Recent developments in transferred electron devices

After an introductory description of the foundations the review outlines recent advances in the understanding and technology of transferred electron devices. Development of numerical techniques for calculating averages of the electron momentum distribution and its response rate to time varying electric fields have clarified limitations of device performance. High pulse powers are generated by overlength relaxation devices but the low power CW transit time oscillators have had the greatest application. Advances in material technology are removing some limitations of early diodes. Considerable interest is being shown in the amplification properties of supercritical transferred electron devices and in the potentialities of indium phosphide as a transferred electron material.