Ohmic Contact to P-Type GaN

Abstract

Investigations of the new metal scheme for ohmic contact to p-GaN have been carried out. The specific contact resistance was measured to be ρc=3.6×10-3 Ω cm2 which is the lowest value ever reported for moderately doped p-GaN (4.4×1017/cm3). All metals were deposited on metalorganic chemical vapour deposition (MOCVD) grown p-GaN. The interaction mechanism between Ni and p-GaN has been investigated. Zn diffusion has been observed during annealing in Au–Zn/Ni on p-GaN. The interfacial reaction mechanism during annealing has been studied by secondary ion mass spectroscopy (SIMS) measurement. From this measurement, it is observed that Ni dissociates at the p-GaN surface and this dissociation promotes the Zn diffusion upon heat treatment. The electrical properties were studied using current–voltage (I–V) measurements at room temperature. The microstructure between the Ni and p-GaN interface was investigated using high-resolution transmission electron microscopy (TEM) before and after the heat treatment.

Low-resistance and transparent ohmic contacts to p-type GaN using Zn–Ni solid solution/Au scheme

“…The shift of the surface Fermi level could be associated with the formation of interfacial gallide phase, causing deep acceptor-like Ga vacancies to be generated near the GaN surface. 6 Furthermore, the in-diffusion of Zn into GaN might also contribute to the increase of carrier concentration, as suggested by Youn et al 17 However, further investigation is required to confirm this point. Second, this could be related to the formation of p-type Ni oxide, as noted from the Ni 2p core level behaviors ͑not shown͒.…”

“…16 Recently, in an effort to increase carrier concentration near the surface region of p-GaN, group II elements, such as Zn and Be, were intentionally added to a Au layer in direct contact to p-GaN. 17,18 It was shown that such schemes could be effective in increasing carrier concentration near the surface region. Very recently, expecting a similar doping effect, Song, Leem, and Seong 19 employed Ni-Mg solid solution to obtain low resistivity ohmic contacts to p-GaN.…”

Ohmic Contacts to P–GaN Based on the Single–Walled Carbon Nanotubes

“…Numerous papers have dealt with improving the ohmic properties of the contacts to p-GaN by increasing the charge carrier concentration in the surface region of pGaN by means of group II dopants incorporated into the metallization layer [2][3][4][5][6][7]. In the case of light emitting devices (diodes, lasers), when the ohmic contacts have to be also sufficiently transparent for visible light, this requirement has been satisfied by using very thin metallic contact layers on p-GaN.…”

Ohmic Contacts to p-GaN Using Au/Ni-Zn-O Metallization

“…Numerous procedures have been used to improve the ohmic properties of the contacts to p-GaN by increasing the charge carrier concentration in the surface region of p-GaN by means of group II dopants incorporated into the metallization layer [3][4][5][6][7][8]. For improving the optical transparency of the contacts, metallization structures based on ZnO have been used.…”