The structure and properties of metal-semiconductor interfaces

Alloying behavior of thin Ni/Au‐Ge films deposited on a GaAs substrate is investigated by using a microprobe Auger spectrometer and an x‐ray diffractometer. The deposited films react with the substrate above 300 °C to form alloys with complex multilayer structure in the 300–400 °C temperature range and alloys with microscopic grain structure above 450 °C. Uniform alloying, accompanied with a smooth interface, is observed and is ascribed to the high reactivity of Ni with GaAs under a solid‐solid phase. However, when the sample is annealed in the solid‐solid phase, Ni penetrates irregularly into the GaAs substrate, if the annealing duration is too long, causing poor Ohmicity. Rapid Ge moving to the substrate interface is observed at 400 °C and is closely related to the formation of a Ge‐doped degenerate layer beneath the contact. The high reliability of the contract, which is obtained when annealed at 500 °C, is explained by the metallurgical stability of the grain structure. Based on the results of this study, some rules for III‐V compound semiconductor contact fabrication are proposed.

Alloying behavior of Ni/Au‐Ge films on GaAs

We have studied AuGeNi ohmic contacts to n-type MBE grown GaAs epitaxial-layer with doping in the (1016−1019) cm−3 range, and found several new effects: (a) Contact resistivity exhibit a weak dependence on carrier concentration (much weaker than 1/ND depencence); (b) We find evidence for a high resistivity layer under the contact at least several thousands angstroms deep, which dominate the contact resistance in most cases; (c) We find a peripheral zone around the contact, about 1 μm wide which differs chemically from the GaAs epi-layer; (d) SIMS analysis reveals a deep diffusion into the GaAs of Ni and Ge; (e) Correlation between density of GeNi clusters in the contact and the contact resistivity are found; (f) Temperature measurements justify that tunneling is responsible for the ohmic contact. We discuss also the validity of the transmission line method and the commonly accepted model of the contact.

Characteristics of AuGeNi ohmic contacts to GaAs

This work is devoted to a mass spectrometric study of volatile component loss and in situ measurement of the resistance of metallized GaAs and GaP samples during heat treatment. Arsenic losses during heat treatment have been determined quantitatively with a quadrupole mass spectrometer. A relation was found between the arsenic loss and the specific contact resistance of the metallized sample. The associated activation energy was found to be similar to the case of thin film diffusion.

Volatile component loss and contact resistance of metals on GaAs and GaP during annealing

The Richardson constants for near-ideal AuGaAs and AlGaAs Schottky diodes have been determined from an analysis of forward current-voltage characteristics. Measurement of capacitance-voltage characteristics at different temperatures shows that the barrier heights of the diodes have very similar temperature dependence for both Au and Al contacts. On taking into account the temperature dependence of the barrier height, the corrected value of the Richardson constant for AuGaAs diode is found to be very close to the predicted theoretical value. The corresponding value for AlGaAs diode is about a factor of five smaller which is explained on the basis of a thin interfacial layer between Al and GaAs.

Measurement of Richardson constant of GaAs Schottky barriers

The results of an experimental study of the interdiffusion occurring at elevated temperatures in Au/GaAs and Ni/Au–Ge/GaAs thin‐film systems and of the corresponding changes in the Schottky barrier energy φBn are presented. Composition‐depth profiles obtained with Auger electron spectroscopy and in situ sputter etching are used to observe the interdiffusion behavior. For Au/GaAs samples, significant Ga outdiffusion and surface accumulation is found along with appreciable lowering of φBn with increasing heat treatment. For an ohmic contact consisting of Ni/Au–Ge/GaAs, Ni moves through the Au–Ge layer to produce an increase in φBn at temperatures below the Au–Ge eutectic point. Considerable intermixing of all constituents of the Ni/Au–Ge/GaAs system is found to occur above the Au–Ge eutectic temperature.

G. Y. Robinson

Papers

Variation of Schottky‐barrier energy with interdiffusion in Au and Ni/Au–Ge films on GaAs