We propose a classification scheme for phase equilibria in elemental metal‐gallium‐arsenic systems. Using available data we assign as many metals as possible to seven generic types of ternary phase diagrams. We describe how the phase diagrams can provide a framework for interpreting previous studies of metal reactions with GaAs substrates and for identifying stable materials for GaAs metallizations.

Phase equilibria in metal‐gallium‐arsenic systems: Thermodynamic considerations for metallization materials

Thin film compound phase formation sequence: An effective heat of formation model

Since 1984, significant progress has been made in applying metallurgical principles and approaches to the technological problems associated with metallic contacts to compound semiconductor devices. In this paper, the field of compound semiconductor contact metallurgy is reviewed with emphasis on the role of limited solid phase reactions in the formation of doped and alloyed contacts to n-type GaAs. Specific topics include (i) the phase diagram approach to predicting metalGaAs reaction products, (ii) the effects of metal bond strength, interfacial oxide layers and the relative diffusivities of the reacting species on the reaction kinetics and reacted film morphology, (iii) the doping of GaAs by solid phase consumption and regrowth reactions to fabricate ohmic contacts and (iv) the alloying of GaAs by reactions with intermetallic phases to produce low barrier ohmic contacts and high barrier rectifying contacts. Finally, the evolution of metallic films from relatively passive contacts to active device elements is highlighted by a discussion of the recent development of stable monocrystalline intermetallic films for application as buried metal layers in ballistic and quantum effect devices.

Compound semiconductor contact metallurgy

The effect of annealing on the electrical characteristics of epitaxial aluminum/gallium arsenide Schottky barriers prepared by molecular‐beam epitaxy has been studied and compared with the annealing behavior of polycrystalline aluminum contacts deposited in a conventional evaporation system. It was found that the epitaxial contacts showed remarkably stable electrical characteristics, the forward characteristics remaining exponential over 6 decades of current after annealing for 1 h at 500 °C, with a slight degradation of n value from 1.01 to 1.02 and a very small recombination component. In the reverse direction, the characteristics improved on annealing, with a reduction in current from 9×10−10 to 6×10−11 A at a reverse bias of 1 V. In contrast, the polycrystalline contacts showed a pronounced recombination component after annealing, with an increase in n to between 1.05 and 1.09, and a significant degradation in reverse characteristics. Auger depth profiling showed that the epitaxial contacts exhibited ...

Thermal stability of epitaxial Al/GaAs Schottky barriers prepared by molecular-beam epitaxy

A metallurgically stable and laterally uniform contact to n‐GaAs with an enhanced barrier height (0.99 V) and an ideality factor of 1.10 has been achieved with a NiAl bimetallic metallization. This barrier height, as measured by the forward current‐voltage technique after annealing for 20 s at 650 °C, is higher than the reported barrier heights of refractory metallizations to n‐GaAs. Auger electron spectroscopy (AES) sputter profiles reveal an Al‐Ga exchange reaction after high‐temperature (500–950 °C) rapid thermal annealing. From these results, the barrier height enhancement is attributed to the formation of an Al1−xGaxAs layer at the NiAl/n‐GaAs interface. The thermal stability and low electrical resistivity of the NiAl phase, the enhanced barrier height on n‐GaAs, and the ease of patterning the as‐deposited Ni/Al/Ni layered structure by lift‐off techniques make NiAl a very promising gate contact material for GaAs metal‐semiconductor field‐effect transistors and related devices.

NiAl/n‐GaAs Schottky diodes: Barrier height enhancement by high‐temperature annealing

Al‐GaAs interdiffusion at temperatures between 250 and 450 °C has been studied using Auger electron spectroscopy. Ga has been observed to migrate through 2000‐A Al films at 250 °C and 24 h vacuum anneal. Schottky barrier height φB increases approximately 0.10 eV as a result of annealing at 250 °C. However, φB remains constant between 250 and 450 °C.

Low‐temperature interdiffusion between aluminum thin films and GaAs

The structure and thermal stability of bimetallic Au‐Ta films has been studied by x‐ray diffraction, electrical resistivity, and by microscopy. Annealing above 450 °C forms a TaAu compound. The growth of the TaAu layer at the Au–Ta interface follows a parabolic rate law. A low‐temperature depletion of gold at tantalum grain boundaries occurs below 350 °C with an activation energy of 0.41 eV. Grain growth occurs with an activation energy of 0.50–0.55 eV for gold and 0.40–0.50 eV for tantalum. Thermal stresses of the order of 1.0×109 dyn/cm2 exist in the sputtered films.

H. M. Day

Papers

Low‐temperature interdiffusion between aluminum thin films and GaAs

Structure and thermal stability of sputtered Au–Ta films

Reactions Between the Ta‐Pt‐Ta‐Au Metallization and PtSi Ohmic Contacts