Ohmic Contact Metallization Research Articles

Extremely low contact resistances for AlGaAs/GaAs modulation-doped field-effect transistor structures

We report contact resistances as low as 0.035 Ω mm between the ohmic contact metal and the two-dimensional electron gas channel in an AlGaAs-GaAs modulation-doped field-effect transistor structure. The contact resistances are achieved by transient annealing of AuGe/Ni/Au, and are to our knowledge the smallest values reported to date for these structures at room temperature. Assuming no change in the semiconductor sheet resistivity under the metal contact, the calculated specific contact resistivity would be as low as 5×10−8 Ω cm2, however, the true figure is not known. Details of our contact study include varying temperature-time cycles and heterojunction structures. Current-voltage measurements at 77 K show ohmic behavior, revealing the destruction of the heterojunction barrier in the contact region. Preliminary Auger energy spectroscopy profiles support an intermixing of the metal and semiconductor constituents down through the original AlGaAs-GaAs interface. We, therefore, propose a model where the current flows laterally from grains (formed during annealing) into the two-dimensional electron gas.

Evaluation of Various Electrode Metals for Ultra-High Purity P-Type Si Surface Barrier Detectors

Metal contacts on UHP p-Si were experimentally investigated. Au was evaporated at the back face of a UHP p-Si wafer to form the ohmic contact. On its front face, electrodes of 11 different metals-Pd, Ag, Au, Ni, Bi, Pb, Sn, Al, Mn, Mg and Sm were evaporated with each electrode area of 0.5 cm2, and the detector characteristics were measured. Mg, Al, Sn and Mn showed satisfactory characteristics as the barrier metal; and Pd, Au and Ni as the ohmic contact metal. Obvious correlation is observed between current characteristics and metal work function values. Carrier injection in totally depleted detectors were also studied for several back contact metals.

The characteristics of AuGe-based ohmic contacts to n-GaAs including the effects of aging

We have investigated and compared the characteristics of Au:Ge, Ni/Au:Ge and Au/Ni/Au:Ge ohmic contact metallizations to ion-implanted and epitaxial n-GaAs layers on semi-insulting substrates. Auger depth profiles of ohmic contacts and SEM of surface microstructures have provided significant insight as to the nature and degradation mechanism of ohmic contacts with aging. An electrolytic tank model with distributed resistors representing nodular or cluster form contacts has been successfully used to understand the effects of non-uniform ohmic contacts. A small degree of change in the semiconductor sheet resistance in the gaps between contacts, with aging at an elevated temperature, has been attributed to possible lateral surface diffusion of Au in the Au:Ge contacts and Ge in the Ni/Au:Ge and Au/Ni/Au:Ge contacts.

Metallurgical Behavior of Gold‐Based Ohmic Contacts to the InP / InGaAsP Material System

The performance and reliability of semiconductor devices depend critically on the electrical quality and stability of the metal contacts. Gold‐based metallizations are generally used to form ohmic contacts and Schottky barriers to the III–V material systems. In this paper, we study the interfacial reaction of Be‐Au and Sn‐Au ohmic contact metallizations on ,, and . Staining, cathodoluminescence imaging, and x‐ray microanalysis are used to analyze the metallurgical interactions. Under typical alloying conditions for ohmic contact formation (420°C for 10 min), the depth of metal‐semiconductor interaction is found to depend on the amount of gold deposited. For the same thickness of contact metallization, this depth is largest for , followed by and then . Analysis of LED's shows that the 3 μm thick Sn‐Au n‐contact penetrates ∼3 μm into the window layer. The 2.9 kÅ thick Be‐Au p‐contact completely penetrates the contact layer which is typically 0.5 μm of or .

Laser annealed Ta/Ge and Ni/Ge ohmic contacts to GaAs

Refractory metal ohmic contacts to n-type GaAs have been developed using epitaxial Ge films and pulsed laser annealing. Laser annealing was carried out with a 22 ns pulse from a Q-switched ruby laser operating in the TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> mode. The specific contact resistivity of the contacts Ta/Ge and Ni/Ge on 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> dopes GaAs exhibited sharp minima as a function of laser energy density at 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> Ω-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> Ω-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, which occurred near the melting point of the layered contacts. Auger electron sputter profiles revealed Ge migration into the GaAs surface after laser annealing at sufficient energy density to form ohmic contact. The contacts have applications to high temperature devices and to devices which experience high channel or contact temperatures, such as power FETs and TEDs.

Use of Ga in metal-GaAs contacts to eliminate large As loss peaks

Arsenic losses from Schottky and ohmic metal contacts to GaAs were quantitatively determined by a quadrupole mass spectrometer as a function of linearly increasing temperature. By adding gallium to the contact metal, the giant peaks found in the arsenic losses could be completely eliminated and the arsenic evaporation losses greatly reduced.

The Alloying of Gold and Gold Alloy Ohmic Contact Metallizations with Gallium Arsenide

The alloying of gallium arsenide with thin films of pure gold and the gold 12% germanium‐silver‐gold ohmic contact metallization used for a FET, has been investigated using optical and scanning electron microscopy. The heating rate and maximum temperature attained during heat‐treatment was found to govern the morphology of the pure gold films, and to a lesser extent the ohmic contact metallizations. The alloying cycle commences with decomposition of the underlying and diffusion of gallium into the metal at about 260°C. Melting commences above about 480°C with pure gold and 360°C with the contact metallization. The final gallium content of the metal increases as the temperature is increased and the solidification temperature of both a pure gold and multicomponent contact heated to 525°C is . The interface is very irregular consisting of approximately rectangular depressions, often over 1 μm deep, filled with metal.

Ohmic Noble Metal Contacts to Semiconducting Oxides

Noble metals deposited on semiconducting BaTiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> form blocking contacts. An ohmic behavior is obtained, if an intermediate layer of highly conducting In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> is inserted between the semiconductor and the metal. Aging of the latter contact is observed at various temperatures up to 973 K. The lower contact resistance of the system with an In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> layer is explained by the removal of oxygen being adsorbed at the surface of the semiconductor and a consequent elimination of a depletion layer.

Submicrometer self-aligned dual-gate GaAs FET

Experimental results show that it is possible to fabricate dual-gate GaAs FET's, with L g1 = 0.6 µm and L g2 = 1.3 µm, using conventional photoprocessing equipment, masks, and alignment tolerances. The initial source mesa establishes both the source and drain edges during the ohmic contact metal deposition. These two edges establish the lengths and positions of the two gates in the channel, during the two subsequent evaporations. Initial experimental devices gave reasonably good small-signal microwave performance: 8-dB packaged net gain with less than 6-dB simultaneous noise figure, at 6 GHz.