High Temperature Stable Contacts for GaN HEMTs and LEDs

2008 ◽  
Vol 1108 ◽  
Author(s):  
S.J. Pearton ◽  
L.F. Voss ◽  
R. Khanna ◽  
Wantae Lim ◽  
L. Stafford ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Contact Resistance ◽  
Ohmic Contacts ◽  
Multiple Quantum Well ◽  
Drain Current ◽  
Specific Contact Resistance ◽  
Multiple Quantum ◽  
High Electron ◽  
Specific Contact

AbstractThere is continued interest in developing more stable contacts to a variety of GaN-based devices. In this paper we give two examples of devices that show improved thermal stability when boride, nitride or Ir diffusion barriers are employed in Ohmic contact stacks. AlGaN/GaN High Electron Mobility Transistors (HEMTs) were fabricated with Ti/Al/X /Ti/Au source/ drain Ohmic (where X is TiB2, ZrN, TiN, TaN or Ir) contacts and subjected to long-term annealing at 350°C. For GaN layers with an electron concentration of ∼3×1017 cm-3, the minimum specific contact resistance achieved is 6×10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800°C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. By comparison with companion devices with conventional Ti/Al/Ni/Au Ohmic contacts, the HEMTs with boride-based Ohmic metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350°C. The gate current for standard HEMTs increases during aging and the standard Ohmic contacts eventually fail by shorting to the gate contact. Similarly, InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni/Au/TiB2/Ti/Au or Ni/Au/Ir/Au p-Ohmic contacts. Both of these contacts showed superior long-term thermal stability compared to LEDs with conventional Ni/Au contacts.

TiW/TiWN/Pt Ohmic Contacts to n-Type 3C-SiC

2006 ◽  
Vol 911 ◽  
Author(s):  
Kirk Hofeling ◽  
Loren Rieth ◽  
Florian Solzbacher
Keyword(s):  
Contact Resistance ◽  
Room Temperature ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Test Duration ◽  
Capping Layer ◽  
Interface Reactions ◽  
Transmission Line Method ◽  
Specific Contact

AbstractTiW(40 nm)/TiWN(80 nm)/Pt(500nm) was investigated as a new high-temperature compatible contact stack to 3C-SiC for harsh environment applications. Performance of TiW/TiWN/Pt contacts deposited on unintentionally doped (8.85×1018 cm-3) 3C-SiC grown by LPCVD to a thickness of ~1μm on (100) Si are reported. The linear transmission line method was used to determine specific contact resistance (ρc) at room temperature and for long-term tests at 300 °C. As deposited contacts were Ohmic with a ρc range of 1×10-4 to 1×10-3 cm2. These contacts were annealed for five minutes in forming gas (8% H2 92% Ar), at temperatures from 450 to 950 °C and all retained Ohmic character. Annealing samples at 450, 550 and 950 °C decreased ρc while anneling between 650 and 850 °C generally increased ρc.Auger Electron Spectroscopy (AES) analysis was performed on a sample annealed at 750 °C. The as-received surface was composed of Si and O; after a brief sputter etch a characteristic Pt peak became visible and the O peak decreased substantially. Depth profiles detected Si throughout the Pt capping layer but not in the TiW layers. We suspect that Si diffuses from the SiC substrate into the Pt capping layer and surface Si also reacts with O2 to from an oxide. These reactions, in combination with incomplete SiC/TiW interface reactions, are suspected to cause the increase of ρc for samples annealed between 650 and 850 °C. Annealing at 950 °C gave the lowest contact resistance of 2.3×10-5. Long-term testing at 300 °C for 190 hours, in atmosphere, was performed on contacts annealed at 450 °C. When heated, the contacts initial ρc of 2.1×10-4 cm2 increased to ~4×10-3 cm2 which remained stable for the test duration. After long-term testing the sample ρc measured at room temperature decreased to 9.8×10-5 cm2.

