Development of refractory ohmic contact materials for gallium arsenide compound semiconductors

Abstract 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 InxGa1-xAs-basedohmic contact materials which were developed by forming the hetero-epitaxial ISL with low Schottky barrier to the contacting metals by growing the InxGa1-xAs layers on the GaAs substrate by sputter-depositing InxGa1-xAs targets and subsequently annealing at elevated temperatures. To reduce the contact resistance, it was found that this InxGa1-xAs (ISL) layer had to have In compositional gradient normal tothe GaAs surface: the In concentration being rich at the metal/InxGa1-xAs interface and poor close to the InxGa1-xAs/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 hetero-epitaxial ISL was In0.7Ga0.3As/Ni/WN2/W. These contact materials formed refractory compounds atthe interfaces, which was also found to be essential to improve thermal stability of ohmic contacts used in the GaAs devices.

[1]  G. Y. Robinson,et al.  Schottky Diodes and Ohmic Contacts for the III-V Semiconductors , 1985 .

[2]  Alessandro C. Callegari,et al.  Uniform and thermally stable AuGeNi ohmic contacts to GaAs , 1985 .

[3]  T. Sands,et al.  In/GaAs reaction: Effect of an intervening oxide layer , 1986 .

[4]  J. Oswald,et al.  Heavy doping with Sn of GaAs layers grown by molecular beam epitaxy for non-alloyed ohmic contacts , 1988 .

[5]  N. Ono,et al.  Formation mechanism of InxGa1−xAs ohmic contacts to n-type GaAs prepared by radio frequency sputtering , 1994 .

[6]  N. Braslau,et al.  Metal-semiconductor contacts for GaAs bulk effect devices , 1967 .

[7]  T. Sands,et al.  Ni, Pd, and Pt on GaAs: A comparative study of interfacial structures, compositions, and reacted film morphologies , 1987 .

[8]  Osaake Nakajima,et al.  Non-Alloyed Ohmic Contacts to n-GaAs Using Compositionally Graded InxGa1-xAs Layers , 1988 .

[9]  P. Sircar.  Laser annealed ohmic contact to n+-GaAs , 1983 .

[10]  Y. Koide,et al.  NiGe-based ohmic contacts to n-type GaAs , 1996 .

[11]  M. B. Das,et al.  The characteristics of AuGe-based ohmic contacts to n-GaAs including the effects of aging , 1983 .

[12]  A. G. Nassibian,et al.  Dependence of ohmic contact quality on Au−Ge alloy thickness for n-type GaAs , 1984 .

[13]  Yoshihiko Mizushima,et al.  Schottky barrier height of n‐InxGa1−xAs diodes , 1973 .

[14]  C. R. Crowell,et al.  Normalized thermionic-field (T-F) emission in metal-semiconductor (Schottky) barriers , 1969 .

[15]  A. Y. Cho,et al.  Film Deposition by Molecular-Beam Techniques , 1971 .

[16]  R. P. Gupta,et al.  Metallization systems for ohmic contacts to p- and n-type GaAs , 1979 .

[17]  F. R. de Boer,et al.  Model predictions for the enthalpy of formation of transition metal alloys II , 1977 .

[18]  O. Aina,et al.  SIMS analysis of low temperature ohmic contacts to GaAs , 1981 .

[19]  A. Iliadis,et al.  Metallurgical behaviour of Ni/AuGe ohmic contacts to GaAs , 1984 .

[20]  T. Jackson,et al.  Electron microscope studies of an alloyed Au/Ni/Au‐Ge ohmic contact to GaAs , 1983 .

[21]  S. Mitsui,et al.  Growth temperature dependence in molecular beam epitaxy of gallium arsenide , 1978 .

[22]  M. Murakami,et al.  NiGe‐based ohmic contacts to n‐type GaAs. II. Effects of Au addition , 1994 .

[23]  R. H. Cox,et al.  Ohmic contacts for GaAs devices , 1967 .

[24]  V. L. Rideout,et al.  A review of the theory and technology for ohmic contacts to group III–V compound semiconductors , 1975 .

