Theoretical and practical investigation of the thermal generation in gate controlled diodes

The different components of thermal generation in a gate controlled diode are studied theoretically and experimentally. Expressions for the generation current in the space charge layer, the diffusion current from the quasi-neutral bulk and the surface generation current are derived for a gated-diode. The width of the generation zone within the space charge layer is calculated as a function of the energy level of the trap and the diode reverse voltage. This leads to a characteristic of the leakage current as a function of the space charge layer width. It is pointed out that the diffusion current can influence the leakage current and cannot be neglected in structures with a low dark current. In the second part the gate controlled diode is used to characterize the thermal generation in structures with a homogeneous and low dark current. A generation lifetime of 5.5 msec and a surface generation velocity at a depleted surface of 1.5 cm/sec is derived. The generation lifetime is found to be constant as a function of depth into the substrate. A considerable diffusion current is measured which is comparable to the generation current in the space charge layer.