Combined doping and geometry effects on transferred-electron bulk instabilities

The behavior of transferred-electron bulk negative differential conductivity devices with nonuniform geometries and various doping profiles is analyzed. Computer solutions were obtained for appropriate transport equations generalized by a scheme to simulate arbitrary areal variation. The solutions show that the effects of doping and geometrical nonuniformities on domain dynamics are similar. The product of doping and transverse area plays an important role in determining the space-charge properties. An important practical implication of the above result is demonstrated by a scheme for device design using combinations of geometrical and doping nonuniformities to achieve a desired control characteristic. Various equivalent device configurations yielding a linear frequency-voltage characteristic over a wide frequency range are proposed.