Metallization scheme for highly low-resistance, transparent, and thermally stable Ohmic contacts to p-GaN

Abstract

We report on a promising metallization scheme for high-quality Ohmic contacts to surface-treated p-GaN:Mg (2 -3ϫ10 17 cm Ϫ3 ). It is shown that the as-deposited Pt/Ru contact produces a specific contact resistance of 7.8(Ϯ2.2)ϫ10 Ϫ4 ⍀ cm 2 . However, annealing of the contact at 600°C for 2 min results in a resistance of 2.2(Ϯ2.0)ϫ10 Ϫ6 ⍀ cm 2 . It is also shown that the light transmittance of the annealed contact is 87.3% at 470 nm. Furthermore, the surface of the contact annealed at 600°C for 30 min is found to be very smooth with a rms roughness of 0.8 nm. These results strongly indicate that the Pt/Ru can be a suitable scheme for the fabrication of high-performance laser diodes or other devices.

Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

“…Other approaches aim at lowering the Schottky barrier height (SBH) by chemical passivation and removal of oxide layer on p-GaN [12][13][14]. More recently, promising approaches using Ni-based alloys such as Ni-La, Ni-Zn, Ni-Mg, and Ni-Cu produced very low specific contact resistivity in 10 −5 ∼10 −6 cm 2 range, depending on metal schemes [15][16][17][18].…”

Effects of Surface Treatment on the Electrical Properties of Ohmic Contacts to (In)GaN for High Performance Optical Devices

“…In fact, the high contact resistance of GaN is one of major obstacles to the realisation of long-lifetime operation of GaN-based optical devices. Thus, to develop high-quality Ohmic contacts, different surface treatments using KOH [2], HNO 3 : HCl [3], buffered oxide etch (BOE) [4,5], (NH 4 ) 2 S x [6], and Na 2 S [7] solutions have been employed. Kim et al [3] showed that for Pd/Au Ohmic contacts to p-GaN, the surface treatment with HNO 3 : HCl leads to a specific contact resistance of $10 --4 W cm 2 .…”

“…The low resistance was attributed to the effective removal of native oxide. Jang et al [4,5] showed that the two-step surface treatment with BOE is an effective process for the removal of native oxide and causes an increase in the carrier concentration at the surface region, resulting in a large reduction in the specific contact resistance. Huh et al [6] showed that the surface modification with alcohol-based (NH 4 ) 2 S x solutions is effective in improving the Ohmic contact behaviour.…”

Carrier Transport Mechanism of Pd/Pt/Au Ohmic Contacts to p-GaN in InGaN Laser Diode

“…However, because of difficulty in obtaining a hole concentration over 10 18 cm --3 and the absence of metals having a work function higher than that of p-GaN, achieving low resistance ohmic contacts to p-GaN has been particularly challenging. So far, many experiments on the electrical characteristics of metal contacts to p-GaN have been carried out, mainly focusing on the variation of metal scheme and surface treatments [2][3][4]. In order to achieve the low-resistance ohmic contacts to p-GaN, understanding of the carrier transport phenomena at the interface between metal and p-GaN is essential.…”