Microstructure and Temperature Dependent Electrical Characteristics of Ohmic Contacts to AlGaN/GaN Heterostructures

2015 ◽  
Vol 821-823 ◽  
pp. 999-1002
Author(s):  
Giuseppe Greco ◽  
Ferdinando Iucolano ◽  
Fabrizio Roccaforte
Keyword(s):  
Ohmic Contacts ◽  
Microstructural Analysis ◽  
Specific Contact Resistance ◽  
Interfacial Region ◽  
Temperature Dependent ◽  
Scientific Debate ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
High Frequency Devices ◽  
Dimensional Electron Gas

AlGaN/GaN heterostructures are important materials for the fabrication of high power and high frequency devices. However, the mechanisms of Ohmic contacts formation on these systems are continuously under scientific debate. In this paper, a structural and electrical investigation of Ti/Al/Ni/Au Ohmic contacts to AlGaN/GaN heterostructures is reported. In particular, the behavior of Ti/Al/Ni/Au multilayers was monitored at different annealing temperatures. The contacts became Ohmic after annealing at 750°C and showed a decreasing temperature behavior of the specific contact resistanceRC, described by a thermionic field emission mechanism. On the other hand, annealing at 850°C led to a further reduction ofRC, with a slightly increasing dependence ofRCon the measurement temperature (here regarded as a “metal-like” behavior). The microstructural analysis of the interfacial region allowed to explain the results with the formation of metallic intrusions contacting directly the two dimensional electron gas.

Current Transport Mechanisms in Au-Free Metallizations for CMOS Compatible GaN HEMT Technology

2020 ◽  
Vol 1004 ◽  
pp. 725-730
Author(s):  
Fabrizio Roccaforte ◽  
Monia Spera ◽  
Salvatore Di Franco ◽  
Raffaella Lo Nigro ◽  
Patrick Fiorenza ◽  
...  
Keyword(s):  
Barrier Height ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Current Transport ◽  
Large Area ◽  
Si Substrates ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
Thermionic Field Emission

Gallium nitride (GaN) and its AlGaN/GaN heterostructures grown on large area Si substrates are promising systems to fabricate power devices inside the existing Si CMOS lines. For this purpose, however, Au-free metallizations are required to avoid cross contaminations. In this paper, the mechanisms of current transport in Au-free metallization on AlGaN/GaN heterostructures are studied, with a focus on non-recessed Ti/Al/Ti Ohmic contacts. In particular, an Ohmic behavior of Ti/Al/Ti stacks was observed after an annealing at moderate temperature (600°C). The values of the specific contact resistance ρc decreased from 1.6×104 Ω.cm2 to 7×105 Ω.cm2 with increasing the annealing time from 60 to 180s. The temperature dependence of ρc indicated that the current flow is ruled by a thermionic field emission (TFE) mechanism, with barrier height values of 0.58 eV and 0.52 eV, respectively. Finally, preliminary results on the forward and reverse bias characterization of Au-free tungsten carbide (WC) Schottky contacts are presented. This contact exhibited a barrier height value of 0.82 eV.

High Quality Non-Alloyed Pt Ohmic Contacts to P-Type GaN Using Two-Step Surface Treatment

1999 ◽  
Vol 595 ◽  
Author(s):  
Ja-Soon Jang ◽  
Seong-Ju Park ◽  
Tae-Yeon Seong
Keyword(s):  
Surface Treatment ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Transport Mechanisms ◽  
High Quality ◽  
Ammonium Sulfide ◽  
Current Voltage ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
P Type

AbstractTwo-step surface-treatment is introduced to obtain low resistance Pt contacts to ptype GaN. The first step is performed after the mesa etching process using buffered oxide etch (BOE) and ammonium sulfide [(NH4)2Sx]. This is followed by the second step using BOE. The Pt contact, which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH4)2Sx (10 min), produces a specific contact resistance of 3.0 (±3.8)×10-5 Ωcm2. However, the contact, that was simply BOE-treated, yields 3.1 (±1.1)×10-2 Ωcm2. This indicates that the two-step surface treatment is promising technique for obtaining high quality ohmic contacts to p-GaN. Investigation of the electronic transport mechanisms using current-voltage-temperature (I-V-T) data indicates that thermionic field emission is dominant in the surface-treated Pt contacts.

