Investigation of Deep-Level Effects on Dark Current of Proton Irradiated Silicon PIN Photodiodes

ARIEL PABLO CÉDOLA; MARCELO ANGEL CAPPELLETTI; EITEL LEOPOLDO PELTZER Y BLANCÁ

Smolenice, Eslovaquia

Conferencia; ASDAM 08 (International Conference on Advanced Semiconductor Devices and Microsystems); 2008

IEEE (Institute of Electrical and Electronics Engineers)

Damage induced by proton irradiation on silicon PIN photodiodes produces a linear increment of dark current with particle fluence. This effect results of great utility when devices are used as radiation detectors. However, it represents an undesirable effect in optoelectronic space systems. In previous work, authors have studied this dependence of dark current with radiation through numerical simulations. A simple linear analytical model has been proposed for dark current based on obtained results [1] and an iterative method has been established for determination of the optimum intrinsic Si layer length that minimize radiation effects on PIN photodiodes for space applications [2]. In the present work, and following with this field of research, the theoretical study of irradiated PIN photodiodes is enhanced by including different kinds of deep-traps in the computer simulation routines. Deep-levels can be attributed to atoms of impurities introduced during the manufacturing of devices. These levels are centers of carriers recombination/generation and the most effective of them are those with energies close to the middle of the bandgap. Four different kinds of deep-traps were considered in simulations: 1 energy level at the middle of Si bandgap, 2 levels (Au), 3 levels (Fe) and 4 levels (Cd) (Fig.1) [3]. Trap densities of 1014 cm-3 were used in all cases. Silicon p+/n-/n+ structures with total lengths (LT) of 30 µm and 50 µm were simulated. Five intrinsic layer lengths (LI) were assumed for each total device length: LI=(0.7)LT, LI=(0.75)LT, LI=(0.8)LT, LI=(0.85)LT and LI=(0.9)LT. In turn, these ten devices were analyzed considering each one of the four proposed deep-trap models. The larger the device intrinsic layer, the greater the dark current increment with proton irradiation fluence. The slope of dark current linear evolution with absorbed radiation is different for each trap model (Fig.2). This slope depends on the number of introduced energy levels by the impurities, their position in bandgap and their type, donor or acceptor. It can be observed that curve for the trap model with three energy levels falls below the curve corresponding to the single level. Physics involved in these processes are analyzed in detail in the full paper.