Review of Facet Controlled Epitaxial Lateral Overgrowth (FACELO) of GaN via Low Pressure Vapor Phase Epitaxy
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Review of Facet Controlled Epitaxial Lateral Overgrowth (FACELO) of GaN via Low Pressure Vapor Phase Epitaxy Kazumasa Hiramatsu and Hideto Miyake Dept. of Electrical and Electronic Engineering, Mie Univ., 1515 Kamihama, Tsu 514-8507, ABSTRACT Facet structures of GaN grown by epitaxial lateral overgrowth (ELO) via low pressure-metalorganic vapor phase epitaxy (LP-MOVPE) are controlled by growth conditions such as reactor pressure and growth temperature, where this technique is called FACELO (Facet Controlled ELO). The mechanism of the morphological change is discussed based on stability of the surface atoms. The propagation mechanism of the threading dislocations for the different GaN facet structure is also investigated. The distribution and density of the threading dislocations are observed by the growth pit density (GPD) method. Two typical models employing the FACELO are proposed; in one model, the dislocation concentrates only on the window area and, in the other model, only in the coalescence region in the center of the mask. In the latter model, the dislocation density is dramatically dropped to the order of 105-6 cm-2 with good reproducibility.
INTRODUCTION In the field of III-Nitrides semiconductors, selective area growth (SAG) and epitaxial lateral overgrowth (ELO) via metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) are promising techniques to obtain a high-quality epitaxial layer with low threading dislocation density and to fabricate various kinds of structures such as pyramids, wires, and dots. Firstly, wurtzite SAG GaN on line patterns [1] and dot patterns [2] were obtained by using SAG technique. This structural control technique has been applied to field emitters [3, 4], waveguides [5], facet lasers [6] and low dimensional quantum structures [7]. Usui et al. [8] and Nam et al. [9] applied the ELO technique to GaN and achieved a low dislocation density of the order of 107 cm-2. Therefore, the ELO GaN layer have much contributed to improving device performance such as LDs with a long life time [10] and UV detectors with a low reverse current density [11]. It is indispensable to aim at lower dislocation density in order to improve device performance of electronic devices as well as optical devices further. Several ELO technologies such as FIELO (Facet Initiated ELO) technique [8], PENDEO epitaxy [12], utilization of other masks as tungsten [13, 14], and multiple low temperature intermediate layer technique [15] were proposed. Recently, it was found that two-step ELO growth of GaN is a useful technique to improve crystalline quality of the ELO GaN through the facet control [16, 17]. Hereafter, we call this technique FACELO (Facet Controlled ELO). It is based on the control of GaN structures by changing growth conditions during the ELO process. The GaN structures using SAG and/or ELO have been controlled by mask size [1], mask direction [1, 9, 18-20], mask material [13, 14], mask fill factor [21], growth temperature [2, 22- 24], reactor pressure [24], flow rate of source [2
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