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Characterization of Inversion Domains in GaN by Electric Force Microscopy in Conjunction with Transmission Electron Microscopy and Wet Chemical Etching F. Yun, P. Visconti1,2, K. M. Jones, A. A. Baski, H. Morkoç, A. Passaseo2, E. Piscopiello2, M. Catalano1 and R. Cingolani2 Department of Physics and Electrical Engineering, Virginia Commonwealth University, Richmond, VA 1 Also with: Istituto per lo Studio di Nuovi Materiali per l’Elettronica, CNR, Via Arnesano, Lecce, Italy 2 Istituto Nazionale di Fisica della Materia, Unita’ di Lecce and Dipartimento di Ingegneria dell’Innovazione, Universita’ di Lecce, Italy

ABSTRACT Inversion domains (IDs) in III-nitride semiconductors degrade the performance of such devices, and so their identification and elimination is critical.An inversion domain on a Gapolarity samples appears as an N-polarity domain, which has a polarization reversed with respect to the rest of the surface and therefore has a different surface potential. Surface-contact-potential electric force microscopy (SCP-EFM) is an extension of atomic force microscopy (AFM) that allows imaging of the surface electrostatic potential. Previously, we established the particular mode of operation necessary to identify inversion domains on III-nitrides using a control sample. We have now studied inversion domains in GaN films grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). The existence of inversion domains was also verified by transmission electron microscopy (TEM) using multiple dark field imaging. In MOCVD grown GaN, we found predominant Ga-polarity with very low density of IDs, while in the MBE GaN, a mix polarity feature was identified. INTRODUCTION Despite enormous progress in GaN-based, short-wavelength optoelectronic devices and high-power microelectronic devices, which are insurmountable by other III-V compounds,1,2 defects still hinder the full potential of this material system. One such defect is the mixture of Ga-polarity and N-polarity domains on a sample, or IDs. Such IDs are affected by the growth technique, buffer layer type and growth rate.3 Polarity is a consequence of the uniaxial nature of GaN, where IDs are caused by the lack of a common stacking order between GaN and the substrate on which it is grown, as well as structural defects present in the film. The existence of IDs adds charge scattering associated with the flipping electric field distribution along the interface/surface. IDs have been previously studied for both MOCVD and MBE grown GaN samples by techniques such as convergent beam electron diffraction (CBED),4 multiple dark field TEM,5 and Auger electron spectroscopy. These techniques either require a high energy electron beam, or complex sample preparation. Recently, we have used SCP-EFM on a reference GaN sample6 with side-by-side Ga- and N-polarity regions to determine the EFM mode necessary to identify inversion domains. Because the induced surface potential varies locally in the vicinity of a unit cell, it will facilitate the imaging of inversion