Ti/Al-based contacts to p-type SiC and GaN for power device applications

Abstract

Metal contacts (Schottky or Ohmic) to p-type wide band gap (WBG) semiconductors SiC and GaN are important for power devices technologies. This work reports on the properties of Ti/Al-based contacts to p-type 4H-SiC and p-type GaN, monitored using different techniques and test-patterns. In particular, in the case of p-type SiC, Ti/Al and Ti/Al/W contacts showed a superior Ohmic behavior after annealing at 900-1100 8C (with r c % 1.5-6 Â 10 À4 Vcm 2 ), attributed to the formation of Ti-and Al-containing phases at the interface and in the stack. Due to the lower r c with respect to Ni-based contacts, Ti/Al allowed a reduction of the forward voltage drop in 4H-SiC p-n junctions. On the other hand, in the case of p-type GaN, Ti/Al contacts exhibited a higher barrier height (2.08 eV) with respect to Ni contacts. Hence, they can be promising as Schottky gates in high electron mobility transistors (HEMTs). However, temperature-dependent electrical measurements revealed a decrease of the barrier height down to 1.60 eV upon annealing at 800 8C, with an increase of the leakage current in test-diodes. This result provided an important indication for the practical use of Ti/Al gate electrodes for the fabrication of normally off HEMTs with a p-GaN gate.

Mechanisms of Ohmic Contact Formation of Ti/Al-Based Metal Stacks on p-Doped 4H-SiC

“…Based on the Thermionic Field Emission (TFE) model [ 21 ], Equation (10) can be used to determine the Schottky barrier height , where describes the Boltzmann constant, the Planck constant, the effective tunneling mass (here 0.91 electron masses [ 22 , 23 , 24 ]), the vacuum permittivity and the relative permittivity of 4H-SiC (here 9.7 [ 4 , 22 , 23 ]). …”

“… ( a ) Normalized average specific contact resistance ( b ) Determined Schottky barrier heights form this work and literature. Ohmic contacts from literature fabricated on epitaxial regions are indicated with ∇ ([ 3 , 4 , 6 , 10 , 11 , 24 ]), ohmic contacts from literature fabricated on implanted regions are indicated with Δ ([ 22 , 23 , 26 , 27 ]). …”

Low Gate Lag Normally-Off p-GaN/AlGaN/GaN High Electron Mobility Transistor with Zirconium Gate Metal

“…of magnesium (Mg) doping GaN, or gate dielectric. Moreover, the Schottky barrier height can be increased by the metal work function, which contacts to p-GaN [11].…”

“…To further improve the performance of power device, breakdown voltage can be enhanced by the gate metal, concentration of magnesium (Mg) doping GaN, or gate dielectric. Moreover, the Schottky barrier height can be increased by the metal work function, which contacts to p-GaN [11].…”

Stable and reliable ohmic contact on p-type 4H-SiC up to 1500 h of aging at 600 °C

“…Another study reported the formation of contacts on highly p-type 4H-SiC after annealing at 800ºC (relatively low temperature) for 30 min, but such long annealing time can be detrimental for MOSFET fabrication process [19]. On the other hand, a great attention is given to Al-Ti alloy which has shown stable low SCRs on the order of 10 −3 -10 −5 Ω•cm 2 on p-type SiC [20,21]. The formation of the Mn+1AXn phase Ti3SiC2, after annealing of Al-Ti alloy at high temperature, is the reason behind the stability of the ohmic contact on p-type 4H-SiC [12,22,23].…”