Calculations of the Specific Resistance of Contacts to III-V Nitride Compounds

ABSTRACTWe present calculations of the specific contact resistance for metals to GaN. Our calculations include a correct determination of the Fermi level taking into account the effect of the degenerate doping levels, required in creating tunneling ohmic contacts. Using a recently reported improved WKB approximation suitable in representing the depletion width at the metal-semiconductor interface, and a two band k-p model for the effective masses, specific contact resistance was determined as a function of doping concentration. The specific contact resistance was calculated using the best data available for barrier heights, effective masses and dielectric coefficients for GaN. Because the barrier height at the metal-semiconductor interface has a very large effect on the contact resistance and the available data is sketchy or uncertain, the effect of varying the barrier height on the calculated specific contact resistance was investigated. Further, since the III-V nitrides are being considered for high temperature device applications, the specific contact resistance was also determined as a function of temperature.

Download Full-text

Low-resistance Ohmic Contacts to N-face p-GaN for the Fabrication of Functional Devices

MRS Proceedings ◽

10.1557/proc-1202-i05-16 ◽

2009 ◽

Vol 1202 ◽

Author(s):

Seung-Cheol Han ◽

Jae-Kwan Kim ◽

jun Young Kim ◽

Joon Seop Kwak ◽

Kangho Kim ◽

...

Keyword(s):

Contact Resistance ◽

Oxide Layer ◽

Ohmic Contacts ◽

Specific Contact Resistance ◽

Surface Oxide Layer ◽

Band Bending ◽

Barrier Heights ◽

Bending Effect ◽

Treated Sample ◽

Specific Contact

AbstractThe electrical properties of Ni-based ohmic contacts N-face p-type GaN are presented. The specific contact resistance of N-face p-GaN exhibits a liner decrease from 1.01 × cm2 to 9.05 × 10-3 Ω cm2 for the as-deposited and the annealed Ni/Au contacts, respectively, with increasing annealing temperature Furthermore, the specific contact resistance could be decreased by four orders of magnitude to 1.03 × 10-4 Ω cm2 as a result of surface treatment using an alcohol-based (NH4)2S solution. The depth profile data measured by the intensity of O1s core peak in the x-ray photoemission spectra showed that the alcohol-based (NH4)2S treatment was effective in removing of the surface oxide layer of GaN. In addition, a Ga 2p core-level peak showed a red-shift of binding energy by 0.3 eV by alcohol-based (NH4)2S treatment, indicating that the surface Fermi level was shifted toward the valence-band edge. Thus, the low ohmic contact behavior observed in our treated sample might be explained in terms of the removal of the oxide layer and reducing the barrier heights by reduced band-bending effect.

Download Full-text

Ohmic Contacts to P-Type Epitexial and Imlanted 4H-SiC

Materials Science Forum ◽

10.4028/www.scientific.net/msf.527-529.895 ◽

2006 ◽

Vol 527-529 ◽

pp. 895-898 ◽

Cited By ~ 2

Author(s):

John Crofton ◽

John R. Williams ◽

A.V. Adedeji ◽

James D. Scofield ◽

S. Dhar ◽

...

Keyword(s):

Elevated Temperature ◽

Contact Resistance ◽

Barrier Height ◽

Ohmic Contacts ◽

Doping Concentration ◽

Theoretical Calculations ◽

Specific Contact Resistance ◽

Acceptor Doping ◽

Specific Contact ◽

P Type

Nickel ohmic contacts to p-type epitaxial and heavily implanted 4H-SiC are described. Room and elevated temperature results are presented. Elevated temperature measurements of specific contact resistance are compared to theoretical calculations. The calculations require the acceptor doping concentration and the contact’s barrier height. Epitaxial material has a known acceptor value thereby allowing the barrier height to be deduced by requiring agreement between the calculated and measured values of the contact resistance. Calculations of the contact resistance for implanted material use the barrier height from the epitaxial results along with a variable activated acceptor doping concentration which is adjusted to give agreement with measured room temperature specific contact resistances. Specific contact resistances as low as 7x10-6 ohm-cm2 fabricated on the Si face have been obtained to epitaxial 4H p-type material whereas contacts to implanted material result in much larger contact resistance values of 4x10-5 ohm-cm2. These results, when compared to theoretical calculations, indicate that activated acceptor doping concentrations in heavily implanted material are on the order of 2% of the implant concentration.

