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L3.52.1

High-Spatial-Resolution Cathodoluminescence Measurement of InGaN Hisashi Kanie, Hiroaki Okado, Takaya Yoshimura Dept. of Applied Electronics, Tokyo Univ. of Science, Noda, Chiba, 278-8510, JAPAN. ABSTRACT This paper described observation of cathodoluminescence (CL) of microcrystalline InGaN bulk crystals under a scanning electron microscope (SEM) with a high-spatial-resolution (HR) CL measuring apparatus. HR-CL spectra from facets of InGaN crystals vary from facet to facet and are single peaked. Histogram analysis of the CL peak positions of HR spectra from the facets of the crystals in the area scanned during a low-resolution CL measurement shows a two-peaked form with comparable peak wavelengths. The diffusion length of a generated electron- hole pair or an exciton from the recombination centers with a higher-energy-level state to that with a lower state is estimated to be 500 nm at the longest by the comparison of two monochromatic HR-CL images of adjoining facets. INTRODUCTION InGaN active layers play an important role in a high efficiency light emitting diode ranging from violet to amber, however, its microscopic structure of luminescence center is not well understood yet [1,2]. Because almost all the samples studied are epilayers grown by metal organic chemical vapor deposition stresses within them caused by the large lattice misfit between an epilayer and a substrate modulate luminescence properties through piezoelectric field or band gap modulation. As we synthesize free standing and stress free microcrystalline InGaN [3], we study luminescence properties of InGaN without a nuisance of stresses or piezoelectric field. When we measure photoluminescence we often observed two peaked spectra. As we use a laser the excitation beam diameter of the laser is 1 mm a measured emission band is an integration of each emission band of the crystals under excitation. The intensity profile of the band may be explained by a summation of the product of the bulk density of the crystals showing a certain emission band in the observed area and the intensity of the band. As we can probe with an electron beam with a diameter of subnanometers for CL measurement, we observe CL properties for GaN microcrystals. From HR-CL images dark lines running in the or directions from a (0001)

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basal plane of GaN microcrystals are observed [4]. The dark lines terminated on the surface of {11-2x} or {1-10y} facets as dark spots. Although there is few report which associated the CL dark lines with threading dislocations [5], these dark lines are assigned to threading dislocations in GaN crystals, because their crystallographic orientation have the feature of the threading dislocation and density of the dark spots is comparable to that of the threading dislocation [4]. This paper describes the CL spectra from each facet of InGaN microcrystals and CL mapping images studied under the HR-CL SEM at room temperature. EXPERIMENT InGaN micorcrystals were grown by a two-step method described in Ref. 3. In the first step, GaN microcrystal