Very-low-specific-resistance Pd/Ag/Au/Ti/Au alloyed ohmic contact to p GaN for high-current devices

Abstract

We report on Pd/Ag/Au/Ti/Au alloyed metallic contact to p GaN. An 800 °C anneal for 1 min in flowing nitrogen ambient produces an excellent ohmic contact with a specific contact resistivity close to 1×10−6 Ω cm2 and with good stability under high current operation conditions. This high-temperature anneal forms an alloy between Ag, Au, and p GaN resulting in a highly p-doped region at the interface. Using x-ray photoelectron spectroscopy and x-ray diffraction analysis, we confirm that the contact formation mechanism is the metal intermixing and alloying with the semiconductor.

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

“…The AES and GXRD results showed that the increase in the annealing temperature above 600 • C leads to indiffusion of Pt, Pd, and Au atoms and formation of the Ga 3 Pt 5 , Ga 2 Pd 5 , and Au 7 Ga 2 phases at the metal/GaN in- terface. This is in good agreement with those previously reported by other groups [19][20][21][22][23][24][25][26][27][28][29]. It is well known that for the Pt-and Pd-based contacts for p-GaN, Pt and Pd readily react with GaN and form Pd-Ga and Pt-Ga related phases upon annealing [19][20][21][22][23][24][25][26][27][28][29].…”

“…The p-GaN layer was ultrasonically degreased with acetone, methanol, and methanol for 5 min in each step, and then rinsed with deionized water followed by N 2 blowing. The p-GaN layers were then boiled in a buffered hydrofluoric (BHF) solution for 10 min to remove surface oxide layers [29]. For the measurement of contact resistivity, an active region was defined by inductively-coupledplasma reactive ion etching (ICP-RIE) using a mixture of BCl 3 /Cl 2 /Ar gases.…”

“…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]. From those approaches, Ni/Au is although being used as p-contact electrode for conventional InGaN/GaN LEDs, various Pt-and Pd-based ohmic contact such as Pt/Ni/Au, Pt/Ru, Pt, Pt/Au, Ti/Pt/Au, Pd/Au, Pd/Ni, Pd/Pt/Au, Pt/Pd/Au, and Pd/Ag/Au/Ti/Au also have been investigated significantly due to the fact that those metals have large work functions and easily react with gallium during an annealing process [7,13,[19][20][21][22][23][24][25][26][27][28][29]. The specific contact resistivities of both the Pt-and Pd-based ohmic contacts are typically in the range of low 10 −3 ∼10 −5 cm 2 .…”

Ir-based diffusion barriers for Ohmic contacts to p-GaN

“…The surface morphology can become very rough, especially in the case of the common Ni/Au contact, and the contact can fail to display Ohmic properties. A number of approaches to compensate for this problem have been explored, including the use of non-alloyed Rh-based contacts [22] and Pd [23], W [29], as well as families of borides [30,31] and nitrides [32].…”

Thermal stability of Ni/Ag contacts on p‐type GaN

“…The development and fabrication of flip-chip GaN based LEDs has prompted the search for highreflectivity metallizations, in addition to stable, ohmic and low resistivity contact to GaN. There are few researchers who use silver (Ag) or metal/silver as metal contact to n-GaN, and it is rarely used as metal contacts to p-GaN [15], although silver has good electrical resistivity (1.59 × 10 -6 Ωcm) and thermal conductivity (1 cal/cm-s-°C) [16]. Moreover, silver can form electrically superior contacts to p-GaN than Ni/Au, and has higher reflectivity than Al [17].…”