Structure and Electrical Properties of Cu/Ge Ohmic Contacts

1995 ◽  
Vol 402 ◽  
Author(s):  
S. Oktyabrsky ◽  
M. O. Aboelfotoh ◽  
J. Narayan
Keyword(s):  
Ohmic Contacts ◽  
Contact Layer ◽  
Interfacial Microstructure ◽  
Contact Resistivity ◽  
Electrical Characteristics ◽  
Secondary Phases ◽  
Gaas Substrates ◽  
Wide Range ◽  
Specific Contact ◽  
Average Lattice

AbstractChemistry, crystal structure, interfacial microstructure and electrical characteristics of novel Cu-Ge alloyed ohmic contacts to n-type GaAs with a very low specific contact resistivity ((4–6)×10−7 Ω·cm2 for n∼1×1017 cm−3) were investigated by various methods. The Cu-Ge alloys with a wide range of Ge concentration, from 15 to 40 at %, were prepared by depositing sequentially Cu and Ge layers (or vise versa) onto GaAs substrates at room temperature followed by annealing at 400°C. It is shown that Cu reacts only with Ge to form the ξ and ε1-Cu3Ge phases. The latter has an orthorhombic structure with average lattice parameters: a = 5.301 Å, bo = 4.204 Å, co = 4.555 Å, arising from the parent hexagonal ξ-phase by Cu-Ge ordering along ao. The interface with GaAs is atomically sharp and free from secondary phases. The ε1-Cu3Ge ordered phase which is chemically inert with respect to GaAs, is believed to be responsible for high thermal stability (up to 450°C), interface sharpness, high contact layer uniformity and low specific resistivity of 6 μΩ cm. Formation of the Cu-Ge phases creates a highly doped n+-GaAs surface layer which leads to the low contact resistivity.

Electrical and microstructural characteristics of Ge/Cu ohmic contacts to n-type GaAs

1997 ◽  
Vol 12 (9) ◽  
pp. 2325-2331 ◽  
Author(s):  
M. O. Aboelfotoh ◽  
S. Oktyabrsky ◽  
J. Narayan ◽  
J. M. Woodall
Keyword(s):  
Ohmic Contacts ◽  
Field Effect Transistors ◽  
Contact Resistivity ◽  
Microstructural Characteristics ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Wide Range ◽  
Specific Contact ◽  
Abrupt Interface

It is shown that Cu–Ge alloys prepared by depositing sequentially Cu and Ge layers onto GaAs substrates at room temperature followed by annealing at 400 °C form a low-resistance ohmic contact to n-type GaAs over a wide range of Ge concentration that extends from 15 to 40 at. %. The contacts exhibit a specific contact resistivity of 7 × 10−7 Ω cm2 on n-type GaAs with doping concentrations of 1 × 1017 cm−3. The contact resistivity is unaffected by varying the Ge concentration in the range studied and is not influenced by the deposition sequence of the Cu and Ge layers. Cross-sectional high-resolution transmission electron microscopy results show that the addition of Ge to Cu in this concentration range causes Cu to react only with Ge forming the ξ and ε1–Cu3Ge phases which correlate with the low contact resistivity. The ξ and ε1–Cu3Ge phases have a planar and structurally abrupt interface with the GaAs substrate without any interfacial transition layer. It is suggested that Ge is incorporated into the GaAs as an n-type impurity creating a highly doped n+-GaAs surface layer which is responsible for the ohmic behavior. n-channel GaAs metal-semiconductor field-effect transistors using ohmic contacts formed with the ξ and ε1–Cu3Ge phases demonstrate a higher transconductance compared to devices with AuGeNi contacts.

