Graphical optimization of the doping profile of transit-time devices

The doping profile of transit-time avalanche diodes has evolved from a compromise of technological convenience and the original structure proposed by Read [1]. A technique by which the doping profile my be quickly optimized is described, and it is shown that a four-layer p-n-p-n structure should give the highest efficiency for a transit-time diode. This technique, which my be generalized to other types of device, predicts the maximum power density available from the optimum structure. For a Read-type diode, operating in X band, this is in the region of 40 kW/cm²at an efficiency of around 30 percent. Higher efficiencies are attainable at the expense of output power.