Using Oxide Interlayer as Passivation for Ti/n⁺-GaN Ohmic Contact to Achieve Lower Contact Resistivity

To satisfy the requirement of better device performance, the dimension down-scaling becomes the common trend of GaN devices, leading the increased ohmic contact resistance between metal and GaN to be one of the main parameters that hinders the development of device performance. Considering the band structure mismatch and Fermi level pinning effect at the ohmic contact interface, we propose an effective method of introducing oxide interlayer as ohmic contact passivation. Developing upon applying the selective-aera regrown (SAG) highly n-type doped GaN(n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-CaN) as alternative contact layer, the RTLM samples and VDP Hall test samples are prepared to extract the resistivity parameters. The specific contact resistivity of metal Ti/TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>/n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-GaN MIS structure achieves 5.25e-8 Ω.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with 2.5nm thickness TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>, which is significantly lower than the 3.49e-7 Ω.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of Ti/n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-GaN. While the Ti/AlOx/n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-GaN MIS structure exhibits Schottky contact characteristics. To investigate the origin of the results, the TEM, EDX and band structure analysis are applied to analyze the ohmic contact interface. This passivation method shows a novel way to acquire lower contact resistance for scaling GaN devices.