Achievements and Characterizations of GaN With Ga-Polarity in Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy
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ACHIEVEMENTS AND CHARACTERIZATIONS OF GaN WITH Ga-POLARITY IN RADIO-FREQUENCY PLASMA-ASSISTED MOLECULAR BEAM EPITAXY X.Q. SHEN, T. IDE, S.H. CHO, M. SHIMIZU, S. HARA and H. OKUMURA Materials Science Division, Electrotechnical Laboratory (ETL), 1-1-4 Umezono, Tsukuba, Ibaraki, 305-8568 Japan ABSTRACT Lattice polarities and film qualities of GaN grown by rf-MBE were investigated concentrating on the use of different buffer layer processes at the initial stage.
Direct
clarifying by coaxial impact collision ion scattering spectra technique, together with RHEED and chemical wet etching, were applied to identify the lattice polarity of GaN films. XRD rocking curve and photoluminescence results showed that the qualities of GaN films with Ga-polarity were dramatic improved compared to those with N-polarity.
Hall effect
measurement results indicated that the mobility of the Ga-face film was increased to one order higher (568 cm2/Vs in maximum at room temperature) than that of N-face one. INTRODUCTION Wide band-gap GaN and related III-nitride materials have attracted a great deal of attention due to their potential usefulness in optical and electronic devices. Recently, lattice polarity in III-nitride films becomes a hot topic due to its great influence on the optical and electrical properties of the films. Several techniques were applied to characterize the film polarity, such as convergent beam electron diffraction (CBED) [1], hemi-spherically scanned x-ray photoelectron diffraction (HSXPD)[2], Rutherford backscattering ion channeling[3], chemical wet etching and surface reconstruction by reflection high-energy electron diffraction (RHEED) [4], etc. Based on the results, Ga-polarity films are believed to be usually obtained by metalorganic chemical vapor deposition (MOCVD), which is known to be the most suitable technique for III-nitride growth at present. Contrary to the case of MOCVD, the lattice orientation of conventional molecular beam epitaxy (MBE)-grown sample is assumed to be mainly N-polarity [5]. In III-nitride materials, MBE-grown films usually show poor qualities compared with MOCVD-grown ones, especially concerning electrical properties. Recently, we pointed out that the growth should be done under the Ga-face mode to get high T6.22.1
film qualities in MBE [6]. Therefore, characterization and comparison of GaN films with Ga- and N-polarity are becoming interesting and important subjects. In this study, we characterized lattice polarities and film qualities of GaN grown by rf-MBE concentrating on the use of different buffer layer processes at the initial stage.
Direct
clarifying by coaxial impact collision ion scattering spectra (CAICISS) technique, together with RHEED and chemical wet etching, were applied to identify the lattice polarity of GaN films. XRD, PL and Hall-effect measurements were carried out to characterize the qualities of GaN films. EXPERIMENTAL The GaN films were grown on sapphire (0001) substrates by rf-MBE. Low temperature (LT=500oC), high-temperature (HT=700oC) GaN and AlN buffer lay
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