C for GaAs(3 1 1)A and 600 8C for GaAs(1 0 0). The GaAs growth rate was 0.39 mm/h and the V/III flux ratio was kept in the range 5–10. For one GaAs(3 1 1)A sample, 4 ML InAs were grown at 500 8C on the GaAs layer at the rate of 0.08 mm/h. The island formation was monitored by the reflection high-energy electron diffraction (RHEED) pattern changing from streaky to spotty. The character- ization of the surface morphology was carried out by atomic force microscopy (AFM) in air. Scanning tun- neling microscopy (STM) was performed in an ultra- high vacuum (UHV) multi-chamber system for a p-type Applied Surface Science 190 (2002) 480–484 * Corresponding author. Tel.: þ31-40-247-2047; fax: þ31-40-245-2277. E-mail address: r.noetzel@tue.nl (R. No ¨tzel). 0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-4332(01)00922-9