Abstract-Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators first at -band (110-170 GHz) and then at -band (75-110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above -band and operation in a second-harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter-wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared.

This paper reports on the development of InP Gunn sources for operation in the D-band (li0-170GHz). n+-n-n + structures with flat doping as well as graded doping profiles have been considered. Oscillations were obtained at 108.3 GHz from a 1 #m structure with a uniform n doping of 2.5 x 1016cm-3. The CW RF output power was 33 roW. A 1 #m graded structure with an n doping increasing linearly from 7.5 x 10 ~5 to 2.0 x 10~6cm-3 has resulted in 20roW at 120GHz and 10roW at 136 GHz. These results are believed to correspond to a fundamental mode operation and represent the state-of-the-art performance from InP Gunn devices at these frequencies. This improvement in performance is attributed in part to a processing technique based on the use of etch-stop layers and lnGaAs cap layers. An etch-stop layer allows low-profile mesas (2-3/~m) and InGaAs cap layers help reduce the contact resistance, thus minimizing series resistances in the device. In addition, a physical model based on the Monte Carlo method was developed to aid in the design of structures for high frequency operation. Experimental results obtained from a 1.7#m Gunn device operating at W-band frequencies were used to estimate appropriate InP material parameters.

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