High Resistivity GaN Formed by Ion Implantation
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High Resistivity GaN Formed by Ion Implantation Jun Kudo, Yuji Hishida, Masanori Watanabe, Tomoaki Hatayama1, and Takashi Fuyuki1 Ion Engineering Research Institute Corporation, Hirakata, Osaka 573-0128, Japan 1 Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan ABSTRACT Advanced high frequency devices using GaN-based semiconductor require the technology to form high resistivity regions with high thermal stability to electrically isolate the active elements from surroundings, as well as from the underlying substrate. The present paper describes the preparation of thermally stable, high resistivity GaN layers by ion implantation. It was confirmed that C or Zn implantation yielded high resistivity layers. In particular, Zn implantation yielded the layers with resistivity on the order of 1010 cm, which could be sustained at temperatures as high as 1000 . INTRODUCTION High frequency electron devices using compound semiconductors require the formation of high resistivity regions for electrical isolation of the active elements from surroundings, as well as from the underlying substrate. In GaN-based devices, though ion implantation of N, He, Ti, O, Fe, Cr etc. has been used for the former purpose, the resistivity of the implanted layers and its thermal stability were not always sufficient [1], [2], [3]. In particular, future miniaturization and integration seem to necessitate the technology which provides higher resistivity, and also the stability at high temperatures during device fabrication processes. The present paper describes the preparation of thermally stable, high resistivity GaN layers by implantation of Zn or C ions. The resistivity of Zn or C implanted layers and its stability at high temperatures are compared with those of the layers formed by N implantation. EXPERIMENTAL DETAILS The sample structure used in this study is depicted in Figure 1. Zn, C or N ions were 3-step implanted to a Si-doped epitaxial GaN layer with 41018 cm-3 donor concentration and 0.6 m thick, grown on the undoped GaN/AlN/sapphire substrate. The implantation conditions of these ions are listed in Table 1. Subsequently, Si ions were implanted with the dose of 21014 cm-2 at 15 keV to form a superficial contact layer. The sample was annealed at 700, 850, or 1000 for 1 min. in N2. Then, a Ni/Ti layer was EB-evaporated and patterned by chemical etching, and the exposed GaN surface was sputter etched in Ar plasma to remove the Si implanted superficial layer. The sample was finally annealed at 600 for 30 sec in N2. I-V characteristics of these samples were measured to evaluate the effects of the implanted ions and post annealing on resistivity. Measurements were made between the center and the surrounding circular electrodes from room temperature to 170 . Since the sheet resistance of Si-doped epitaxial layer below the implanted layer is as low as 200 /sq, the current flows through the path (a) - (c) - (b), as shown in Figure 1. It should also
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be noted that the current flow on the GaN surface exposed by Ar sput
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