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.

scholarly journals Ohmic contacts to Si-implanted and un-implanted n-type GaN

1995 ◽  
Vol 395 ◽  
Author(s):  
J. Brown ◽  
J Ramer ◽  
K. ZHeng ◽  
L.F. Lester ◽  
S.D. Hersee ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Ohmic Contacts ◽  
Annealing Temperature ◽  
Contact Resistivity ◽  
Contact Structures ◽  
Specific Contact Resistance ◽  
Resistance Variation ◽  
Specific Contact ◽  
Metal Layers ◽  
Nitrogen Vacancies

ABSTRACTWe report on ohmic contacts to Si-implanted and un-implanted n-type GaN on sapphire. A ring shaped contact design avoids the need to isolate the contact structures by additional implantation or etching. Metal layers of Al and Ti/Al were investigated. On un-implanted GaN, post metalization annealing was performed in an RTA for 30 seconds in N2 at temperatures of 700, 800, and 900°C, A minimum specific contact resistance (rc) of 1.4×10−5 Ω-cm2 was measured for Ti/Al at an annealing temperature of 800°C. Although these values are reasonably low, variations of 95% in specific contact resistance were measured within a 500 µm distance on the wafer. These results are most likely caused by the presence of compensating hydrogen. Specific contact resistance variation was reduced from 95% to 10% by annealing at 900°C prior to metalization. On Si-implanted GaN, un-annealed ohmic contacts were formed with Ti/Al metalization. The implant activation anneal of 1120°C generates nitrogen vacancies that leave the surface heavily n-type, which makes un-annealed ohmic contacts with low contact resistivity possible.

A Microstructual Analysis of Au/Pd/Ti Ohmic Contacts for GaAs-Based Heterojunction Bipolar Transistors (HJBTs)

1991 ◽  
Vol 240 ◽  
Author(s):  
Bernard M. Henry ◽  
A. E. Staton-Bevan ◽  
V. K. M. Sharma ◽  
M. A. Crouch ◽  
S. S. Gill
Keyword(s):  
Structural Properties ◽  
Heterojunction Bipolar Transistors ◽  
Ohmic Contacts ◽  
Heat Treatments ◽  
Bipolar Transistors ◽  
Contact Resistivity ◽  
Base Region ◽  
Specific Contact ◽  
Specific Contact Resistivity ◽  
Contact Resistivities

ABSTRACTAu/Pd/Ti and Au/Ti/Pd ohmic structures to thin p+-GaAs layers have been investigated for use as contacts to the base region of HJBTs. The Au/Pd/Ti contact system yielded specific contact resistivities at or above 2.8 × 10−5Ω:cm2. Heat treatments up to 8 minutes at 380°C caused only limited interaction between the metallization and the semiconductor. The metal penetrated to a maximum depth of ≃2nm. Specific contact resistivity values less than 10−5Ωcm2 were achieved using the Au/Ti/Pd (400/75/75nm) scheme. The nonalloyed Au/Ti/Pd contact showed the best combination of electrical and structural properties with a contact resistivity value of 9 × 10≃6Ωcm2 and Pd penetration of the GaAs epilayer to a depth of cs30nm.

Investigation of Cu-Ge/Gaas Metal-Semiconductor Interfaces for Low Resistance Ohmic Contacts

1996 ◽  
Vol 448 ◽  
Author(s):  
Serge Oktyabrsky ◽  
M.A. Borek ◽  
M.O. Aboelfotoh ◽  
J. Narayan
Keyword(s):  
Interfacial Layer ◽  
Ohmic Contacts ◽  
High Thermal Stability ◽  
Contact Resistivity ◽  
Polycrystalline Layer ◽  
Ohmic Behavior ◽  
Semiconductor Interfaces ◽  
Transmission Electron ◽  
Specific Contact ◽  
Specific Contact Resistivity

AbstractChemistry and interfacial reactions of the Cu-Ge alloyed ohmic contacts to n-GaAs with extremely low specific contact resistivity (6.5×10-7 Ω·cm2 for n~1017 cm-3) have been investigated by transmission electron microscopy, EDX and SIMS. Unique properties of the contact layers are related to the formation (at Ge concentration above 15 at.%) of a polycrystalline layer of ordered orthorhombic ε1-Cu3Ge phase. Formation of the ε1-phase is believed to be responsible for high thermal stability, interface sharpness and uniform chemical composition. The results suggest that the formation of the ζ- and ε1,-Cu3Ge phases creates a highly Ge-doped n+-GaAs interfacial layer which provides the low contact resistivity. Layers with Ge deficiency to form ζ-phase show nonuniform intermediate layer of hexagonal β-Cu3As phase which grows epitaxially on Ga{111} planes of GaAs. In this case, released Ga diffuses out and dissolves in the alloyed layer stabilizing the ζ-phase which is formed in the structures with average Ge concentration of as low as 5 at.%. These layers also exhibit ohmic behavior.

