非故意掺杂GaN上Ti/Al/Ni/Au欧姆接触研究

基于圆形传输线模型,研究了背景载流子浓度为71016cm3的非故意掺杂GaN与Ti/Al/Ni/Au多层金属之间欧姆接触的形成。样品在N2气氛中,分别经过温度450,550,700,800,900℃的1 min快速热退火处理后发现,当退火温度高于700℃欧姆接触开始形成,随着温度升高欧姆接触电阻持续下降,在900℃时获得了最低比接触电阻6.6106O·cm2。研究表明,要获得低的欧姆接触电阻,需要Al与Ti发生充分固相反应,并穿透Ti层到达GaN表面;同时,GaN中N外扩散到金属中,在GaN表面产生N空位起施主作用,可提高界面掺杂浓度,从而有助于电子隧穿界面而形成良好欧姆接触。

Investigation of Ti/Al/Ni/Au Multilayer Ohmic Contact to Unintentional Doped GaN

In the light of circular Transfer Length Model (TLM), Ti/Al/Ni/Au ohmic contact to unintentional doped GaN were investigated . The samples were annealed in a N2-ambient rapid thermal annealing furnace at 450, 550, 700, 800 and 900℃ for 1 min, respectively. It is found that ohmic contact begins to form after 700℃ anneals and, with the annealing temperature increasing,the contact resistance reduces continuously and the specific contact resistance values drops to their minimum levels of 6.6106O·cm2 at 900℃. The experimental analyses show that the low ohmic contact resistance requires Al-Ti solid-phase reaction sufficiently and the penetration of Al through Ti layer to reach GaN surface and , in the Meanwhile, N outdiffusing from GaN surface reacts with Ti to form TiN and creates N vacancies in GaN which act as donors increasing thereby the doping level at the metal-semiconductor interface, which makes electrons can tunnel easily to form low ohmic contact resistance.