D-band (110-170 GHz) InP gunn devices

This paper reports on the development of InP Gunn sources for operation in the D-band (110-170 GHz). 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 μm structure with a uniform n doping of 2.5 × 10¹⁶ cm^-3. The CW RF output power was 33 mW. A 1 μm graded structure with an n doping increasing linearly from 7.5 × 10¹⁵ to 2.0 × 10¹⁶ cm^-3 has resulted in 20 mW at 120 GHz and 10 mW 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 InGaAs cap layers. An etch-stop layer allows low-profile mesas (2-3 μm) 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 μm Gunn device operating at W-band frequencies were used to estimate appropriate InP material parameters.