Download Full-text

Electrical Modelling and Characterisation of Alloyed Ohmic Contacts

MRS Proceedings ◽

10.1557/proc-318-153 ◽

1993 ◽

Vol 318 ◽

Cited By ~ 3

Author(s):

Geoffrey K. Reeves ◽

Patrick W. Leech ◽

H. Barry Harrison

Keyword(s):

Contact Resistance ◽

Transmission Line ◽

Ohmic Contact ◽

Ohmic Contacts ◽

Realistic Model ◽

Specific Contact Resistance ◽

Transmission Line Model ◽

Semiconductor Interface ◽

Line Model ◽

Specific Contact

ABSTRACTThis paper briefly reviews the standard Transmission Line Model (TLM) commonly used to measure the specific contact resistance of a planar ohmic contact. It is proposed that in the case of a typical Au-Ge-Ni alloyed ohmic contact, a more realistic model would need to take into account the presence of the alloyed layer at the metal-semiconductor interface. An alternative is described which is based on three contact layers and the two interfaces between them, thus forming a Tri-Layer Transmission Line Model (TLTLM). Expressions are given for the contact resistance Rc and the contact end resistance Re of this structure, together with a current division factor, f. Values for the parameters of this model are inferred from experimentally reported values of Rc and Re for two types of contact.

Download Full-text

Metal/Semiconductor Barrier Properties of Non-Recessed Ti/Al/Ti and Ta/Al/Ta Ohmic Contacts on AlGaN/GaN Heterostructures

Energies ◽

10.3390/en12142655 ◽

2019 ◽

Vol 12 (14) ◽

pp. 2655 ◽

Cited By ~ 3

Author(s):

Spera ◽

Greco ◽

Nigro ◽

Scalese ◽

Bongiorno ◽

...

Keyword(s):

Contact Resistance ◽

Barrier Height ◽

Ohmic Contacts ◽

Barrier Properties ◽

Specific Contact Resistance ◽

Conductive Atomic Force Microscopy ◽

Force Microscopy ◽

Ohmic Behavior ◽

Specific Contact ◽

Thermionic Field Emission

This paper compares the metal/semiconductor barrier height properties of non-recessed Ti/Al/Ti and Ta/Al/Ta contacts on AlGaN/GaN heterostructures. Both contacts exhibited a rectifying behavior after deposition and after annealing at temperatures up to 550 °C. The ohmic behavior was reached after annealing at 600 °C. High-resolution morphological and electrical mapping by conductive atomic force microscopy showed a flat surface for both contacts, with the presence of isolated hillocks, which had no significant impact on the contact resistance. Structural analyses indicated the formation of the Al3Ti and Al3Ta phases upon annealing. Furthermore, a thin interfacial TiN layer was observed in the Ti/Al/Ti samples, which is likely responsible for a lower barrier and a better specific contact resistance (c = 1.6 10−4 Ωcm2) with respect to the Ta/Al/Ta samples (c = 4.0 10−4 Ωcm2). The temperature dependence of the specific contact resistance was described by a thermionic field emission mechanism, determining barrier height values in the range of 0.58–0.63 eV. These results were discussed in terms of the different microstructures of the interfaces in the two systems.

Download Full-text

Improvement of the Specific Contact Resistance on P-Type 4H-SiC by Using a Highly P-Typed Doped 4H-SiC Layer Selectively Grown by VLS Transport

Materials Science Forum ◽

10.4028/www.scientific.net/msf.806.57 ◽

2014 ◽

Vol 806 ◽

pp. 57-60

Author(s):

Nicolas Thierry-Jebali ◽

Arthur Vo-Ha ◽

Davy Carole ◽

Mihai Lazar ◽

Gabriel Ferro ◽

...

Keyword(s):

Contact Resistance ◽

Ohmic Contacts ◽

Schottky Barrier Height ◽

Annealing Temperature ◽

Process Condition ◽

Specific Contact Resistance ◽

High Doping Level ◽

Annealing Temperatures ◽

Specific Contact ◽

P Type

This work reports on the improvement of ohmic contacts made on heavily p-type doped 4H-SiC epitaxial layer selectively grown by Vapor-Liquid-Solid (VLS) transport. Even before any annealing process, the contact is ohmic. This behavior can be explained by the high doping level of the VLS layer (Al concentration > 1020 cm-3) as characterized by SIMS profiling. Upon variation of annealing temperatures, a minimum value of the Specific Contact Resistance (SCR) down to 1.3x10-6 Ω.cm2 has been obtained for both 500 °C and 800 °C annealing temperature. However, a large variation of the SCR was observed for a same process condition. This variation is mainly attributed to a variation of the Schottky Barrier Height.

