Applied Surface Science 256 (2010) 7434–7437 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc GaAs surface passivation by plasma-enhanced atomic-layer-deposited aluminum nitride M. Bosund ∗ , P. Mattila, A. Aierken, T. Hakkarainen, H. Koskenvaara, M. Sopanen, V.-M. Airaksinen, H. Lipsanen Department of Micro and Nanosciences, Aalto University School of Science and Technology, P.O. Box 13500, FI-00076 Aalto, Finland article info Article history: Received 19 March 2010 Received in revised form 24 May 2010 Accepted 24 May 2010 Available online 1 June 2010 Keywords: GaAs passivation Plasma-enhanced ALD Aluminum nitride abstract A low-temperature passivation method for GaAs surfaces is investigated. Ultrathin AlN layers are deposited by plasma-enhanced atomic-layer-deposition at 200 ◦ C on top of near-surface InGaAs/GaAs quantum well structures. A significant passivation effect is seen as shown by up to 30 times higher photo- luminescence intensity and up to seven times longer lifetime compared to uncoated reference samples. The improved optical properties are accompanied by a redshift of the quantum well photoluminescence peak likely caused by a combination of the nitridation of the GaAs capping layer and a surface coupling effect. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Gallium arsenide based technology is widely used in opto- electronics and also in certain integrated circuits applications. However, the development of GaAs devices is partly limited by surface recombination and Fermi level pinning on the GaAs surface, due to which structures near the surface are unsta- ble and suffer from a gradual degradation from air and light exposure. Several in situ passivation methods based on ultrathin GaN [1,2], AlN [3] and InP [4] layers grown by metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE) have been reported. However, the process temperature in these methods has been over 400 ◦ C which may be too high for many applications. Nitrogen plasma irradiation methods to produce a thin GaN layer on GaAs by MBE have also been tried. Good results were achieved when the nitridation temperature was above 450 ◦ C [5]. Also liq- uid solution based passivation methods have been reported but the solution passivated GaAs surface suffers from a gradual degra- dation from air and light exposure [6,7]. Atomic-layer-deposited TiN [8] has also been tested for GaAs passivation. However, better passivation efficiency is achieved in this study at lower deposition temperature. In this paper a low-temperature passivation method for GaAs surfaces is reported. An ultrathin (0.1–10 nm) AlN layer is deposited ∗ Corresponding author. Tel.: +358 9 470 23126; fax: +358 9 470 23128. E-mail address: Markus.Bosund@tkk.fi (M. Bosund). by plasma-enhanced atomic-layer-deposition (PEALD) at 200 ◦ C on top of a near-surface InGaAs/GaAs quantum well structure. Good uniformity, easy scale-up for larger areas, and the low process temperature enabled by the nitrogen/ammonia plasma make the presented method a promising ex situ passivation technique. 2. Experimental details A 4.3-nm-thick In 0.21 Ga 0.79 As/GaAs near-surface quantum well (NSQW) was grown on a GaAs (1 0 0) substrate in a horizontal MOVPE reactor at atmospheric pressure using hydrogen as the car- rier gas. Tertiarybutylarsine (TMAs), trimethylgallium (TMGa) and trimethylindium (TMIn) were used as precursors for arsenic, gal- lium and indium, respectively. The NSQW was sandwiched by a 125-nm-thick buffer and 4 or 6-nm-thick GaAs capping layer. After MOVPE growth the NSQW sample was cleaved into several pieces, one was kept as a reference while the others were used in the passivation experiments. Aluminum nitride passivation layers were grown by a Beneq TFS-500 capacitive plasma ALD reactor. The schematic picture of the equipment and the precursor pulsing technique are shown in Fig. 1. Trimethylaluminum (TMA) and ammonia (NH 3 ), enhanced by nitrogen plasma, were used as precursors while nitrogen (N 2 ) was used as the carrier gas. TMA was pulsed for 0.8 s and NH 3 for 10 s while the purge times after the TMA and NH 3 pulses were 3 and 1 s, respectively. The growth temperature of the AlN layers was 200 ◦ C. Plasma power was set to 50 W and turned on before the NH 3 pulse and off before TMA pulse in every cycle. Before the growth 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.05.085