Improved Nickel Silicide Ohmic Contacts to N-Type 4H and 6H-SiC Using Nichrome

1996 ◽  
Vol 423 ◽  
Author(s):  
E. D. Luckowski ◽  
J. R. Williams ◽  
M. J. Bozack ◽  
T. Isaacs-Smith ◽  
J. Crofton
Keyword(s):  
Barrier Layer ◽  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Contact Layer ◽  
Weight Percent ◽  
Nickel Silicide ◽  
Electrical Characteristics ◽  
Success Rates ◽  
Diffusion Barrier Layer

AbstractResults are reported for ohmic contacts formed on n-type 4H and 6H-SiC using nichrome (80/20 weight percent Ni/Cr). In comparison to contacts formed on 6H-SiC using pure Ni, the electrical characteristics of these NiCr contacts are similar (∼ 1E-5 Ω-cm2 for moderately doped material), and composite Au/NiCr contacts exhibit good stability during long-term anneals (∼ 2500 hr) at 300 C without the requirement of a diffusion barrier layer between the ohmic contact layer and the Au cap layer. The use of NiCr also results in success rates near 100% for direct wire bonding to the Au cap layers.

Cr/Ni/Au ohmic contacts to the moderately doped p- and n-GaN

1996 ◽  
Vol 449 ◽  
Author(s):  
Taek Kim ◽  
Myung C. Yoo ◽  
Taeil Kim
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Ohmic Contacts ◽  
Metalorganic Chemical Vapor Deposition ◽  
Chemical Vapor ◽  
Contact Resistivity ◽  
Sapphire Substrates ◽  
Specific Contact ◽  
Specific Contact Resistivity ◽  
Metalorganic Chemical

ABSTRACTWe report new Cr/Ni/Au and Ni/Cr/Au tri-layer metallization schemes for achieving low resistance ohmic contacts to moderately doped p- (∼1 × 1017/cm3), and n-GaN (∼1 × 1018/cm3) respectively. The metallizations were thermally evaporated on 2 μm-thick GaN layers grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD). Comparisons with bi-layer metallizations such as Ni/Au and Cr/Au were also made. The Cr/Ni/Au contacts showed a low specific contact resistivity of 9.1 × 10−5 Ω⋅cm2 to n-GaN while that of Ni/Cr/Au to p-GaN was 8.3 × 10−2 Ω⋅cm2. The Ni/Cr/Au contacts also showed a low specific contact resistivity of 2.6 × 10−4 Ω⋅cm2 to n-GaN. The Ni/Cr/Au metallization could made reasonable ohmic contacts to p- and n-GaN simultaneously

Microstructure, electrical properties, and thermal stability of Au-based ohmic contacts to p-GaN

1997 ◽  
Vol 12 (9) ◽  
pp. 2249-2254 ◽  
Author(s):  
L. L. Smith ◽  
R. F. Davis ◽  
M. J. Kim ◽  
R. W. Carpenter ◽  
Y. Huang
Keyword(s):  
High Temperature ◽  
Ohmic Contacts ◽  
Microstructural Characterization ◽  
Secondary Phase ◽  
High Resolution Electron Microscopy ◽  
Contact Resistivity ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
Specific Contact Resistivity

The work described in this paper is part of a systematic study of ohmic contact strategies for GaN-based semiconductors. Gold contacts exhibited ohmic behavior on p-GaN when annealed at high temperature. The specific contact resistivity (ρc) calculated from TLM measurements on Au/p-GaN contacts was 53 Ω · cm2 after annealing at 800 °C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current-voltage (I-V) behavior in the as-deposited condition with ρc = 214 Ω · cm2. The specific contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 725 °C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, which coincided with the improvement of contact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN contact, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725 °C for 15 s. The resultant increase in contact resistance is believed to be due to the barrier effect increased by the presence of the low work function Mg metal.

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.

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