Characterization of very low defect-density free-standing GaN Substrate Grown by Hydride-Vapor-Phase-Epitaxy.
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Characterization of very low defect-density free-standing GaN Substrate Grown by Hydride-Vapor-Phase-Epitaxy. P. Visconti
a,b
, M. A. Reshchikov, K. M. Jones, F. Yun, R. Cingolanib, and H. Morkoç
Virginia Commonwealth University, Dept. of Electrical Engineering, Richmond, VA 23284 Also with: Istituto per lo Studio di Nuovi Materiali per l’Elettronica, CNR, 73100, Lecce, ITALY b Also with: INFM and Dept. of Innovation Engineering, Univ. of Lecce, 73100, Lecce, ITALY
a
J. Jasinski, W. Swider, and Z. Liliental-Weber Lawrence Berkeley National Laboratory, Berkeley, CA 94720
S. S. Park and K. Y. Lee Samsung Advanced Institute of Technology, P.O.Box 111, Suwon, Korea, 440-600
ABSTRACT Structural, electrical and optical properties of free-standing 200-µm thick GaN films grown by hydride vapor phase epitaxy (HVPE) have been investigated. After laser lift-off, the GaN substrates were mechanically polished on both Ga and N-sides and dry etched only on the Gaside to obtain a smooth epi-ready surface. Hot H3PO4 chemical etching on both surfaces was used to reveal the defect sites, which appeared as hexagonal pits. The etched surfaces were then examined by atomic force microscopy. A few seconds of etching was sufficient to smooth the Nface surface and produce etch pits with a density of ≈ 1x107 cm-2. In contrast, a 50 minute etching was needed to delineate the defect sites on the Ga-face which led to a density as low as 5x105 cm-2. From plan-view and cross-sectional transmission electron microscopy (TEM) analysis, we have estimated that the dislocation density is less than about 5x106 cm-2 and ≈ 3x107 cm-2 for the Ga and N-faces respectively. The full-width at half-maximum (FWHM) of the symmetric (0002) X-ray diffraction rocking _ curve was 69 and 160 arcsec for the Ga and N-faces, respectively. That for the asymmetric (1014) peak was 103 and 140 arcsec for Ga and N-faces, respectively. Hall measurements demonstrated very high mobility (1100 and 6800 cm2/V⋅s at 295 and 50 K, respectively) and very low concentration of donors (2.1x1016 cm-3) and acceptors (4.9x1015 cm-3). In the photoluminescence (PL) spectrum taken at 10 K, a rich excitonic structure has been observed with the highest peak attributed to the exciton bound to neutral shallow donor (BDE). The FWHM of the BDE peak was about 1.0 meV on the Ga face before and after hot chemical etching, whereas that on the N-face decreased from about 20 to 1.0 meV after chemical etching owing to the removal of the surface damage originated from the mechanical polishing. INTRODUCTION Recent developments in blue light emitting diodes, lasers, UV detectors, and hightemperature and high power transistors utilizing the III-nitride materials have led to intense demands on the quality of nitride semiconductors [1]. For high performance and longevity, devices require material with low extended and point defect density. Nitride semiconductors have been deposited by hydride vapor phase epitaxy (HVPE), organometallic vapor phase epitaxy (OMVPE) and by molecular beam epitaxy (MBE) on many
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