SHORT COMMUNICATION Design and Fabrication of 35 GHz GaAs Gunn Diodes

The paper describes design and fabrication of GaAs I()(} mW Gunn diodes for operation at-35 GHz. As the devices have low efficiency, a large amount of input power is dissipated as heat, resulting in temperature rise in the device during operation beyond tolerable limits. Heat from these devices can be removed quickly and efficiently by using gold as integral heat sink (IHS). Further, the temperature of the device can be controlled by monitoring device area. Calculations for heat flow and expected efficiency have been done. Required Gunn structure has been grown by molecular beam epitaxy technique. The devices have been fahricated by IHS-IBR (integral bonding ribbon) technique. From the devices developed, 100 mW of output has been achieved in the frequency range 33-38 GHz with an efficiency of 3-4 per cent. semiconductors which have a multivalley structure in their conduction hand. Gallium arsenidc is the main rcpresentative of this class. When a thin sample of this material is hiased, the current increases linearly with hiasing voltage following Ohm's law. As the hias voltage increases heyond the threshold voltage, the current starts decreasing giving rise to negative differential resistance; and current oscillations in the circuit are oh served. The decrease in current is found to he associated with the transfer of elt,",llons from the high mohility, low effective electron mass central valley to low mohility, high effective mass satellite valley. Because of this excitation, the fast moving electrons get slowed down and form a high field domain (comprising accumulation/depletion of electrons) which moves with saturated velocity under the influence of electric field. The high field domain normally nucleates at the cathodc end and after traversing the whole length of the sample, annihilates at the anode end, giving a current spike. A new domain is again nucleated and the cycle is repeated. I