Speaker
Prof.
Juozas Vaitkus
(Vilnius University)
Description
Simultaneous measurements of the characteristics of photoconductivity transients, TOF, SCD (TCT) and SCLC by using various regimes of the surface and bulk excitation as well as current transient differential and integral registration regimes have been performed to clarify the electric field and neutron fluence dependent variations of carrier recombination and drift parameters in pad-detectors fabricated on MCZ Si. Significant changes of carrier drift time and of recombination with increase of fluence from 1012 to 1016 n/cm2 of the reactor neutrons have been obtained. However, carrier recombination lifetime is independent of the applied electric field at fixed irradiation fluence. It has been unveiled that current transients are determined by diffusion of light induced carrier domain at lowest values of applied voltage while these transients evolve via SCLC and SMD regimes to TOF transient with increase of electric field strength for low and moderate irradiation fluences. Changes of current transients due to variation of the carrier drift regimes are always observed within time scale of excess carrier density decay controlled by microwave probed photoconductivity transients. Peculiarities of extraction of material parameters at different regimes are discussed. Enhancement of excess carrier density with intensity of excitation tends to dominance of the diffusion of carrier domain and of the SCLC regimes at applied voltages up to full depletion of pin diode for fluences of <1015 n/cm2. Crucial shortening of carrier diffusion length at fluences > 1015 n/cm2 determines current transients which weakly depend on applied field.
Analyze of the linear dependence of free carrier lifetime on fluence performed by modelling of clusters using the density functional theory. The calculated decrease of bandgap at the ring shape clusters (V6) demonstrate the importance of the local field for both carriers drift to the cluster and it causes the near to the linear decrease of the lifetime dependence on hadron fluence.
Author
Prof.
Juozas Vaitkus
(Vilnius University)
Co-authors
Mr
Aurimas Uleckas
(Vilnius University)
Dr
Ernestas Žąsinas
(Vilnius University)
Dr
Eugenijus Gaubas
(Vilnius University)
Mr
Tomas Čeponis
(Vilnius University)
