An alloy of Au, Ge and Ni has been shown to produce uniform linear electrical contacts to GaAs over a resistivity range useful for bulk effect devices. Batch fabrication of devices with contacts of controlled size and shape is readily accomplished by evaporating the contact material through masks onto the semiconductor surface. An eutectic alloy of Au and Ge also produces a linear contact but tends to produce nonuniform films. The preparation of the contact materials, surface treatment of the GaAs, and device fabrication procedures are described.

Metal-semiconductor contacts for GaAs bulk effect devices

A computer simulation of a GaAs Gunn diode in a parallel resonant circuit has been made to determine the optimum device and circuit parameters. The maximum dc to RF efficiency, 5 to 8 percent, is obtained when the product of doping and length is between 1012and 2 × 1012cm-2, the product of frequency and length is 107cm/s, and the bias voltage divided by length is 8000 V/cm for a load resistance of 30 R_{0} where R 0 is the low-voltage resistance of the diode. The product of output power and load resistance varies with frequency f as C f^{2} where C is 12,000 watt-ohm-GHz2for a load resistance of 50 R_{0} . The frequency can be varied over an octave tuning range by the resonant circuit.

Theoretical study of a Gunn diode in a resonant circuit

Noise spectra of read diode and Gunn oscillators

An in situ Ohmic‐contact‐formation technique for n‐ and p‐GaAs of any resistivity by molecular beam epitaxy was described. The measured specific contact resistances lie between low‐10−6 Ω cm2 and mid‐10−5 Ω cm2. The contacts were Ohmic for currents in excess of 250 mA tested in both forward and reverse directions. Furthermore, the contact metallization was optically smooth as no sintering or alloying process was needed. Excellent uniformity of electrical quality of the Ohmic contacts on the same sample was obtained.

In situ Ohmic‐contact formation to n‐ and p‐GaAs by molecular beam epitaxy

By measuring the steady‐state potential distribution in n—GaAs samples with ohmic contacts, very high electric fields have been found near the anode contacts. In samples with n · L (carrier concentration × sample length) products greater than 1012 cm‐2, switching from the Gunn mode to a high current, lower (constant) voltage state takes place along with the appearance of a high field at the anode. In samples with n · L products less than 1012 cm‐2 the buildup of the high field is accompanied by a sudden increase in current. These high currents are due to carrier generation in a narrow region near the anode.

CARRIER GENERATION AND SWITCHING PHENOMENA IN n—GaAs DEVICES

Recent results with epitaxial GaAs Gunn effect oscillators

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Recent results with epitaxial GaAs Gunn effect oscillators