Download Full-text

Current Transport in Ti/Al/Ni/Au Ohmic Contacts to GaN and AlGaN

Materials Science Forum ◽

10.4028/www.scientific.net/msf.556-557.1027 ◽

2007 ◽

Vol 556-557 ◽

pp. 1027-1030 ◽

Cited By ~ 2

Author(s):

Ferdinando Iucolano ◽

Fabrizio Roccaforte ◽

Filippo Giannazzo ◽

A. Alberti ◽

Vito Raineri

Keyword(s):

Contact Resistance ◽

Field Emission ◽

Ohmic Contacts ◽

Theoretical Models ◽

Specific Contact Resistance ◽

Strong Increase ◽

Current Transport ◽

Electrical Characteristics ◽

Structural And Electrical Properties ◽

Specific Contact

In this work, the structural and electrical properties of Ti/Al/Ni/Au contacts on n-type Gallium Nitride were studied. An ohmic behaviour was observed after annealing above 700°C. The structural analysis showed the formation of an interfacial TiN layer and different phases in the reacted layer (AlNi, AlAu4, Al2Au) upon annealing. The temperature dependence of the specific contact resistance demonstrated that the current transport occurs through thermoionic field emission in the contacts annealed at 600°C, and field emission after annealing at higher temperatures. By fitting the data with theoretical models, a reduction of the Schottky barrier from 1.21eV after annealing at 600°C to 0.81eV at 800°C was demonstrated, together with a strong increase of the carrier concentration at the interface. The reduction of the contact resistance upon annealing was discussed by correlating the structural and electrical characteristics of the contacts.

Download Full-text

Modelling Geometrical Effects of Parasitic and Contact Resistance of FET Devices

MRS Proceedings ◽

10.1557/proc-427-147 ◽

1996 ◽

Vol 427 ◽

Cited By ~ 1

Author(s):

Geoffrey K. Reeves ◽

H. Barry Harrison ◽

Patrick W. Leech

Keyword(s):

Contact Resistance ◽

Material Properties ◽

Ohmic Contacts ◽

Difficult Problem ◽

Specific Contact Resistance ◽

Metal Silicide ◽

Transmission Line Model ◽

Specific Contact ◽

Geometrical Effects ◽

Contact Parameters

AbstractThe continual trend in decreasing the dimensions of semiconductor devices results in a number of technological problems. One of the more significant of these is the increase in contact resistance, Rc. In order to understand and counteract this increase, Rc needs to be quantitatively modelled as a function of the geometrical and material properties of the contact. However the use of multiple semiconductor layers for ohmic contacts makes the modelling and calculation of Rc a more difficult problem. In this paper, a Tri-Layer Transmission Line Model (TLTLM) is used to analyse a MOSFET ohmic contact and gatedrain region. A quantitative assessment of the influence on Rc of important contact parameters such as the metal-silicide specific contact resistance, the silicide-silicon specific contact resistance and the gate-drain length can thus be made. The paper further describes some of the problems that may be encountered in defining Rc when the dimensions of certain types of contact found in planar devices decrease.

Download Full-text

Ohmic Contacts to p-Type InGaAs/InP with a Graded Bandgap Heterobarrier

MRS Proceedings ◽

10.1557/proc-318-183 ◽

1993 ◽

Vol 318 ◽

Cited By ~ 5

Author(s):

Patrick W. Leech ◽

Geoffrey K. Reeves

Keyword(s):

Contact Resistance ◽

Ohmic Contacts ◽

Rutherford Backscattering Spectrometry ◽

Specific Contact Resistance ◽

Superlattice Structure ◽

Specific Contact ◽

P Type ◽

Metal Layers ◽

Anneal Temperature ◽

Graded Bandgap

ABSTRACTOhmic contacts to p-type InP with an In0.47Ga0.53As buffer layer and an interposed superlattice of 50 Å In0.47Ga0.53As/ 50 Å InP have been investigated. Initial studies of contacts to In0.47Ga0.53As/ InP without the superlattice structure have shown that Pd/Zn/Pd/Au metallization produced a lower specific contact resistance (pc = 1.1 × 10−4 Ω cm2) than Pd/Ge/Au, and over a wider range of anneal temperature than Au/Zn/Au. The incorporation of the superlattice in the p-In0.47Ga0.53As/ InP structure resulted in Pd/Zn/Pd/Au contacts with pc of 3.2 × 10−5 Ω cm2 as-deposited and 7.5 × 10−6 Ω.cm2 after a 500 °C anneal. The presence of Pd/Zn in the metallization was shown as important in reducing pc. Significant intermixing of the metal layers and In0.47Ga0.53As occured at ≥ 350 °C, as revealed by Rutherford backscattering spectrometry.

Download Full-text

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.924.385 ◽

2018 ◽

Vol 924 ◽

pp. 385-388 ◽

Cited By ~ 4

Author(s):

Roberta Nipoti ◽

Maurizio Puzzanghera ◽

Maria Concetta Canino ◽

Giovanna Sozzi ◽

Paolo Fedeli

Keyword(s):

Form Factor ◽

Contact Resistance ◽

Contact Area ◽

Room Temperature ◽

Ohmic Contacts ◽

Specific Resistance ◽

Thickness Ratio ◽

Specific Contact Resistance ◽

Specific Contact ◽

P Type

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 10-4Ωcm2at room temperature on p-type 4H-SiC with resistivity in the range 0.1 – 1 Ωcm.

Download Full-text