The structure and properties of metal-semiconductor interfaces

A correlation between the interface chemistry and the electrical properties of evaporated tungsten Schottky‐barrier contacts to GaAs is made by using data obtained by x‐ray photoemission spectroscopy (XPS), current‐voltage (I‐V), and capacitance‐voltage (C‐V) techniques. A chemical reaction and associated nonabruptness was observed both at ideal (initial clean surface) and at practical (initial native‐oxide covered surface) W‐GaAs interfaces during Schottky‐barrier formation at room temperature. The XPS measured W Schottky‐barrier height for both types of interface is 0.9 eV. I‐V and C‐V measurements were made for a sequence of anneal temperatures up to 650 °C; changes in the contact electrical properties occurred at each temperature. The reactive W contacts are compared to relatively nonreactive Au contacts to GaAs similarly prepared and characterized. The I‐V and C‐V properties of Schottky‐barrier contacts are found to be strongly influenced by the chemistry associated with interface formation.

Interface chemistry and electrical properties of tungsten Schottky‐barrier contacts to GaAs

The Ti metal interdiffusion of Ti/Pt/Au gate metal stacks in 0.15-/spl mu/m GaAs PHEMTs subjected to high-temperature accelerated lifetest has been physically identified using scanning transmission electron microscopy. Further energy dispersive analysis with X-ray (EDX) analysis confirms the Ti diffusion into the AlGaAs Schottky barrier layer and the decrease of Schottky barrier height suggests the Ti-AlGaAs intermetallic formation, which is consistent with previous Rutherford backscattering spectroscopy/X-ray photoelectron spectroscopy studies. The Ti metal interdiffusion reduces the separation of the gate metal and InGaAs channel, thus leading to a slight Gm increase, positive shift in pinchoff voltage, and S21 increase during the preliminary portion of the lifetest. Accordingly, the Ti interdiffusion effect implies that the lifetime of GaAs PHEMTs subjected to high-temperature accelerated lifetest could be dependent upon the initial thickness of the Schottky layer underneath the gate metal.

Physical identification of gate metal interdiffusion in GaAs PHEMTs

This work reports and critically reviews failure mechanisms induced by metal-GaAs interaction and contact degradation in low and medium power GaAs MESFETs in the framework of a comprehensive reliability evaluation test plan, performed mainly on commercially purchased devices manufactured by different technologies. The results show that, at least as regards contact degradation phenomena, these technologies have reached sufficient maturity, and significant reliability levels have been achieved even for the most severe application and environments. Devices coming from some suppliers still suffer from reliability problems. such as ‘sinking’ of Au-based gate metallization into the active channel. Al electromigration, Al/GaAs interdiffusion enhanced by high contacts electromigration, surface metal migration and short circuiting of closely spaced electrodes on GaAs with a non-suitable surface preparation and/or passivation. All these failure mechanisms have been identified by means of suitable microanalytical techniques, correlated with device electrical degradation and thoroughly discussed in this paper by comparison with results previously reported in the technical literature.

Metal–GaAs interaction and contact degradation in microwave MESFETs

Grain boundary and interdiffusion studies in compound semiconductor thin films and devices utilizing Auger electron spectroscopy and secondary ion mass spectroscopy

Au–W(Ti)/n‐GaAs diodes were constructed for the purpose of examining the thermal stability of the metal–GaAs interface and the integrity of the W(Ti) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(Io), determined by measurement of the zero voltage current intercept, Io, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(Io) up to 500°C. Above 500°C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation, and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished.

Interdiffusion and Schottky‐barrier‐height variations in Au–W(Ti)/n‐GaAs contacts

Epitaxial growth of (100) GaAlAs and Al was achieved on (100) n‐GaAs substrates using vacuum deposition in an ultrahigh vacuum system. In situ Auger electron analysis, microspot Auger electrospectroscopy, LEED, and reflection electron diffraction was used to characterize the films. Regions of GaAlAs and Al were identified. Electrical measurements indicated the presence of a stable Schottky barrier with a barrier height of 0.76 eV.

Epitaxial growth of Al/GaAlAs films on (100) GaAs by hot vacuum deposition

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Interdiffusion and Schottky‐barrier‐height variations in Au–W(Ti)/n‐GaAs contacts

Epitaxial growth of Al/GaAlAs films on (100) GaAs by hot vacuum deposition