Effect of bias conditions on transient anode current for quasi-double-sided silicon drift detector with high energy resolution

Abstract

Silicon drift detectors (SDDs) are widely applied for x-ray detection due to their remarkable energy resolution. The main contribution to energy resolution is the electrical noise of measurement system. In addition, other factors, including imperfect charge collection and ballistic deficit, can deteriorate the energy resolution. Those factors are closely related to the bias conditions of the device. However, the effect of bias conditions on device energy resolution has rarely been reported, primarily because the applied bias of classical SDDs is limited by twice the depletion voltage and little attention is focused on bias conditions. In order to enhance the flexibility of bias conditions and investigate the effect of bias conditions on energy resolution, we proposed a novel quasi-double-sided silicon drift detector (QD-SDD) with a drift ring structure designed on the back side. Device simulations of SDD and QD-SDD under different bias conditions were performed to obtain the transient current response of the anode. It was found that the QD-SDD has greater flexibility in bias conditions, and then better electron collection efficiency and shorter electron collection time can be realized at higher bias voltage (> 200 V). Finally, the fabricated QD-SDD was characterized using a 55Fe radioactive source. The experiment results showed that the energy resolution of QD-SDD varies with different bias conditions. The optimal energy resolution is 170 eV under the optimized bias conditions.