NiGe-based ohmic contacts to n-type GaAs

Furumai, Masaki; Oku, Takeo; Ishikawa, H.; Otsuki, Akira; Koide, Yasuo; Oikawa, Tetsuo; Murakami, Masanori

doi:10.1007/s11664-996-0023-2

Cited by 11 publications

(10 citation statements)

References 20 publications

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“…To reduce the contact resistance, the current transport mechanisms through the metal/GaAs interfaces of the NiGe contacts should be understood by correlating the electrical properties to the interfacial microstructure in order to obtain a guideline for preparation of low resistance NiGebased ohmic contact materials. The results obtained by Furumai et al [96] will be given below.…”

Section: Development Of Ge-based Ohmic Contact Materialsmentioning

confidence: 87%

“…Dependence of the R c values on the Ge concentration of the NiGe contacts was investigated by extending the Ge concentration beyond 43 at.% to search the optimum Ge concentration to provide the minimum R c value [96]. The R c values of the Ni (x nm)/Ge (100 nm) contacts annealed at temperatures around 600±700 8C for 5 s are plotted in Fig.…”

Section: Electrical Properties Of Nige Ohmic Contactsmentioning

confidence: 99%

“…However, further reduction of the contact resistance was requires for the future sub-micron devices. Therefore, the effects of addition of direct doping elements (Sn, Sb, and Te) and indirect doping elements (Pd, Pt, and Cu) were investigated [96] and the results will be given in the next sections.…”

Section: Effects Of Addition Of Third Elements To Nige Ohmic Contactsmentioning

confidence: 99%

“…High-resolution image of Ni (75 nm)/Ge (100 nm) contact annealed at 600 8C for 5 s, taken with the incident beam parallel to the [01 Å 0] of the GaAs substrate[96].…”

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confidence: 99%

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Development of refractory ohmic contact materials for gallium arsenide compound semiconductors

Murakami

2002

Science and Technology of Advanced Materials

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Recent strong demands for optoelectronic communication and portable telephones have encouraged engineers to develop optoelectronic devices, microwave devices, and high-speed devices using hetero-structural GaAs-based compound semiconductors. Although the GaAs crystal growth techniques had reached a level to control the compositional stoichiometry and crystal defects on a nearly atomic scale by the advanced techniques such as molecular beam epitaxy and metal organic chemical vapor deposition techniques, development of ohmic contact materials (which play a key role to inject external electric current from the metals to the semiconductors) was still on a trial-and-error basis. Our research efforts have been focused to develop low resistance, refractory ohmic contact materials to n-type GaAs using the deposition and annealing techniques, and it was found the growth of homo-or hetero-epitaxial intermediate semiconductor layers (ISL) on the GaAs surface was essential for the low resistance ohmic contact formation. In this paper, two typical examples of ohmic contact materials developed by forming ISL were given. The one was refractory NiGe-based ohmic contact material, which was developed by forming the homo-epitaxial ISL doped heavily with donors. This heavily doped ISL was discovered to be formed through the regrowth mechanism of GaAs layers at the NiGe/GaAs interfaces during annealing at elevated temperatures. To reduce the contact resistance further down to a value required by the device designers, an addition of small amounts of third elements to NiGe, which have strong binding energy with Ga, was found to be essential. These third elements contributed to increase the carrier concentration in ISL. The low resistance ohmic contact materials developed by forming homo-epitaxial ISL were Ni/M/Ge where a slash`/' denotes the deposition sequence and M is an extremely thin (,5 nm) layer of Au, Ag, Pd, Pt or In. The other was refractory In x Ga 12x As-based ohmic contact materials which were developed by forming the hetero-epitaxial ISL with low Schottky barrier to the contacting metals by growing the In x Ga 12x As layers on the GaAs substrate by sputter-depositing In x Ga 12x As targets and subsequently annealing at elevated temperatures. To reduce the contact resistance, it was found that this In x Ga 12x As (ISL) layer had to have In compositional gradient normal to the GaAs surface: the In concentration being rich at the metal/In x Ga 12x As interface and poor close to the In x Ga 12x As/GaAs interface. This concentration graded ISL reduced both the barrier heights at the metal/ISL and ISL/GaAs interfaces and reduced the contact resistance. The ohmic contact materials developed by forming heteroepitaxial ISL was In 0.7 Ga 0.3 As/Ni/WN 2 /W. These contact materials formed refractory compounds at the interfaces, which was also found to be essential to improve thermal stability of ohmic contacts used in the GaAs devices.

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Section: Development Of Ge-based Ohmic Contact Materialsmentioning

confidence: 87%

Section: Electrical Properties Of Nige Ohmic Contactsmentioning

confidence: 99%

Section: Effects Of Addition Of Third Elements To Nige Ohmic Contactsmentioning

confidence: 99%

“…High-resolution image of Ni (75 nm)/Ge (100 nm) contact annealed at 600 8C for 5 s, taken with the incident beam parallel to the [01 Å 0] of the GaAs substrate[96].…”

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confidence: 99%

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Development of refractory ohmic contact materials for gallium arsenide compound semiconductors

Murakami

2002

Science and Technology of Advanced Materials

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240

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“…23,24) For the p-InP ohmic contacts, Wang et al developed PdGe(Zn) contacts using SPR process. 4) From the XRD and XTEM study of Sb/Zn/Pd contacts, Pd in the contact materials was found to react with InP to produce ternary Pd 2 InP compounds at the contact metals/InP interface.…”

Section: Role Of Pd Third Layermentioning

confidence: 99%

Formation Mechanism of Low Contact Resistance PdZn-based Ohmic Contacts for p-type InP

et al. 2002

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Recently, Sb(3 nm)/Zn(20 nm)/Pd(20 nm) ohmic contact materials to p-type InP which provides high reliable, low contact resistance after annealing at temperature around 375 • C have been developed in our laboratories (where a slash (/) sign indicates the deposition sequence). The use of these contact materials for photodiodes made it possible to achieve simultaneous preparation of both p and n-type ohmic contacts, which resulted in significant reduction of the fabrication process steps. In the present paper in order to understand the mechanism of ohmic contact formation, the microstructural analysis of the interfaces between the Sb/Zn/Pd ohmic contacts and the Zn-doped p-type InP was carried out by X-ray diffraction, cross-sectional transmission electron microscopy, secondary ion mass spectroscopy, and electrochemical capacitancevoltage measurement. The present experiments proposed a new contact formation mechanism: reduction of the ohmic contact resistances was obtained primarily due to suppression of Zn (doped in the InP) outdiffusing from the InP substrate during annealing by the Pd 2 InP layers which contained Zn. Thus the direct contact of the Pd 2 InP layers to the InP substrate was found to be essential to prevent reduction of the net acceptor concentration near the InP surface and also to improve the thermal stability of ohmic contacts. The roles of Pd and Sb added to the contact materials also contributed to the reduction of contact resistance and their roles will be discussed.

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