Structural, Morphological, Optical and Electrical Properties of Bulk (0001) GaN:Fe Wafers
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.234
Structural, Morphological, Optical and Electrical Properties of Bulk (0001) GaN:Fe Wafers M. Gaddy, V. Kuryatkov, V. Meyers, D. Mauch, J. Dickens, A. Neuber, and S. Nikishin Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX 79401 UNCLASSIFIED Distribution A: Approved for public release
ABSTRACT
Characterization of three vendor’s bulk semi-insulating GaN:Fe wafers, grown by either hydride vapor phase epitaxy or the ammonothermal method, was performed using: scanning electron microscopy, secondary ion mass spectroscopy, high resolution X-ray diffraction, cathodoluminescence, photoluminescence, and high voltage testing. Although the Fe doping level is significantly different for each growth method, both are promising for the fabrication of PCSS devices operating in the lock-on mode.
INTRODUCTION Bulk semi-insulating (0001) GaN:Fe wafers are important in the development of numerous optoelectronic devices including high voltage photoconductive semiconductor switches (PCSS) [1 – 3]. High resistivity and semiinsulating GaN:Fe films can be grown by metal organic chemical vapor deposition (MOCVD) [4, 5] and molecular beam epitaxy (MBE) [6]. However, commercially available bulk wafers are grown by either hydride vapor phase epitaxy (HVPE) [7 – 9] or the ammonothermal method (ATM) [10 – 14]. The resistivity of such wafers varies from 10 6 to 1010 Ωcm. In order to compare the properties of bulk GaN:Fe grown by both, ATM and HVPE we obtained commercially available bulk samples from three different vendors K, R, and A. Samples from vendors K and R were grown using HVPE and the sample from vendor A was grown using ATM. The structural, morphological, optical and electrical properties of these bulk GaN:Fe wafers were characterized using high resolution X-ray diffraction (XRD), scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS), cathodo- and photo- luminescence (CL &PL), and high voltage current/voltage (IV) testing. We found that both growth methods can produce high crystalline quality and high resistivity bulk GaN:Fe. However, the concentration of impurities, such as Ca, K, Na, H, C, and O, that were unintentionally incorporated during the growth varied by growth method and depth. The distribution of these impurities could be a cause of significant differences in the electrical properties of GaN:Fe wafers. EXPERIMENT AND DISCUSSION X-ray diffraction studies were performed on all samples using an X’Pert XRD (Philips) high-resolution diffractometer. Figure 1 shows the rocking curve of symmetric (002), Fig. 1a, and asymmetric (102), Fig. 1b, planes. Screw and edge dislocation densities, Ndislocation, were estimated from the FWHM of these rocking curves using [15 – 17]
N dislocation
E2
2S u ln 2 u b 2
(1)
Where b is the length of Burger vector and β is the full width at half maximum (FWHM) of (002) or (102) ω scans. Screw dislocation densities of 2.7x105, 3.1x105, and 5.9x107 cm–2 and edge disl
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