Growth of epitaxial AlN ®lms on (Mn,Zn)Fe 2 O 4 substrates by pulsed laser deposition 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 havegrown AlN on (Mn,Zn)Fe 2 O 4 substrates by pulsed laser deposition (PLD) and investigated their structural properties using high resolution X-ray diffraction (HRXRD), re¯ection high energy electron diffraction (RHEED), and atomic force microscopy (AFM). We have observed the transition of the RHEED pattern from sharp streaks into clear spots at the early stage of the ®lm growth, which indicates that the growth mode of AlN changed from the two-dimensional mode to the three- dimensional mode due to the stress buildup. RHEED and XRD observations have revealed that hexagonal AlN (0 0 0 1) grows on (Mn,Zn)Fe 2 O 4 (1 1 1) with the in-plane epitaxial relationship of [1 1 2 0]AlN//[0 1 1](Mn,Zn)Fe 2 O 4 . The lattice mismatch for this alignment is calculated to be 6%. The FWHM value of the AlN (0 0 0 2) X-ray rocking curve is as low as 77 arcsec, which indicates that the density of the threading screw dislocations in the AlN ®lm is quite low. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Pulsed laser deposition; AlN; (Mn,Zn)Fe 2 O 4 1. Introduction Recent advances in the epitaxial growth techniques of the group III-nitrides have led to the success in the applications of short wavelength optical devices such as blue light emitting diodes and laser diodes [1±3]. Among the group III-nitrides, aluminum nitride (AlN) shows a direct band gap of 6.2 eV at 300 K, a high melting point (3273 K), and a high thermal conducti- vity (285 W/mK). These properties make AlN a pro- mising candidate as a material for optoelectronic devices and high temperature electronic devices. It is obvious that the crystalline quality of the AlN ®lms is inherently important for these applications. Various substrates with small lattice mismatches have been tested for epitaxial growths of AlN ®lms. However, most of them resulted in the formation of AlN with poor crystallinity. It is quite reasonable to believe that this problem mainly stems from nitridation reaction at the substrate surfaces because conventional AlN growth techniques (MOCVD or MBE) utilize highly reactive nitrogen sources such as an NH 3 gas or N 2 plasma, which cause nitridation of the substrate sur- faces just before the epitaxial growth. This limits the substrates for the epitaxial growth of AlN to chemi- cally stable materials such as Al 2 O 3 . Since the lattice mismatch between AlN and Al 2 O 3 is very large (13%), the AlN ®lms contain a large number of defects. To improve the crystalline quality of AlN epitaxial ®lms, the use of lattice matched substrates is required. We have recently shown that the use of the pulsed laser deposition (PLD) technique for the epi- taxial growth of group III-nitrides is advantageous over the conventional growth techniques in that it does Applied Surface Science 197±198 (2002) 486±489 * Corresponding author. Tel.: 81-3-5841-7192; fax: 81-3-5841-8744. 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(02)00376-8