Generation lifetime analysis of p-n junction X-ray detector

Operation lifetime of the X-ray detector is the major factor that defines cost of detector or the actual operation cost of the detector. The purpose of this paper is to study the possibility of operation lifetime extension of the silicon x-ray detector. The study of the device's carrier generation lifetime before and after device exposed to the X-ray for 4 and 150 second at 40, 55 as well as 70 keV were conducted in this paper. The 1 mm² p-n junctions were fabricated by boron implantation process into phosphorus doped silicon wafer. A commercial x-ray source for dentist was used to generate x-ray in these experiments. The carrier generation lifetime was calculated from current-voltage (I-V) and capacitance-voltage (C-V) characteristics. The results show that the carrier generation lifetime increased after 4 second of x-ray irradiation at all three energy conditions but decreased back close to the original value after continue exposed devices for another 150 second. However, the lowest point of the generation lifetime after 4 second of x-ray irradiation is depending on the level of energy used. The results also presented that the defects that caused by x-ray irradiation are manageable.

I. INTRODUCTION

The X-ray detector is widely use for medical analysis. However, its utilization has limit not only by safety concerns but also by its cost. The X-ray detector itself is expensive, which results high cost of operation. The cost of operation can be reduced by extending the detector operation lifetime, which will increases its cost benefit for longer operation and increase opportunities for people to access to this machine. In this paper, we concentrate on study the possibility to extend X-ray detector operation lifetime by analyst the carrier generation lifetime of p-n junction before and after exposed to the X-ray at different conditions of energy and time. This parameter is used as a monitoring method for the device degradation since it can be refer to amount of defects or lattice disorders in the p-n junction effective area which lead to a breakdown condition of the device.