Microstructural Defects in Mg-doped AlGaN Layers Grown by Metalorganic Chemical Vapor Deposition
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Microstructural Defects in Mg-doped AlGaN Layers Grown by Metalorganic Chemical Vapor Deposition Hyung Koun Cho and Gye Mo Yang1 Department of Metallurgical Engineering, Dong-A University, Hadan-2-Dong 840, Saha-gu, Busan, 604-714, KOREA; 1 Department of Semiconductor Science & Technology and Semiconductor Physics Research Center, Chonbuk National University, Duckjin-Dong, Chunju 561-756, Korea ABSTRACT We have investigated the formation of inversion domain boundaries in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 µmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al0.13Ga0.87N layers grown with the low Mg source flow rate, the IDBs in the Al0.13Ga0.87N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180o rotation of pyramidal defects within the same AlGaN layer. Therefore, We found that the Mg source flow rate affects significantly the dislocation density, the type of IDBs, and the shape of pyramidal defects in AlGaN layers. INTRODUCTION For good photon and current confinement of GaN based devices, a low aluminum (Al) composition AlGaN cladding layer is used in the actual InGaN/GaN multiple quantum well (MQW) light emitting diode (LED) and laser diode (LD) structures [3]. Also, AlGaN layers as the first layer grown on sapphire substrates without underlying GaN layers, which can avoid the generation of cracks, can be applied as wide-bandgap windows and buffer layers in AlGaN/GaN optoelectronic devices [1]. Planar defects such as stacking fault, inversion domain boundary (IDB), and stacking mismatch boundary are observed in GaN layers grown on sapphires, in addition to threading dislocations [2]. Two typical types of IDBs have been observed in GaN layers and AlGaN/GaN superlattice structures grown on sapphire substrates [3-5]. The polarity of films is inverted at these domains. It has been reported that the control of the polarity greatly affects the optical and structural properties of LED and LD devices [6]. In this work, we observed the shape of IDBs in Mg-doped Al0.13Ga0.87N layers using TEM.
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EXPERIMENTAL DETAILS Al0.13Ga0.87N layers were grown on c-plane sapphire substrates in a low-pressure MOCVD reactor. Trimethylgallium, trimethylaluminum, ammonia, silane (SiH4), and biscyclopentadienylmagnesium (Cp2Mg) were used as the source materials for Ga, Al, N, Si, and Mg, respectively. The Al0.13Ga0.87N layers were grown at 1100 oC after growing the GaN nucleation layers of about 25 nm thickness at 560 oC under the same growth conditions except for the dopant flow rate. The Cp2Mg flow rate in Al0.13Ga0.87N layers were changed from 0 µmol/min (undoped) to 3.172 µmol/min, respectively. In order to characterize the IDB formation in Al0.13Ga0.
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