Journal of the Institute of Electronics Engineers of Korea SD (대한전자공학회논문지SD)

The Institute of Electronics and Information Engineers (대한전자공학회)
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A Study of Electrical Anisotropy of n-type a-plane GaN films grown on $\gamma$-plane Sapphire Substrates

$\gamma$-plane 사파이어 기판 위에 성장한 무분극 ${alpha}$-plane GaN 층의 전기적 비등방성 연구

  • Kim, Jae-Bum (School of Electronics and Electrical Engineering, Korea University) ;
  • Kim, Dong-Ho (School of Electronics and Electrical Engineering, Korea University) ;
  • Hwang, Sung-Min (School of Electronics and Electrical Engineering, Korea University) ;
  • Kim, Tae-Geun (Korea Electronics Technology Institute)
  • 김재범 (고려대학교 전자전기전파공학부) ;
  • 김동호 (고려대학교 전자전기전파공학부) ;
  • 황성민 (고려대학교 전자전기전파공학부) ;
  • 김태근 (고려대학교 전자부품연구원)
  • Received : 2010.03.22
  • Accepted : 2010.07.01
  • Published : 2010.08.25
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Abstract

We report on the electrical properties of Ti/Al/Ni/Au (20 nm/ 150 nm/ 30 nm/ 100 nm) Ohmic contacts and the anisotropic conductivity of n-type ${\alpha}$-plane ([11-20]) GaN grown on $\gamma$-plane ([1-102]) sapphire substrates. The Ti/Al/Ni/Au Ohmic contacts and their sheet resistances are characterized by using the transfer length method (TLM) as a function of azimuthal angles. It is found that the specific contact resistance does not depend on the axis orientation and there are significant electrical anisotropy in ${\alpha}$-plane GaN films on $\gamma$-plane sapphire substrates, and the sheet resistance varies with azimuthal angles. The sheet resistance values in the direction parallel to m-axis [1-100] are 25% ~ 75% lower than those parallel to c-axis [0001] directions. Thus, Basal stacking faults (BSFs) are offered as a feasible source of the anisotropic mobility in defected m-axis direction because the band-edge discontinuities owing to the differential band gap structure.

본 논문에서는 무분극 GaN층에서 관찰되는 성장축의 방향성에 따른 전기적 비등방성에 대한 연구를 수행하였다. 본 연구를 위해 $\gamma$-plane 사파이어 기판 상에 유기화학기상증착법 (Metal-organic chemical vapor deposition)을 이용하여 600 nm 두께의 ${\alpha}$-plane n-type GaN층을 성장시킨 후, Ti/Al/Ni/Au (20 nm/ 150 nm/ 30 nm/ 100 nm) 오믹 전극을 증착하여 transfer length method (TLM)로 접촉저항을 측정하였다. 그 결과, ${\alpha}$-plane GaN층이 갖는 축의 방향성에 의한 접촉저항이 차이는 없는 것을 확인하였고, 면저항 측정 시에는 m-축 방향에 비해 c-축 방향에서 발생하는 면저항 값이 약 25%~75% 정도 크게 발생하는 것을 확인할 수 있었다. 이러한 전기적 특성의 비등방성은 c-축 성장방향에 대해 수직방향을 갖는 기저적층결함 (basal stacking faults)의 생성으로 인한 전자들의 거동 저하에 의한 것으로 사료된다.

Keywords

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