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The paper studies the characteristics of Gunn diodes based on graded-gap GaInPAs semiconductor. Gunn diodes are active elements for generating electromagnetic waves in the millimeter and submillimeter ranges. Nowadays, providing modern equipment with active sources of the subterahertz range is an urgent task. It can be implemented by increasing Gunn diodes power and cutoff frequencies of generation. One of the means to increase the cutoff frequency of Gunn diodes is the use of graded-gap semiconductors. The dependence on the coordinate of many parameters of a graded-gap semiconductor affects the processes that occur in the Gunn diode based on the graded-gap semiconductor. Therefore, it is very important to optimize the diode structure by both the doping level and varying the fraction parts of the graded-gap alloy. The paper presents the results of modeling the operation of Gunn diodes with an active zone length of 1 μm based on graded-gap GaPAs -GaInAs alloy at different lengths of the graded-gap layer, different fraction parts of In and P and different electron densities in the active zone. The power spectra of self-oscillations (in the absence of a resonator) of Gunn diodes are obtained, the analysis of physical processes is performed, the optimal lengths of the graded-gap semiconductor layer and optimal mole fractions of In and P are found to obtain the highest power and oscillation frequency. For diodes with an electron density in the active zone of 6×10 16 cm -3 , Ga0.67P0.33As -Ga0.5In0.5As has the greatest oscillation power at the layer length of the graded-gap compound equal to 0.2 m. This diode provides an RF power of 11.28 mW at 102.5 GHz for the fundamental harmonic and 49 W (307.5 GHz) for the third harmonic.

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Subject and Purpose. The InN Gunn diode is known as the device capable of generating powerful oscillations atfrequencies above 300 GHz. A possible way for increasing both the microwave power and the cutoff frequency of the Gunn diode is to employ graded-gap semiconductors. The subject of this research is the process for generating electrical oscillations in InN and graded-gap GaInN Gunn diodes that involve resistive contacts at the cathode and the anode, and possess a 1-μm long active region. The research is aimed at suggesting an optimized structure for the graded-gap GaInN diode to obtain a maximum microwave power and maximum frequency of the oscillations, while consuming the lowest possible amount of DC power. Methods and Methodology. А hydrodynamic simulation has been performed of transport of electrons in graded-gap semiconductors, and an integro-differential equation analyzed concerning voltage drop across elements of the related RLC circuit. Results.The power spectra of oscillations have been analyzed for a variety of parameters of both the Gunn diode and the RLC circuit. The frequency dependences of the oscillatory power, characteristic of different electron concentrations, provide evidence for the possibility of obtaining considerable microwave powers at frequencies above 300 GHz through the use of graded-gap GaInN diodes. Conclusion. The results that have been obtained clearly confirm the expected practicality of using a graded GaInN layer in the InN diode for increasing the power of microwave oscillations, reducing the necessary level of the DC power, and restraining the dependence of the output characteristics on the electron density. The highest power of oscillations has been demonstrated by the InN diode with a 0.1 µm long graded-gap layer of GaInN. Meanwhile, the oscillation frequency generated in that diode is somewhat lower than in the InN diode. A compromise between the values of generated power and the oscillation frequency has been reached in the diode with a graded-gap GaInN layer of 0.9 µm in length. In addition, the latter structure requires the lowest level of DC power for effectuating microwave generation at the higher feasible frequencies.

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