Journal of Crystal Growth 301–302 (2007) 158–162 Growth of (In,Ga)As/(Al,Ga)As quantum wells on GaAs(1 1 0) by MBE R. Hey à , A. Trampert, U. Jahn, O.D.D. Couto Jr., P. Santos Paul Drude Institut fu ¨r Festko¨rperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany Available online 20 December 2006 Abstract The structural and optical properties of (In,Ga)As/(Al,Ga)As quantum wells grown on GaAs(1 1 0) by conventional molecular beam epitaxy as well as by migration-enhanced epitaxy are studied by low-temperature photoluminescence (PL), cathodoluminescence (CL), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The quality of GaAs/(Al,Ga)As quantum wells (QWs) allows to detect spin transport mediated by surface acoustic waves over distances up to 65 mm with spin lifetimes of about 22 ns. For (In,Ga)As/GaAs QWs, the accumulated strain due to the increase of the In mole fractions or the well thicknesses degrades the structural perfection more dramatically in structures with (1 1 0)-orientation than in structures with (0 0 1)-orientation. The quality of (In,Ga)As wells is remarkably improved by migration-enhanced epitaxy. r 2007 Elsevier B.V. All rights reserved. PACS: 68.37.Lp; 78.66.Fd; 78.67.De; 81.15.Hi Keywords: A1. Low-dimensional structures; A3. Molecular beam epitaxy; B2. Semiconducting III–V materials 1. Introduction Long spin lifetimes are beneficial for the manipulation and transport of spins in semiconductor heterojunctions. GaAs/(Al,Ga)As-quantum wells (QWs) with (1 1 0)-orien- tation are promising for spintronic application since their spin relaxation times remarkably exceed the ones of their (0 0 1) counterparts [1]. However, the missing variety of surface reconstructions [2] disables the precise in situ control of growth parameters by reflection high-energy electron diffraction and, hence, aggravates the growth of III–V heterojunctions on GaAs(1 1 0). Furthermore, for minimizing surface faceting [3], the growth on GaAs(1 1 0) substrates at lower temperatures and higher V–III flux ratios [4–6], compared to GaAs(0 0 1), impairs the optical properties of these QWs. An improvement of the structure perfection is achievable by migration-enhanced epitaxy (MEE) [7–9]. In addition, a reduction of the surface step density in QWs by growth interruptions for surface annealing is obtained [10]. Here, we report on GaAs/ (Al,Ga)As- and (In,Ga)As/GaAs single-quantum wells (SQW) grown on GaAs(1 1 0) substrates under optimised molecular beam epitaxy (MBE) and MEE conditions. Besides their smaller band gaps, (In,Ga)As/GaAs-QWs are very attractive for spintronics applications because their higher g-factor allows the manipulation of spins using smaller external magnetic fields. As potential fluctuations in the QW are detrimental to spin transport mediated by surface acoustic waves (SAW), we focus on the improve- ment of (In,Ga)As/GaAs-SQWs and their interface quality. 2. Experimental procedure Before the growth, each GaAs(1 1 0) substrate was smoothed after oxide desorption by the deposition of 10 nm of GaAs in the MEE mode. GaAs/(Al,Ga)As-QWs were grown by MBE whereas (In,Ga)As/GaAs-QWs were grown by MBE and MEE. The MEE procedure for the growth of (In,Ga)As consisted of a 1.3 s instantaneous supply of In and Ga, followed by a 4 s supply of As 4 and a 10 s growth interruption. The growth rates for the QWs were about 220 and 560 nm/h for MBE and MEE, respectively. Even in the MBE mode, growth interruptions were introduced at each QW interface to perform a 1 min annealing at 600 1C [9]. For each structure, the growth ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2006.11.291 à Corresponding author. Tel.: +49 30 20377 354; fax: +49 30 20377 201. E-mail address: hey@pdi-berlin.de (R. Hey).