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.

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.

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.

Effect of Au distribution in NiO/Au film on the ohmic contact formation to p-type GaN

2005 ◽  
Vol 20 (2) ◽  
pp. 456-463 ◽  
Author(s):  
Jiin-Long Yang ◽  
J.S. Chen ◽  
S.J. Chang
Keyword(s):  
Electron Microscopy ◽  
Ohmic Contact ◽  
Incident Angle ◽  
Specific Contact Resistance ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Specific Contact ◽  
P Type

The distribution of Au and NiO in NiO/Au ohmic contact on p-type GaN was investigated in this work. Au (5 nm) films were deposited on p-GaN substrates by magnetron sputtering. Some of the Au films were preheated in N2 ambient to agglomerate into semi-connected structure (abbreviated by agg-Au); others were not preheated and remained the continuous (abbreviated by cont-Au). A NiO film (5 nm) was deposited on both types of samples, and all samples were subsequently annealed in N2 ambient at the temperatures ranging from 100 to 500 °C. The surface morphology, phases, and cross-sectional microstructure were investigated by scanning electron microscopy, glancing incident angle x-ray diffraction, and transmission electron microscopy. I-V measurement on the contacts indicates that only the 400 °C annealed NiO/cont-Au/p-GaN sample exhibits ohmic behavior and its specific contact resistance (ρc) is 8.93 × 10−3 Ω cm2. After annealing, Au and NiO contact to GaN individually in the NiO/agg-Au/p-GaN system while the Au and NiO layers become tangled in the NiO/cont-Au/p-GaN system. As a result, the highly tangled NiO-Au structure shall be the key to achieve the ohmic behavior for NiO/cont-Au/p-GaN system.

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.

An investigation of a nonspiking Ohmic contact to n-GaAs using the Si/Pd system

1988 ◽  
Vol 3 (5) ◽  
pp. 922-930 ◽  
Author(s):  
L. C. Wang ◽  
B. Zhang ◽  
F. Fang ◽  
E. D. Marshall ◽  
S. S. Lau ◽  
...  
Keyword(s):  
Ohmic Contact ◽  
Rutherford Backscattering Spectrometry ◽  
Tunneling Current ◽  
Solid State Reactions ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Specific Contact ◽  
Diffraction Patterns ◽  
Ohmic Contact Formation

A low-resistance nonspiking Ohmic contact to n-GaAs is formed via solid-state reactions utilizing the Si/Pd/GaAs system. Samples with Si to Pd atomic ratios greater than 0.65 result in specific contact resistivity of the order of 10−6 Ω cm2, whereas samples with atomic ratios less than 0.65 yield higher specific contact resistivities or rectifying contacts. Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, and electron diffraction patterns show that a Pd, Si layer is in contact with GaAs with excess Si on the surface after the Ohmic formation annealing. This observation contrasts with that on a previously studied Ge/Pd/GaAs contact where Ohmic behavior is detected after transport of Ge through PdGe to the interface with GaAs. Comparing the Ge/Pd/GaAs system with the present Si/Pd/GaAs system suggests that a low barrier heterojunction between Ge and GaAs is not the primary reason for Ohmic contact behavior. Low-temperature measurements suggest that Ohmic behavior results from tunneling current transport mechanisms. A regrowth mechanism involving the formation of an n+ GaAs surface layer is proposed to explain the Ohmic contact formation.

Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN

1999 ◽  
Vol 14 (3) ◽  
pp. 1032-1038 ◽  
Author(s):  
L. L. Smith ◽  
R. F. Davis ◽  
R-J. Liu ◽  
M. J. Kim ◽  
R. W. Carpenter
Keyword(s):  
Photoelectron Spectroscopy ◽  
Room Temperature ◽  
Ohmic Contacts ◽  
Tem Analysis ◽  
Cross Sectional ◽  
X Ray ◽  
Transmission Electron ◽  
Specific Contact ◽  
Contact Resistivities ◽  
Thermal Stability Of