The Effects of Thermal Processing on Interfacial Microstructure for Thin Multilayered Metal Ohmic Contacts to p+-AlGaAs

1995 ◽  
Vol 382 ◽  
Author(s):  
M.W. Cole ◽  
W.Y. Han ◽  
K.A. Jones
Keyword(s):  
Ohmic Contacts ◽  
Annealing Temperature ◽  
Chemical Diffusion ◽  
Interfacial Microstructure ◽  
Specific Contact Resistance ◽  
Interfacial Region ◽  
Electrical Measurements ◽  
Two Phase ◽  
Specific Contact ◽  
P Type

ABSTRACTInterfacial microstructure and phase composition of PtTiGePd ohmic contacts to heavily C doped AlGaAs were investigated as a function of annealing temperature. Results of the material analyses were used to explain the specific contact resistances measured for each thermal treatment. Evidence of interdiffusion and compound formation between AIGaAs and Pd was visible in a Ga rich Pd-Ga-As reaction zone prior to heat treatment. This phase is critical for the formation of Ga vacancies, which upon heating are occupied by in-diffusing Ge. As the annealing temperature was elevated, from 530 - 600°C, As began to out-diffuse. This As out-diffusion, which is critical to the formation of good p-type ohmic contacts, contributed to the creation and development of the two phase TiAs/Pd12Ga2Ge5 interfacial region overlying the AlGaAs substrate. In response to the enhanced As out-diffusion at 600°C, the interfacial region became laterally continuous, compositionally uniform, and the specific contact resistance achieved its minimum value. Athigher annealing temperatures, ∼650°C, the electrical measurements degraded in response to intensive chemical diffusion and development of a broad, non-uniform multi-phased interfacial region.

Comparison of Ni/Au, Pd/Au, and Cr/Au Metallizations for Ohmic Contacts to p-GaN

1996 ◽  
Vol 449 ◽  
Author(s):  
J. T. Trexler ◽  
S. J. Pearton ◽  
P. H. Holloway ◽  
M. G. Mier ◽  
K. R. Evans ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Ohmic Contacts ◽  
Thermionic Emission ◽  
Specific Contact Resistance ◽  
Capping Layer ◽  
Dominant Conduction Mechanism ◽  
Current Voltage ◽  
Structural And Electronic Properties ◽  
Specific Contact ◽  
Thermionic Field Emission

ABSTRACTReactions between electron beam evaporated thin films of Ni/Au, Pd/Au, and Cr/Au on p-GaN with a carrier concentration of 9.8 × 1016 cm−3 were investigated in terms of their structural and electronic properties both as-deposited and following heat treatments up to 600°C (furnace anneals) and 900°C (RTA) in a flowing N2 ambient. Auger electron spectroscopy (AES) depth profiles were used to study the interfacial reactions between the contact metals and the p-GaN. The electrical properties were studied using room temperature current-voltage (1-V) measurements and the predominant conduction mechanisms in each contact scheme were determined from temperature dependent I-V measurements. The metallization schemes consisted of a 500 Å interfacial layer of Ni, Pd, or Cr followed by a 1000 Å capping layer of Au. All schemes were shown to be rectifying as-deposited with increased ohmic character upon heat treatment. The Cr/Au contacts became ohmic upon heating to 900°C for 15 seconds while the other schemes remained rectifying with lower breakdown voltages following heat treatment. The specific contact resistance of the Cr/Au contact was measured to be 4.3×10−1 Ωcm2. Both Ni and Cr have been shown to react with the underlying GaN above 400 °C while no evidence of a Pd:GaN reaction was seen. Pd forms a solid solution with the Au capping layer while both Ni and Cr tend to diffuse through the capping layer to the surface. All contacts were shown to have a combination of thermionic emission and thermionic field emission as their dominant conduction mechanism, depending on the magnitude of the applied reverse bias.

Impact of Surface Morphology on the Electrical Properties of Al/Ti Ohmic Contacts on Al-Implanted 4H-SiC

2011 ◽  
Vol 679-680 ◽  
pp. 413-416
Author(s):  
Alessia Frazzetto ◽  
Fabrizio Roccaforte ◽  
Filippo Giannazzo ◽  
Raffaella Lo Nigro ◽  
Corrado Bongiorno ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Electrical Properties ◽  
Surface Morphology ◽  
Ohmic Contacts ◽  
Metal Layer ◽  
Morphological Data ◽  
Specific Contact Resistance ◽  
Interfacial Region ◽  
Specific Contact ◽  
The Impact

This paper reports on the impact of the surface morphology on the properties of Ti/Al Ohmic contacts fabricated on Al-implanted 4H-SiC. In particular, the surface roughness of the Al-implanted regions after annealing at 1700 °C was strongly reduced by the using a protective carbon capping layer during annealing (the surface roughness decreased from 9.0 nm to 1.3 nm). In this way, also the morphology and the specific contact resistance of Ti/Al Ohmic contacts formed on the implanted regions could be improved. The electrical and morphological data were correlated with the structural properties of the reacted metal layer and of the metal/SiC interfacial region.

scholarly journals High Quality Non-Alloyed Pt Ohmic Contacts to P-Type GaN Using Two-Step Surface Treatment

2000 ◽  
Vol 5 (S1) ◽  
pp. 521-527
Author(s):  
Ja-Soon Jang ◽  
Seong-Ju Park ◽  
Tae-Yeon Seong
Keyword(s):  
Surface Treatment ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Transport Mechanisms ◽  
High Quality ◽  
Ammonium Sulfide ◽  
Current Voltage ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
P Type

