Emerging trends in wide band gap semiconductors (SiC and GaN) technology for power devices

A critical review of theory and progress in Ohmic contacts to p-type SiC

The physics and technology of metal/semiconductor interfaces are key-points in the development of silicon carbide (SiC) based devices. Although in the last decade, the metal to 4HSiC contacts, either Ohmic or Schottky type, have been extensively investigated with important achievements, these remain even now an intriguing topic since metal contacts are fundamental bricks of all electronic devices. Hence, their comprehension is at the base of the improvement of the performances of simple devices and complex systems. In this context, this paper aims to highlight some relevant aspects related to metal/semiconductor contacts to SiC, both on n-type and p-type, with an emphasis on the role of the barrier and on the carrier transport mechanisms at the interfaces.

Metal/semiconductor contacts to silicon carbide: Physics and technology

This study shows that a thin Ni film on Al/Ti/4H-SiC metal pads allows to preserve the pad form factor during a 1000 °C/2 min treatment, provided that the Al and Ti film thicknesses are sufficiently thin. Moreover, by reducing the Al to Ti thickness ratio, droplet formation in the contact area is avoided and a mirror-like appearance is obtained. This optimal contact morphology corresponds to a specific contact resistance of few 10-4 Ωcm2 at room temperature on p-type 4H-SiC with resistivity in the range 0.1 – 1 Ωcm.

Ni-Al-Ti Ohmic Contacts with Preserved Form Factor and Few 10- 4 Ωcm2 Specific Resistance on 0.1-1 Ωcm p-Type 4H-SiC

The temperature dependent behaviour of a high power 4H-SiC PiN-diode was investigated by the adjustment of measured forward characteristics and quasistatic TCAD simulations in a temperature range from RT up to 773 K. The systematic analysis of the relevant physical parameters for the adjustment of measurements and simulations shows, that the predominating influence originates from the SRH (Shockley-Read-Hall) minority carrier lifetimes in the intrinsic region. The carrier lifetimes exhibit a negative temperature coefficient for temperatures above 673 K that disagrees with the theoretical models of the temperature dependence of the SRH recombination caused by just one effective type of impurity. The EH6/7 centers are the most promising candidates for additional recombination centers that become activated at higher temperatures and cause an increase in non-radiative carrier recombination that leads to decreasing SRH carrier lifetime.

Impact of the Activation of Carbon Vacancies at High Temperatures on the Minority Carrier Lifetimes in the Intrinsic Area of 4H-SiC PiN Rectifier

This study shows that an Al-Ti bilayer with an Al to Ti atomic ratio suitable for ohmic contacts on p-type 4H-SiC can be covered by a Ni film during the high temperature alloying process, without altering the ohmic nature, while eliminating a detrimental contact morphology caused by the presence of molten Al-Si during alloying. On 1×1020 cm−3 Al-implanted 4H-SiC layer, the RT specific contact resistance of this Ni-Al-Ti contact measured by TLM-C method is (3 ± 1)×10−6 Ωcm2.

R. A. Minamisawa

Papers

Ni-Al-Ti ohmic contacts on Al implanted 4H-SiC