Optimization of Pd/Zn/Pd/Au Ohmic Contacts to p-Type inGaAs/ InP

1994 ◽  
Vol 337 ◽  
Author(s):  
Patrick W Leech ◽  
Geoffrey K. Reeves
Keyword(s):  
Thermal Stability ◽  
Electrical Properties ◽  
Contact Resistance ◽  
Ohmic Contacts ◽  
Critical Thickness ◽  
Specific Contact Resistance ◽  
Zn Doping ◽  
Specific Contact ◽  
P Type ◽  
Thermal Stability Of

ABSTRACTThe electrical properties of Pd/Zn/Pd/Au based ohmic contacts to p-type In0 47Ga0 53As/ InP with an interposed superlattice of 50Å In047Gao 53As/ 50 Å InP have been investigated. In this study, several configurations of the Pd/Zn/Pd/Au metallization were fabricated with varying thicknesses of the Zn and interfacial Pd layers in the range 0 to 400 Å. The lowest values of specific contact resistance, ρc, were 1.2 x 10-5 Ω cm2 as-deposited and 7.5 x 106 Ω cm2 for samples annealed at 500 °C. In the as-deposited structures, ρc was reduced by an increase in thickness of both the Zn and Pd layers to 300 Å. For annealed samples, a critical thickness of the Zn ≥ 50 Å and Pd ≥ 100 Å layers was required in order to significantly reduce the magnitude of ρc. These results are consistent with a model of Pd/Zn contacts based on Zn doping of the interface. Studies of thermal stability of the contacts at 400 °C and 500 °C have shown that the Zn/Pd/Au and Pd/Zn/Pd/Au configurations were significanty lower in ρc at extended ageing times than the Pd/Au contacts.

scholarly journals Ti/Al Ohmic Contacts to n-Type GaN Nanowires

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Gangfeng Ye ◽  
Kelvin Shi ◽  
Robert Burke ◽  
Joan M. Redwing ◽  
Suzanne E. Mohney
Keyword(s):  
Thermal Stability ◽  
Contact Resistance ◽  
Cross Sections ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Transmission Line Model ◽  
Gan Nanowires ◽  
Transmission Electron ◽  
Titanium Aluminum ◽  
Specific Contact

Titanium/aluminum ohmic contacts to tapered n-type GaN nanowires with triangular cross-sections were studied. To extract the specific contact resistance, the commonly used transmission line model was adapted to the particular nanowire geometry. The most Al-rich composition of the contact provided a low specific contact resistance (mid10−8 Ωcm2) upon annealing at 600 °Cfor 15 s, but it exhibited poor thermal stability due to oxidation of excess elemental Al remaining after annealing, as revealed by transmission electron microscopy. On the other hand, less Al-rich contacts required higher annealing temperatures (850 or 900 °C) to reach a minimum specific contact resistance but exhibited better thermal stability. A spread in the specific contact resistance from contact to contact was tentatively attributed to the different facets that were contacted on the GaN nanowires with a triangular cross-section.

Titanium Tungsten (TiW) for Ohmic contacts to n-and p-type 4H-SiC

2000 ◽  
Vol 640 ◽  
Author(s):  
S.-K. Lee ◽  
C.-M. Zetterling ◽  
M. Östling
Keyword(s):  
High Temperature ◽  
Contact Resistance ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Term Stability ◽  
Long Term Stability ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
P Type

ABSTRACTIn the present work, we investigated sputtered titanium tungsten (TiW) contacts for Ohmic contacts to both n- and p-type 4H-SiC with long-term stability under high temperature (500°C).. Epitaxial layers with a doping concentration of 1.3×1019 and 6×1018 cm−3 were used. After high temperature annealing (>950°C) sputtered TiW contacts showed Ohmic behavior with good uniform distribution of the specific contact resistance. We obtained an average specific contact resistance (pc) of 4×10−5 Ωcm2 and 1.2 ∼ 1.7×10−4 Ωcm2 for p- and n-type, respectively from linear TLM measurement. We also found some variation of the specific contact resistance and the sheet resistance from our TLM measurement for p-type contacts. We will discuss this behavior with the measurement of SIMS. Long-term stability with a top-cap layer is also discussed

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

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.

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

2007 ◽  
Vol 556-557 ◽  
pp. 1027-1030 ◽  
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.

Modelling Geometrical Effects of Parasitic and Contact Resistance of FET Devices

1996 ◽  
Vol 427 ◽  
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.

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

1993 ◽  
Vol 318 ◽  
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.

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

2018 ◽  
Vol 924 ◽  
pp. 385-388 ◽  
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.

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