[25]  N. Ono,et al.  InxGa1-xAs ohmic contacts to n-type GaAs prepared by sputter deposition , 1995 .

[26]  H. Raidt,et al.  The importance of the Ni to Ge ratio and of the annealing cycle for the resistivity and morphology of NiAuGe ohmic contacts to n-GaAs , 1987 .

[27]  W. H. Price,et al.  Thermally stable ohmic contacts to n‐type GaAs. IV. Role of Ni on NiInW contacts , 1989 .

[28]  Carver A. Mead,et al.  Fermi Level Position at Metal-Semiconductor Interfaces , 1964 .

[29]  T. Jackson,et al.  Low‐resistance nonalloyed ohmic contacts to Si‐doped molecular beam epitaxial GaAs , 1985 .

[30]  M. Murakami.  Development of ohmic contact materials for GaAs integrated circuits , 1990 .

[31]  W. Tsang.  In situ Ohmic‐contact formation to n‐ and p‐GaAs by molecular beam epitaxy , 1978 .

[32]  H. Wieder.  Fermi level and surface barrier of GaxIn1−xAs alloys , 1981 .

[33]  Z. A. Munir,et al.  Interfacial properties governing ohmic contacts between gold alloys and oriented gallium arsenide crystals , 1975 .

[34]  J. Waldrop,et al.  Correlation of interface composition and barrier height for model AuGeNi contacts to GaAs , 1987 .

[35]  J. Mercier,et al.  Formation, microstructure et résistances des contacts AuGe/n-GaAs, AuGe/n-InP, AuZn/p-InP et AuBe/p-InP , 1985 .

[36]  T. Sands,et al.  An investigation of the Pd‐In‐Ge nonspiking Ohmic contact to n‐GaAs using transmission line measurement, Kelvin, and Cox and Strack structures , 1991 .

[37]  A. Christou,et al.  Laser annealed Ta/Ge and Ni/Ge ohmic contacts to GaAs , 1981, IEEE Electron Device Letters.

[38]  Horst H. Berger,et al.  Models for contacts to planar devices , 1972 .

[39]  M. Ogawa.  Alloying behavior of Ni/Au‐Ge films on GaAs , 1980 .

[40]  K. Heime,et al.  Very low resistance Ni_AuGe_Ni contacts to n-GaAs , 1974 .

[41]  M. Murakami,et al.  NiGe‐based ohmic contacts to n‐type GaAs. I. Effects of In addition , 1994 .

[42]  M. Murakami,et al.  Thermally stable non‐gold Ohmic contacts to n‐type GaAs. I. NiGe contact metal , 1992 .

[43]  G. Antypas.  Liquid‐Phase Epitaxy of In × GA 1 − × As , 1970 .

[44]  A. B. Torrens,et al.  Specific contact resistance of ohmic contacts to gallium arsenide , 1972 .

[45]  W. H. Price,et al.  Thermally stable ohmic contacts to n-type GaAs. III. GeInW and NiInW contact metals , 1988 .

[46]  Thomas F. Kuech,et al.  Nonalloyed ohmic contacts to n-GaAs by solid-phase epitaxy of Ge , 1987 .

[47]  Williams,et al.  Electrical study of Schottky barriers on atomically clean GaAs(110) surfaces. , 1986, Physical review. B, Condensed matter.

[48]  N. Ono,et al.  InxGa1 − xAs-based Ohmic contacts to n-type GaAs with W-nitride barrier prepared by radio frequency sputtering , 1997 .

[49]  M. Otsubo,et al.  Liquid phase epitaxial growth of GaAs from AuGeNi melts , 1977 .

[50]  Y. Mori,et al.  Investigation of orientation effect on contact resistance in selectively doped AlGaAs/GaAs heterostructures , 1986 .

[51]  M. Ogawa.  Alloying reaction in thin nickel films deposited on GaAs , 1980 .

[52]  A. Cho,et al.  Nonalloyed Ohmic contacts to n‐GaAs by molecular beam epitaxy , 1978 .

[53]  R. Stratton,et al.  Differential resistance peaks of Schottky barrier diodes , 1967 .

