| Abstract [eng] |
Summary STUDY OF ANNEAL – INDUCED RADIATION DEFECT TRANSFORMATIONS IN Si pin PARTICLE SENSORS Augustas Baliukonis Silicon is an extremely useful material as it has relatively good semiconducting parameters and is also abundant. The doping process of silicon has also been mastered, as a result of doping, silicons electrical characteristics can be manipulated much more easily than without doping. Such manipulation of electrical characteristics gave rise to some crucial electronic components of today, such as a transistor or a diode. One way a diode can be used is as a sensor. In fact, diode – based sensors are used in medicine or high – energy physics experiments. One phenomenon that is important for such sensors is the fact that over time they tend to degrade and become increasingly less reliable – such degraded sensors no longer provide a response signal that accurately shows the irradiation intensity. Most commonly, the reason for such degradation is the accumulation of radiational defects, caused by high – energy particles. However, a possible way to, at least partially, recover such sensors would be to anneal them due to a higher temperature possibly reducing defect concentration. One method to experimentally see the degradation is by observing an increasing leakage current in the current – voltage dependency of a diode. However, this method is simple and simplicity has a cost – it only shows that the sensor has degraded, but does not show what exact defects caused this degradation. That is where more complex methods, such as PIS (photoionization spectroscopy) or DLTS (deep level transient spectroscopy) come into play, as they allow one to identify these defects and their parameters. In this particular work, silicon diodes named “SFH2700”, made by the German company “OSRAM” are tested with the aim of this work being finding out about radiation defects, their parameters and how these defects, along with their parameters, change after annealing in such diodes. The diodes were irradiated with electrons, at doses of and 1,9 kGy, 5,4 kGy, 12,4 kGy and 20 kGy. After the measurements of each sample with all of the mentioned techniques, the samples were annealed at 80°C, 200°C and at 400°C. Firstly, current – voltage measurements were carried out due to their simplicity and ability to provide basic, yet fundamental information. Next, PIS and DLTS measurements were carried out to find out about specific defects and their parameters. Current – voltage measurements showed increasing leakage current with respect to accumulated dose. With respect to annealing temperature, a slight decrease in reverse current was measured after annealing, but not even close to being similar to the reverse current of a pristine sample. PIS and DLTS techniques allowed identifying defects and their parameters, however, to different extents. PIS measurements, when modelled according to Kopylov – Pikhtin model, showed two defects with their activation energies, while DLTS measurements showed much more defects with their activation energies, most of the defects acting as majority carrier traps and one of the defects acting as a minority carrier trap. After annealing, all of the traps showed a decrease in concentration. |
