Low Ohmic Contact Resistance of GaN by Employing XeCl Excimer Laser
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C3.52.1
Low ohmic contact resistance of GaN by employing XeCl excimer laser
Seung-Chul Lee, Jin-Cherl Her, Sang-Myun Han, Kwang-Seok Seo and Min-Koo Han School of Electrical Engineering(#50), Seoul National University, Seoul, 151-742, Korea Phone : +82-2-880-7254, Fax : +82-2-875-7254, e-mail:[email protected] ABSTRACT We have investigated a new method by which selective high doping concentration of GaN can be obtained using XeCl excimer laser and presented low ohmic contact resistance fabricated by the proposed method. We have irradiated silicon film deposited by sputtering on GaN using XeCl excimer laser and formed ohmic contact on the region irradiated by laser. Ohmic contact resistance by laser doping process was effectively reduced to 0.27 ohm-mm while 0.66 ohm-mm was measured in ohmic contact by conventional method. We have verified that silicon is diffused into GaN by high laser energy during laser irradiation through SIMS analysis and ohmic contact resistance is reduced due to increase of doping concentration under ohmic contact region. INTRODUCTION Gallium Nitride (GaN) is a promising material for high temperature, high power and high frequency applications such as MESFETs, MODFETs and LEDs due to its wide band-gap properties. However, it is well known that ohmic contact resistance of GaN is rather high compared with widely used semiconductor materials, such as Si and GaAs. Recently, many researches have been reported to obtain low ohmic contact resistance and methods for low ohmic contact resistance are the main issue for fabrication of GaN device because low ohmic contact resistance is essential for improving electrical characteristics of GaN devices [1,2]. Several metal systems have been attempted for attaining low ohmic contact resistance and metal systems based on Ti/Al have been widely used [3]. Metal contacts containing Ti/Al have displayed low ohmic contact resistance because Ti reacts with N in GaN to form TiN layer during high temperature annealing and increase of n-vacancy in GaN has resulted n+ GaN layer at the surface, enabling easy electron tunneling [4]. And various surface treatment methods have been reported such as using ICP etch and chemical treatments for increasing the n-vacancy on the surface [5,6]. Ohmic contact resistance is strongly dependent on doping concentration because the tunneling process is more dominant at high doping levels [7]. Therefore, low ohmic contact resistance can be easily obtained on highly doped GaN. Because undoped GaN layer is used for low leakage current and
Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 02 Aug 2017 at 02:04:15, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-764-C3.52
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high breakdown voltage for some electrical applications such as rectifier and HEMT, electrical characteristics of the device are poor due to high ohmic contact resistance. So, selective doping method under ohmic contact is more effective on undoped
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