[54]  D. Chung,et al.  In situ X-ray diffraction study of the effects of germanium and nickel concentrations on melting in gold-based contacts to gallium arsenide , 1987 .

[55]  R. Ball.  Improvements in the topography of AuGeNi-based ohmic contacts to n-GaAs , 1989 .

[56]  M. Murakami,et al.  Development of InxGa1−xAs-based ohmic contacts for p-type GaAs by radio-frequency sputtering , 1998 .

[57]  G. Mcguire,et al.  Investigation of the Ag In Ge system used for alloyed contacts to GaAs , 1979 .

[58]  E. H. Rhoderick,et al.  Metal–Semiconductor Contacts , 1979 .

[59]  Alessandro C. Callegari,et al.  Effects of interfacial microstructure on uniformity and thermal stability of AuNiGe ohmic contact to n-type GaAs , 1987 .

[60]  E. Kuphal.  Liquid phase epitaxy , 1991 .

[61]  H. Chung,et al.  Damage induced by CHF3+C2F6 plasma etching on Si‐implanted GaAs(100) , 1987 .

[62]  A. Lakhani,et al.  Application of a resonant tunnelling structure to demonstrate subsurface damage and surface migration on InGaAs during AuGe contact anneal , 1988 .

[63]  O. W. Holland,et al.  Rapid thermal annealing of ion‐implanted semiconductors , 1984 .

[64]  G. Y. Robinson,et al.  Metallurgical and electrical properties of alloyed Ni/AuGe films on n-type GaAs , 1975 .

[65]  J. G. Werthen,et al.  Ohmic contacts to n‐GaAs using low‐temperature anneal , 1981 .

[66]  T. Sands,et al.  Initial stages of the Pd−GaAs reaction: formation and decomposition of ternary phases , 1986 .

[67]  A. Cho,et al.  Epitaxy of silicon doped gallium arsenide by molecular beam method , 1971 .

[68]  Carl W. Wilmsen,et al.  Physics and chemistry of III-V compound semiconductor interfaces , 1985 .

[69]  J. Malherbe,et al.  Formation of ohmic contacts to n-GaAs by ion beam mixing and annealing , 1988 .

[70]  B. A. Joyce,et al.  Tin‐doping effects in GaAs films grown by molecular beam epitaxy , 1978 .

[71]  J. Mayer,et al.  Alloying Behavior of Au and Au–Ge on GaAs , 1971 .

[72]  R. E. Viturro,et al.  Low‐temperature formation of metal/molecular‐beam epitaxy‐GaAs(100) interfaces: Approaching ideal chemical and electronic limits , 1989 .

[73]  Donald F. Hewitt.  A partial study of the NiAs-NiSb system , 1948 .

[74]  R. Bruce,et al.  An improved AuGeNi ohmic contact to n-type GaAs , 1987 .

[75]  H. Hartnagel,et al.  Supersaturation requirement for good ohmic contacts to semiconductors , 1976 .

[76]  C. Grovenor.  Au/Ge based ohmic contacts to GaAs , 1981 .

[77]  J. Gunn.  The discovery of microwave oscillations in gallium arsenide , 1976, IEEE Transactions on Electron Devices.

[78]  M. Eizenberg,et al.  Interfacial reactions between Ni films and GaAs , 1986 .

[79]  R. Stratton,et al.  Field and thermionic-field emission in Schottky barriers , 1966 .

[80]  K. Shenai.  Very low resistance nonalloyed ohmic contacts to Sn-doped molecular-beam epitaxial GaAs , 1987, IEEE Transactions on Electron Devices.

[81]  Y. G. Chai,et al.  The effect of growth conditions on Si incorporation in molecular beam epitaxial GaAs , 1981 .

[82]  S. Wright,et al.  Absence of Fermi level pinning at metal‐InxGa1−xAs(100) interfaces , 1986 .

[83]  O. Aina,et al.  Low‐temperature sintered AuGe/GaAs ohmic contact , 1982 .

[84]  J. Waldrop.  Schottky‐barrier height of ideal metal contacts to GaAs , 1984 .

