Formation of extremely low resistance Ti/Pt/Au ohmic contacts to p-GaAs

Nonalloyed Ti/Pt/Au contacts to heavily doped p-GaAs have been fabricated using effective cleaning of the semiconductor surface by bombardment with low energy Ar+ ions (60 eV) prior to the metal deposition. Short-time annealing cycles for 1 and 20 s were employed in order to restore the primary properties of the subsurface layer disordered during ion bombardment. Annealing at temperatures ranging from 420 to 530 degrees C provides formation of contacts with an extremely low resistivity of 2.8*10-8 Omega cm2. A definite correlation between electrical properties and structural modifications of the contact interface was found. Measurements of the contact resistivity at different ambient temperatures yielded a good quantitative agreement with the theoretically predicted values using the field-emission model. The results indicate that the metal-semiconductor junctions formed under optimal conditions are intimate and that tunneling is the dominant mechanism of the current flow

A controllable mechanism of forming extremely low resistance nonalloyed ohmic contacts to group III V compound semiconductors

This work refers basically to the detailed understanding of the natural phenomena in real tunneling metal semiconductor contacts. A mechanism of forming extremely low resistance nonalloyed Ti Pt Au ohmic contacts to a variety of III V compound semiconductors, e.g., InGaAs, InAs; and GaAs, is presented. Epitaxial layers of either type with different doping levels ranging from 1 X 10 19 to 2 X 10 20 cm 3 were employed in order to determine electrical parameters that guarantee pure tunneling behavior of the contacts. Ti Pt Au contacts formed on p InGaAs Zn doped to 1 X 10 20 cm 3 and on n InGaAs Si doped to 5 X 10 19 cm 3 yielded a specific contact resistance of 4.8 X 10 8 and 4.3 X 10 8 OMEGA cm2, respectively. The same metallization scheme applied to 4 X 10 19 cm 3 Si doped n InAs gave a specific contact resistance of 1.7 X 10 8 OMEGA cm2 for the as deposited and annealed samples. An extremely low value of 2.8 X 10 8 OMEGA cm2 was evaluated for contacts on p GaAs doped with Be to 2 X 10 20 cm 3. The contact properties are discussed in relation to the effect of ion beam cleaning and postdeposition annealing. Of particular concern was the cleaning of the semiconductor surface with low energy 60 eV Ar ions for 40 s prior to the metallization process. This opens also the possibility to investigate ion damage defects and trap assisted increase of the depletion depth. The contact design was based on the concept that the detrimental influence of the ion beam on the semiconductor properties can be neutralized with a proper annealing. It has been demonstrated that even very rapid thermal processing for 1 s at elevated temperatures was sufficient to restore the stoichiometry in the As depleted subsurface layer arising as a result of ion damage. The fabrication sequences used provide formation of intimate contacts without interfacial films and carrier compensation effects. Optimal processing conditions have been empirically established that stimulate substantially the ohmic behavior of the contacts. It was possible to achieve an absolute control over the contact formation mechanism without crucial adjustment of annealing parameters. Closer examination of the temperature dependence of the contact resistances reveals a good agreement with the theoretical approach based on the tunneling model. Metallurgical studies of the contacts confirm their unreacted, abrupt metal semiconductor configurations if optimal annealing temperatures are used. Experimental evidence manifests a definite relationship between electrical properties and interfacial compositional modifications affected by different forming conditions. The trend for structural changes occuring at annealing temperatures above the optimal ones was found to be in correlation with the chemical reactivity of III V compounds. The observed thermal stability of the contacts can be fully explained in this way. In contrast to chemical precleaning the controllable elimination of interface inhomogeneities during ion etching results in contacts with improved homogeneity and uniformity. The demonstrated universality and reliability make the fabrication technique suitable to meet specific needs of modem semiconductor device

A reliable fabrication technique for very low resistance ohmic contacts to p-InGaAs using low energy Ar+ ion beam sputtering

A fabrication technique for non-alloyed Au/Pt/Ti ohmic contacts to p-InGaAs (NA=1*1020 cm-3) is discussed. The semiconductor surface is cleaned by Ar+ ions immediately followed by the metal deposition by electron beam evaporation. The low energy (60 eV) Ar+ ion etching removes the residual oxide layer existent on the semiconductor surface. The contact is formed by rapid thermal processing (RTP) at 400+or-C. It is shown that extremely low specific contact resistances (rc =6*10-8 Omega -cm2) can be achieved, even for 2.5 mu m contact widths, and that the contacts produced exhibit excellent homogeneity and improved uniformity over wet chemically pre-cleaned ones

Photonik - Optische Kommunikationstechnik (Schluesselbauelemente). Langwellige Laserdioden mit Vertikalresonator Schlussbericht

Available from TIB Hannover: DtF QN1(90,41) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman