Characterization of hetero-interfaces between group III nitrides formed by PLD and various substrates J. Ohta * , H. Fujioka, H. Takahashi, M. Oshima Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan Abstract We have grown group III nitride epitaxial films on various substrates by pulsed laser deposition and investigated structural properties of the surfaces and the hetero-interfaces using grazing incidence angle X-ray reflectivity (GIXR) and atomic force microscopy (AFM). It has been found that hetero-interfaces between PLD AlN and conventional substrates such as Al 2 O 3 and Si are quite abrupt (about 0.5 nm) probably due to a less reactive growth ambience. However, we observed a thin interfacial layer (less than 10 nm) at the hetero-interface between AlN and (Mn,Zn)Fe 2 O 4 . The surface roughness of AlN is mainly determined by the extent of the lattice mismatch. It has been also found that the roughness at the hetero-interface between GaN and AlN formed by PLD coincides with the surface roughness of the AlN layer. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Group III nitrides; GIXR; Hetero-interface 1. Introduction Group III nitrides are promising materials for optical device applications such as light emitting diodes (LEDs) and laser diodes (LDs) [1–3]. Typical thin film growth techniques for the group III nitrides have been metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). In these methods, however, the substrates are exposed to the highly reactive NH 3 or N 2 plasma ambient, which results in nitridation of the substrate surfaces just before the epitaxial growths. This limits the substrates for the epitaxial growths of the group III nitrides to chemically stable materials such as Al 2 O 3 and Si. Recently, we have found that the use of PLD for the epitaxial growth of group III nitrides allows us to use chemically less stable substrates which include (La,Sr)(Al,Ta)O 3 , (Mn,Zn)Fe 2 O 4 and SrTiO 3 [4,5]. This advantage over the conventional growth techniques such as MOCVD and MBE can be attributed to the fact that PLD growths proceed in a less reactive N 2 ambience. The use of these versatile oxide substrates enables to develop new types of devices which utilize semiconducting, magnetic, ferroelectric and superconducting properties. To develop devices with group III nitrides on these newly proposed substrates, it is necessary to charac- terize the hetero-interfaces precisely. Grazing inci- dence angle X-ray reflectivity (GIXR) is a suitable tool for this purpose because it gives information on the film thickness, density, surface roughness and abruptness of the hetero-interfaces. It is known that the accuracy of the surface and interface roughnesses determined by GIXR measurements is as good as those determined by transmission electron microscope (TEM) [6]. In this paper, we discuss the structural characteristics of the surfaces and hetero-interfaces between group III nitrides and various substrates formed by PLD based on the results of GIXR, reflection high Applied Surface Science 190 (2002) 352–355 * Corresponding author. Tel.: þ81-3-5841-7192; fax: þ81-3-5841-8744. E-mail address: ohta@sr.t.u-tokyo.ac.jp (J. Ohta). 0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-4332(01)00847-9