[85]  A. G. Nassibian,et al.  Ultrathin-film ohmic contacts for GaAs FET , 1983 .

[86]  M. Procop,et al.  Au-ge based ohmic contacts on GaAs , 1986 .

[87]  W. H. Price,et al.  Development of Thermally Stable Indium-Based Ohmic Contacts to N-Type GaAs , 1989 .

[88]  W. Hume-rothery,et al.  The equilibrium diagram of the system gold-gallium , 1966 .

[89]  N. Ono,et al.  InxGa1−xAs ohmic contacts to n-type GaAs with a tungsten nitride barrier , 1997 .

[90]  A. Callegari,et al.  Microstructure studies of AuNiGe Ohmic contacts to n‐type GaAs , 1986 .

[91]  A. G. Nassibian,et al.  Scanned electron beam alloyed ohmic contacts to n-GaAs , 1987 .

[92]  A. Yariv,et al.  Q‐switched ruby laser alloying of Ohmic contacts on gallium arsenide epilayers , 1978 .

[93]  David J. Webb,et al.  Characterization of GaAs self‐aligned refractory‐gate metal‐semiconductor field‐effect transistor (MESFET) integrated circuits , 1987 .

[94]  M. B. Das,et al.  The effects of contact size and non-zero metal resistance on the determination of specific contact resistance , 1982 .

[95]  K. Kaneko,et al.  Excimer‐laser annealed ohmic contacts to n‐GaAs substrates through an ultrathin reacted layer , 1987 .

[96]  A. Yu,et al.  Electron tunneling and contact resistance of metal-silicon contact barriers , 1970 .

[97]  Chun-Yen Chang,et al.  Specific contact resistance of metal-semiconductor barriers , 1971 .

[98]  間庭 秀世,et al.  Max Hansen and Kurt Anderko: Constitution of Binary Alloys. McGraw-Hill Book Co., New York, 1958, 1305頁, 23×16cm, \13.000. , 1958 .

[99]  H. G. Henry,et al.  Hot-plate alloying for ohmic contacts to GaAs , 1984, IEEE Transactions on Electron Devices.

[100]  J. Waldrop,et al.  Variation of n‐GaAs (100) interface Fermi level by Ge and Si overlayers , 1987 .

[101]  N. Bloembergen,et al.  Laser and Electron Beam Interactions with Solids , 1982 .

[102]  P. Sircar.  Excimer laser annealed gold and silver ohmic contacts on+‐GaAs , 1986 .

[103]  T. Jung,et al.  Interdiffusion Profiles of AuGe/n‐GaAs Ohmic Contacts Studied by AES , 1983 .

[104]  S. Oktyabrsky,et al.  Microstructure characterization of Cu3Ge/n‐type GaAs ohmic contacts , 1994 .

[105]  S. M. Sze,et al.  Physics of semiconductor devices , 1969 .

[106]  I. Lindau,et al.  Unified Mechanism for Schottky-Barrier Formation and III-V Oxide Interface States , 1980 .

[107]  T. Jackson,et al.  Ohmic contacts to n‐GaAs using graded band gap layers of Ga1−xInxAs grown by molecular beam epitaxy , 1981 .

[108]  C. Wilkinson,et al.  Low‐temperature annealed contacts to very thin GaAs epilayers , 1986 .

[109]  A. Cho.  Impurity profiles of GaAs epitaxial layers doped with Sn, Si, and Ge grown with molecular beam epitaxy , 1975 .

[110]  A. Callegari,et al.  Electrical and thermal stability of AuGeNi ohmic contacts to GaAs fabricated with in situ RF sputter cleaning , 1986 .

[111]  A. G. Nassibian,et al.  Backscattering analysis of AuGe-Ni ohmic contacts of n-GaAs , 1986 .

[112]  M. Hansen,et al.  Constitution of Binary Alloys , 1958 .

[113]  D. Chung,et al.  The effects of germanium concentration on the compound formation and morphology of gold‐based contacts to gallium arsenide , 1986 .

[114]  W. H. Price,et al.  Thermally stable ohmic contacts to n‐type GaAs. VI. InW contact metal , 1998 .