METALS AND MATERIALS International, Vol. 10, No. 4 (2004), pp. 351~355 Low-energy Ion Beam Treatment of α-Al 2 O 3 (0001) and Improvement of Photoluminescence of ZnO Thin Films Jong-Young Park, Young-Soo No, Byung-Jun Park, Hyun-Woo Lee, Ji-Won Choi, Jin-Sang Kim, Y. Ermakov, Seok-Jin Yoon, Young-Jei Oh, and Won-Kook Choi* Thin Film Materials Research Center, Korea Institute of Science and Technology P. O. Box 131 Cheongnyangni, Dongdaemun-gu, Seoul 136-791, Korea A low energy N ion beam impinged on a α-Al O (0001) single crystal surface in the range of fluence 5×10 /cm -1×10 /cm at room temperature. After ion bombardment, chemical bonding on the modified sap- phire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×10 /cm , only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×10 /cm induced Al-O-N bonding at around 403 eV. The occurrence of Al-N bonding was identified at ion fluence higher than 5×10 /cm at 396.6 eV. II-VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al-O-N bonding only, and both Al-O-N and Al-N bonding showed a significant reduction of the peak related to deep-level defects in pho- toluminescence. These results are explained in terms of the formation of Al-N and Al-O-N layers and relaxation of the interfacial strain between Al O and ZnO. Keywords: ZnO thin film, low-energy ion beam, α-Al O (0001), Al-N, photoluminescence 1. INTRODUCTION II-VI ZnO material has been extensively investigated [1-3] owing to its strong similarity, and even superiority, to III-V GaN and related nitride compounds (AlN, InN). ZnO has the same wurzite crystal structure as GaN and a very close opti- cal band gap of E g =3.37 eV at room temperature. Moreover, in particular, it has very large excition binding energy 59 meV at room temperature, which is larger than that of GaN (28 meV) and ZnSe (20 meV) [4]. Therefore, it is strongly anticipated that II-VI ZnO material will be appropriate for efficient exci- tonic optical devices with high oscillation strength. Similar to GaN, there is a large lattice misfit 18 % between ZnO and on c-Al 2 O 3 (1000). In the case of GaN growth, a high quality GaN epilayer requires the deposition of a buffer layer grown at low temperature. Prior to buffer layer growth, nitridation of a single crystal substrate has generally been adopted for the growth of high quality in the GaN epilayer [5,6]. The nitridation of the sapphire surface has been mostly carried out using N 2 or NH 3 plasma with substrate heating. Recently, surface treatment by a H 2 /N 2 plasma mixture was found to generate an oxygen deficient sapphire layer [7]. Surface treatment also improved the overgrown GaN by reducing the density of dislocations. In addition, a few tens and keV energy N 2 + ion beam irradiation have been reported to induce nitrodegn-related chemical bonding such as Al-N and Al-O-N [8,9]. In this study, a very low energy ion beam (LIB) 175 eV with high flux was irradiated to make a functional group of Al-O-N and Al-N on a sapphire single crystal surface at room temperature. The optical properties of the overgrown ZnO thin film on the modified surface are then discussed in con- junction with the contents of induced chemical bonding. 2. EXPERIMENTAL PROCEDURE Prior to the growth of ZnO, α-Al 2 O 3 (1000) single crystal- line substrates were pre-treated by two different methods, respectively. In the first, the surface was etched by a solution of H 2 SO 4 :H 3 PO 4 =3:1. This method is a kind of conventional This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24 ~ 27, 2003. *Corresponding author: wkchoi@kist.re.kr