Transferred electron effect

The transfer of conduction electrons from a region of high mobility energy to a region of low mobility is called transferred electron effect. Here low mobility target region should be a high energy satellite valley. The various materials which exhibit this effect are GaAs, InP, CdTe, ZnSe, and GaAsP. In some other materials, a proper change in band structure facilitates transfer electron effect. Classic example is that of InAs, where application of pressure facilitates transfer electron effect. To occur transfer electron effect phenomenon, the lattice temperature must be very low and in the absence of bias electric field, most of the electrons should be in lower conduction band. These electrons which occupy lower conduction band should have high mobility, small effective mass and low density of states. The other electrons which remain in upper satellite valleys should possess low mobility, large effective mass and high density of states. The energy gap between two valleys should be very small to achieve transfer of electrons into the upper valleys before the start of avalanche breakdown. Transferred electron devices are microwave devices and are extensively used in RADAR, microwave test instruments and intrusion alarms. Gunn diodes are microwave devices which operate by the transferred electron mechanism.