Enhanced Light Emission at Self-assembled GaN Inversion Domain Boundary
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Enhanced Light Emission at Self-assembled GaN Inversion Domain Boundary Mei-Chun Liu1, Yuh-Jen Cheng,1 Jet-Rung Chang,2 and Chun-Yen Chang2 1 Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan 2 Institute of Electronics, National Chiao Tung University, 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan ABSTRACT We report the fabrication of GaN lateral polarity inversion heterostructure with self assembled crystalline inversion domain boundaries (IDBs). The sample was fabricated by two step molecular-beam epitaxy (MBE) with microlithography patterning in between to define IDBs. Despite the use of circular pattern, hexagonal crystalline IDBs were self assembled from the circular pattern during the second MBE growth. Both cathodoluminescent (CL) and photoluminescent (PL) measurements show a significant enhanced emission at IDBs and in particular at hexagonal corners. The ability to fabricate self assembled crystalline IDBs and its enhanced emission property can be useful in optoelectronic applications. INTRODUCTION III-Nitride semiconductors, in particular GaN, have attracted great research interests in past few years due to their promising applications for UV to blue optoelectronic devices [1]. One of the important properties of wurtzite GaN is its strong spontaneous and piezoelectric polarization, which can induce surface charges and create large internal electric field in the film. This electric field can strongly affect the electrical and optical properties of GaN based devices [2, 3]. It can reduce the electron-hole wave function overlap in quantum well devices and have adverse effect on its light emitting efficiency. The direction of internal field depends on crystal caxis orientation which is not symmetric. The c-axis crystal surface is conventionally labeled as Ga- (0001) or N-polar (000-1). Recently, there are interests in studying the physical property of inversion domain boundary between Ga- and N-polar regions. The IDB has been found to exist at microscopic scale in Ga-polar GaN thin film grown by MBE [4]. The IDB can also be created by intentionally growing lateral polarity heterostructures, where patterned Ga- and N-polar regions are laterally grown on the same substrate to form IDBs [5]. The ability to fabricate controlled polarity pattern can open up new dimension for GaN device design and applications. The IDB has been studied theoretically [6, 7], and experimentally imaged by high-resolution transmission electron microscope [4, 5], and piezoelectric force microscope [8, 9]. It was theoretically predicted that IDBs in wurtzite GaN would not have electronic states in the band gap, implying that they would not affect PL efficiency [6]. The optical property of IDB has been investigated by high resolution spatially resolved PL measurement [10]. The measurement was done at 10K low temperature and significantly brighter emission was reported at IDBs. However, the observed emission from IDB was neither spectrally nor spatially uniform. The non-uniformity could be due to the coexistence of differe
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