Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier – To compound semiconductor
Patent
1995-11-05
1997-09-09
Crane, Sara W.
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
To compound semiconductor
257623, 257655, 257 12, H01L 2947
Patent
active
056659997
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Rectifying, majority carrier-predominated metal-semiconductor diodes (so-called Schottky diodes) are used in the form of individual components or in the form of monolithically integrated circuits (so-called MMICs) for mixers and detectors in sensor, communications and radar systems used at extremely high frequencies. Metal-semiconductor diodes from the III/V material gallium arsenide (GaAs) are used for this purpose almost exclusively due to the fact that their electronic properties are more favorable for these applications. Furthermore, the resistive (so-called semi-insulating) GaAs substrate is favorable for the integration technique in the high-frequency range for manufacturing technical reasons, and it is therefore preferably employed.
BACKGROUND OF THE INVENTION
The highest sensitivities ever have been reached and maximum frequencies up into the terahertz range are attained with such diodes. The relatively high cutoff voltage of the diodes in the forward direction, which is typically in the range of 0.7 V to 0.8 V due to electronic surface states in the GaAs, is a disadvantage of these components. To reach sufficient performance capacity for mixer applications in terms of conversion loss, pumping capacity, sensitivity and noise behavior, such diodes are therefore operated with bias voltages (e.g., S. A. Maas: Microwave Mixers, 2nd edition, Artec House, Boston, 1993).
However, operation with a bias voltage leads to disturbances known as Townsend current hum. On the other hand, operation without bias voltage requires a high pumping capacity of the local oscillator (LO) to reach a low conversion loss.
It has been known from theoretical calculations from U. V. Bhapkar, T. A. Brennan and R. J. Mattauch: InGaAs Schottky Barrier Mixer Diodes for Minimum Conversion Loss and Low LO Power Requirements at Terahertz Frequencies, Proceedings of the 2nd international Symposium on Space Terahertz Technology, Feb. 1991, pp. 371-388, that a marked reduction in the necessary LO power for pumping the mixer diode can be expected from Schottky diodes with reduced electron release barriers at InGaAs depletion zone layers compared with GaAs depletion zone layers at comparable conversion losses. In addition, structures consisting of InGaAs layers with constant In content (20% or 30%) and experimental results were already mentioned in the above-mentioned publication. To obtain acceptable depletion zone lengths, layer thicknesses between 80 nm and 150 nm were prepared. However, these thicknesses are far greater than the corresponding critical layer thicknesses, so that the regions are already partially relaxed. Such structures contain a large number of dislocation lines and crystal defects, which exert a highly unfavorable effect on the electronic behavior of the diode as well as on the reliability and the quality of the component.
Even though it is possible, in principle, to prepare non-relaxed InGaAs layers on GaAs with high In content by drastically reducing the InGaAs layer thickness to values markedly below the critical layer thickness (e.g., below a thickness of less than 5 nm for an In concentration of 30%), this leads to an appreciable reduction of the electron barrier, because the conduction band jump between InGaAs and GaAs is very close to the Schottky contact and the edge of the conduction band of the GaAs material represents the effective barrier height for the current transport. Such a component consequently behaves like a diode with a GaAs depletion zone layer.
It has been known from K. Kajiyama, Y. Mizushima, and S. Sakata: Schottky Barrier Height of n-InxGal-xAs Diodes, Applied Physics Letters, Vol. 23, No. 8, pp. 458-459, 1973, that the electron release barrier in InGaAs material continuously decreases with increasing In content, beginning from pure GaAs material, and there is no barrier any more for pure InAs material. It has been well known that the lattice constant increases nearly linearly with increasing In content, which leads to a corresponding mismatch between InGaAs and GaA
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Crane Sara W.
Daimler - Benz AG
Hardy David B.
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