Single Ti layers, single TiN layers, and thin Ti films overlayered with Au were investigated as ohmic contacts to n-type (n 4.5 × 1017 to 7.4 × 1018 cm−3) single-crystal GaN (0001) films. Transmission line measurements (TLM) revealed the as-deposited TiN and Au/Ti contacts on n = 1.2 − 1018 cm−3 to be ohmic with room-temperature specific contact resistivities of 650 and 2.5 × 107minus;5 Ω cm2, respectively. Single Ti layer contacts had high resistance and were weakly rectifying in the as-deposited condition. The three contact/GaN systems exhibited a substantial decrease in resistivity after annealing; the value of ρc was also a function of the carrier concentration in the GaN. The Au/Ti contacts exhibited the lowest resistivity values yet observed in these contact studies, particularly for the more lightly doped n-GaN. The ρc for n = 1.2 × 1018 cm−3 reached 1.2 × 1026 Ω cm2; for n = 4.5 × 1017 cm−3, ρc = 7.5 × 1025 Ω cm2 after annealing both samples through 900 °C. X-ray photoelectron spectroscopy (XPS) and high-resolution cross-sectional transmission electron microscopy (X-TEM) analysis revealed the formation of TiN at the interface of annealed Ti layers in contact with GaN, which is believed to be beneficial for ohmic contact performance on n-GaN.

Microstructure, electrical properties, and thermal stability of Al ohmic contacts to n-GaN

1996 ◽  
Vol 11 (9) ◽  
pp. 2257-2262 ◽  
Author(s):  
L. L. Smith ◽  
R. F. Davis ◽  
M. J. Kim ◽  
R. W. Carpenter ◽  
Y. Huang
Keyword(s):  
Room Temperature ◽  
Ohmic Contacts ◽  
Secondary Phase ◽  
High Resolution Electron Microscopy ◽  
Contact Resistivity ◽  
Cross Sectional ◽  
Resolution Electron ◽  
Secondary Phase Formation ◽  
Specific Contact ◽  
Diffraction Patterns

As-deposited Al contacts were ohmic with a room-temperature contact resistivity of 8.6 × 10−5 Ω · cm2 on Ge-doped, highly n-type GaN (n = 5 × 1019 cm−3). They remained thermally stable to at least 500 °C, under flowing N2 at atmospheric pressure. The specific contact resistivities (ρc) calculated from TLM measurements on as-deposited Al layers were found to range from 8.6 × 10−5 Ω · cm2 at room temperature and 6.2 × 10−5 Ω · cm2 at 500 °C. Annealing treatments at 550 °C and 650 °C for 60 s each under flowing N2 resulted in an overall increase of contact resistivity. Cross-sectional, high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, and coincided with the degradation of contact performance. Electron diffraction patterns from the particles revealed a cubic structure with lattice constant a = 0.784 nm, and faceting occurring on the {100} faces. Spectroscopic analysis via electron energy loss spectroscopy (EELS) revealed the presence of nitrogen and small amounts of oxygen in the Al layer, but no appreciable amounts of Ga. The results of microstructural and crystallographic characterization indicate that the new interfacial phase is a type of spinel Al nitride or Al oxynitride.

Investigation of Ge, As, and Au Diffusion in Non-Alloyed Epitaxial Au-Ge Ohmic Contacts to n-GaAs Using Secondary Ion Mass Spectroscopy Backside Sputter Depth-Profiling

1991 ◽  
Vol 240 ◽  
Author(s):  
H. S. LEE ◽  
R. T. Lareau ◽  
S. N. Schauer ◽  
R. P. Moerkirk ◽  
K. A. Jones ◽  
...  
Keyword(s):  
Ohmic Contacts ◽  
Ion Beam ◽  
Depth Profiling ◽  
Depth Resolution ◽  
High Concentration ◽  
Ohmic Behavior ◽  
Preferential Sputtering ◽  
Specific Contact ◽  
Secondary Ion ◽  
Diffusion Profiles

ABSTRACTA SIMS backside sputter depth-profile technique using marker layers is employed to characterize the diffusion profiles of the Ge, As, and Au in the Au-Ge contacts after annealing at 320 C for various times. This technique overcomes difficulties such as ion beam mixing and preferential sputtering and results in high depth resolution measurements since diffusion profiles are measured from low to high concentration. Localized reactions in the form of islands were observed across the surface of the contact after annealing and were composed of Au, Ge, and As, as determined by SIMS imaging and Auger depth profiling. Backside SIMS profiles indicate both Ge and Au diffusion into the GaAs substrate in the isalnd regions. Ohmic behavior was obtained after a 3 hour anneal with a the lowest average specific contact resistivity found to be ∼ 7 × 100−6 Ω- cm2.

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.

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