Photoluminescence Study of Damage Introduced in GaN by Ar- and Kr-Plasmas Etching
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Photoluminescence Study of Damage Introduced in GaN by Ar- and Kr-Plasmas Etching Yoshitaka Nakano 1, Retsuo Kawakami 2, Masahito Niibe 3, Atsushi Takeichi 2, Takeshi Inaoka 2, Kikuo Tominaga 2 1 Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan 2 The University of Tokushima, 2-1 Minami-Josanjima, Tokushima 770-8506, Japan 3 University of Hyogo, 3-1-2 Koto, Kamigori, Ako, Hyogo 678-1205, Japan ABSTRACT We investigated, by employing a photoluminescence technique, the etching damage introduced in near-surface regions of GaN by Ar and Kr plasmas and clarified the differences between the damage characteristics of these regions for the two plasma etching cases. For Ar plasma, the shallow donor-acceptor pair emission at ~3.28 eV was significantly weakened; additionally, a broad blue luminescence band arose at approximately ~3.0 eV. In contrast, for Kr plasma under high gas pressure, we found the recovery of the damage to the same level as the asgrown crystallinity. These differences in the damage characteristics for the two plasma etching cases probably depend upon which atom (N or Ga) is preferentially etched in these cases. INTRODUCTION Gallium nitride (GaN) is a promising material for fabricating high-power, and highfrequency optoelectronic devices because of its remarkable features such as a wide band gap of 3.39 eV, a high breakdown field of 5 × 106 V/cm and a high saturation drift velocity of 2.7 × 107 cm/s [1]. Recently, GaN-based devices have been developed with advances made in plasma etching techniques [2]. However, damage introduced in GaN surfaces by plasma etchings is a critical issue, because it is closely related to the degradation of device performance [3,4]. The plasma etching of GaN, composed of Ga and N atoms, is a preferential etching process that results in the etching of specific atoms from the GaN surface. This preferential etching causes an undesirable GaN surface, as in the case of Ga- or N-rich conditions, resulting in a significant decrease in electrical activity. Recently, Kawakami et al. reported, based on theoretical calculations and X-ray photoelectron spectroscopy (XPS) analyses, that N is preferentially etched by Ar plasma and that Ga is preferentially etched by Kr plasma [5,6]. Additionally, they also reported that anomalous surface defects are formed on GaN surfaces through Ar plasma etching under high gas pressures and for a long etching time; this phenomenon is probably associated with ultraviolet (UV) irradiation from the Ar plasma onto GaN surfaces [5]. However, these issues have yet to be completely understood. Thus, to educe the potential of GaN materials, we must perform a basic investigation of the plasma-etching damage in GaN using a multifaceted approach. In this study, we investigate damage introduced in GaN near-surfaces by fundamental Ar- and Kr-plasmas etching by employing a photoluminescence (PL) technique and clarified the differences in their damage characteristics. EXPERIMENTAL
4 µm-thick Si-doped GaN films with n-type carrier concentrations of 5 × 1017
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