ON THE DESIGN OF DOPING CONCENTRATION PROFILES FOR GAAS TRANSFERRED-ELECTRON DEVICE LAYERS

The doping concentration profile of the GaAs region has a significant effect on the d.c.-microwave conversion efficiency of a transferred-electron device operating as a source of microwave power. Transferred-electron device layers are commonly grown so that the doping concentration profile of the active region is predominantly uniform. However, for higher device efficiency the doping concentration should be graded, gradually increasing from the cathode to the anode. Also the operating temperatures across the active region should be minimized by ensuring that the length of the highly-doped GaAs region between the active region and the heat sink is as short as possible. In this paper, the design of the active region doping concentration profile for high-efficiency GaAs transferred-electron devices is discussed. The measured power output of a microwave oscillator, using devices with uniform and graded doping concentration profiles, is given. The d.c.-microwave conversion efficiency of the devices with graded doping concentration profiles is shown to be significantly superior. Furthermore, to calculate accurately the operating temperatures across the active region, novel analytic expressions for the temperature profile are given as a function of the geometry and material composition of the device and the d.c. input power.