Two-step surface-treatment is introduced to obtain low resistance Pt contacts to p-type GaN. The first step is performed after the mesa etching process using buffered oxide etch (BOE) and ammonium sulfide [(NH4)2Sx]. This is followed by the second step using BOE. The Pt contact, which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH4)2Sx (10 min), produces a specific contact resistance of 3.0 (±3.8)×10−5 Ωcm2. However, the contact, that was simply BOE-treated, yields 3.1 (±1.1)×10−2 Ωcm2. This indicates that the two-step surface treatment is promising technique for obtaining high quality ohmic contacts to p-GaN. Investigation of the electronic transport mechanisms using current-voltage-temperature (I-V-T) data indicates that thermionic field emission is dominant in the surface-treated Pt contacts.

scholarly journals Ohmic Contacts on p-Type Al-Implanted 4H-SiC Layers after Different Post-Implantation Annealings

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3468 ◽  
Author(s):  
Monia Spera ◽  
Giuseppe Greco ◽  
Domenico Corso ◽  
Salvatore Di Franco ◽  
Andrea Severino ◽  
...  
Keyword(s):  
Ohmic Contacts ◽  
Device Fabrication ◽  
Electrical Activation ◽  
Specific Contact Resistance ◽  
Emission Model ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
P Type ◽  
Post Implantation

This paper reports on the electrical activation and Ohmic contact properties on p-type Al-implanted silicon carbide (4H-SiC). In particular, the contacts were formed on 4H-SiC-implanted layers, subjected to three different post-implantation annealing processes, at 1675 °C, 1175 °C, and 1825 °C. Under these post-implantation annealing conditions, the electrical activation of the Al dopant species increased from 39% to 56%. The Ti/Al/Ni contacts showed an Ohmic behavior after annealing at 950 °C. The specific contact resistance ρc could be lowered by a factor of 2.6 with the increase of the post-implantation annealing temperature. The result can be useful for application in device fabrication. Moreover, the dependence of ρc on the active acceptor concentration followed the thermionic field emission model, with a barrier height of 0.63 eV.

Study of Ti/Al/Ni Ohmic Contacts to p-Type Implanted 4H-SiC

2018 ◽  
Vol 924 ◽  
pp. 377-380 ◽  
Author(s):  
Marilena Vivona ◽  
Giuseppe Greco ◽  
Corrado Bongiorno ◽  
Salvatore di Franco ◽  
Raffaella Lo Nigro ◽  
...  
Keyword(s):  
Ohmic Contacts ◽  
Annealing Temperature ◽  
Specific Contact Resistance ◽  
Electrical Characteristics ◽  
Key Factors ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
P Type ◽  
Resistance Value

This work reports on the electrical and microstructural properties of Ti/Al/Ni contacts to p-type implanted 4H-SiC obtained by rapid thermal annealing of a metal stack of Ti (70 nm)/Al (200 nm)/Ni (50 nm). The contact characteristics were monitored at increasing value of the annealing temperature. The Ohmic behavior of the contact, with a specific contact resistance value of 2.3×10-4Ω·cm2, is obtained for an annealing at 950 °C. The structural analyses of the contact, carried out by XRD and TEM, reveal the occurrence of reactions, with the detection of the Al3Ni2and AlTi phases in the upper part of the contact and of an epitaxially oriented TiC layer at the interface. These reactions are considered the key factors in the formation of an Ohmic contact in our annealed Ti/Al/Ni system. The temperature-dependence study of the electrical characteristics reveals a predominant thermionic field emission (TFE) mechanism for the current conduction through the contact, with a barrier height of 0.56 eV.

scholarly journals Thermally Stable Ohmic Contact to p-Type 4H-SiC Based on Ti3SiC2 Phase

2016 ◽  
Vol 858 ◽  
pp. 553-556 ◽  
Author(s):  
Tony Abi-Tannous ◽  
Maher Soueidan ◽  
Gabriel Ferro ◽  
Mihai Lazar ◽  
Christophe Raynaud ◽  
...  
Keyword(s):  
Thin Films ◽  
Electrical Properties ◽  
Magnetron Sputtering ◽  
Ohmic Contact ◽  
Room Temperature ◽  
Ohmic Contacts ◽  
Specific Contact Resistance ◽  
Specific Contact ◽  
Thermionic Field Emission ◽  
P Type

In this study, the electrical properties of Ti3SiC2 based ohmic contacts formed on p-type 4H-SiC(0001) 4°-off substrates were studied. The Ti3SiC2 thin films were grown by thermal annealing (from 900°C to 1200°C) of Ti50Al50 layer deposited by magnetron sputtering. XRD analyzes were performed on the samples to further investigate the compounds formed after annealing. Using TLM structures, the Specific Contact Resistance (SCR) at room temperature of all contacts was measured. The temperature dependence (up to 600°C) of the SCR was studied to understand the current mechanisms at the interface and to determine the barrier height value by fitting the experimental results using the thermionic field emission theory. Aging tests showed that Ti3SiC2 based contacts were stable up to 200h at 600°C under Ar.

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

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2655 ◽  
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.

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