Ohmic contacts to p-GaN Using Au/Ni-Mg-O Metallization

Abstract

Electrical characteristics and elemental depth profiles of ohmic contacts to p-GaN using Au/Ni-Mg-Ox metallization have been investigated. The objective was to examine the possibilities of increasing the charge carrier concentration in the surface region of GaN by adding Mg, thus of a p-type dopant into the Au/NiOx metallization structure. For this purpose, a Ni-Mg-Ox layer with a low concentration of Mg was deposited on p-GaN by dc reactive magnetron sputtering. The top Au layer was deposited in a similar way. The fabricated contact structures were annealed in N 2 . When the Ni-Mg layer in the Au/Ni-Mg-Ox/p-GaN structure was deposited in an atmosphere with a low concentration of oxygen (0.2 at%), the structure exhibited a low resistance ohmic nature.

Improving the ohmic properties of contacts to P–GaN by adding p–type dopants into the metallization layer

“…While studying the effect of the NiO x layer with a low concentration of oxygen upon the electrical properties of ohmic contacts Au/NiO x /p-GaN [10] it was found that a low-resistance ohmic contact was provided by Au/NiO x layers deposited by reactive magnetron sputtering and annealed not only in oxygen but also in nitrogen. Preliminary results have also shown that Ni-Mg-O and Ni-Zn-O layers with a low concentration of oxygen deposited on p-GaN by DC magnetron sputtering have, after annealing in nitrogen, an ohmic nature and in comparison with an identical metallization structure without addition of the group II element Mg or Zn they have a lower value of contact resistivity [11].…”

Research of Acceptor Impurity Thermal Activation in Gan : Mg Epitaxial Layers

“…При этом для эффективной ра-боты многих приборных структур необходимо получение высоких концентраций свободных носите-лей заряда в слоях p−GaN. Так, для формирования высококаче-ственного омического контакта необходимая концентрация дырок в приповерхностном слое должна быть не ниже 1 · 10 18 см −3 [3].…”

Mechanism of Ohmic Cr/Ni/Au contact formation on p-GaN

“…[1][2][3][4] One of the important steps in fabrication of such devices is the formation of lowresistivity Ohmic contacts both to n-GaN and p-GaN films. 7 Different types of p-contacts were proposed as monolayer, [8][9][10] bilayer, 7,10-12 or trilayer [12][13][14][15][16][17][18] metallization combining Au, Ni, Ti, Pt, Cr, Pd, etc., elements but usually with relatively high specific contact resistance. Such contacts prepared in optimized conditions can yield low specific contact resistance ranging between 10 À6 and 10 À8 X cm 2 .…”

“…Many studies of Ohmic contacts to n-GaN have shown that the best candidate is the Ti/Al/Ni/Au and Ti/Al/Pt/Au based metallization. 7,[11][12][13][14][15] Kalaitzakis et al 16 obtained Ohmic behavior with both Cr/Au and Ni/Au bilayer schemes but achieved a lower specific contact resistance (2.6 Â 10 À3 X cm 2 ) in as-deposited Cr/Au contact. 5,6 However, the formation of low-resistivity Ohmic contact to p-GaN seems to be so far nontrivial and still attracts much attention.…”