Papers by Author: Zheng Li

Abstract: A theoretical model for radiation effect in a metal-ferroelectric-semiconductor (MFS) field-effect transistor was proposed by considering the fixed charges (Q_fx) and interface charges (Q_it) induced by ionizing radiation. In this model, the energy band-bending and surface charge in Si at a given gate bias were calculated systematically as a function of fixed charges (Q_fx) and interface charges (Q_it). The drain-source current (I_D) was derived in an exact form without any approximation. All modeling done in this work was generalized to both n and p type Si substrates with an easy sign of the Fermi level potential in the formalism. The derived results demonstrate that the symmetry of polarization versus gate voltage curve of the MFS structure degrades when Q_fx and Q_it increase, which can explain the imprint behavior successfully. Additionally, the residual polarization in the ferroelectric field-effect transistor decreases with increasing Q_fx and Q_it, which can account for the polarization reduction. As expected, the calculated transfer characteristic of the ferroelectric FET shows that the subthreshold voltage is significantly affected by Q_fx and Q_it. This investigation may provide some useful insights for the space applications of ferroelectric FET’s.

Abstract: The objective of this paper is to give an overview on how silicon particle detector would survive operational in extremely harsh radiation environment after luminosity upgrade of the CERN LHC (Large Hadron Collider). The Super-LHC would result in an integrated fluence 1×1016 p/cm2 and that is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies. The Czochralski silicon (Cz-Si) has intrinsically high oxygen concentration. Therefore Cz-Si is considered as a promising material for the tracking systems in future very high luminosity colliders. The fabrication process issues of Cz-Si are discussed and the formation of thermal donors is especially emphasized. N+/p-/p+ and p+/n-/n+ detectors have been processed on magnetic Czochralski (MCz-Si) wafers. We show measurement data of AC-coupled strip detectors and single pad detectors as well as experimental results of intentional TD doping. Data of spatial homogeneity of electrical properties, full depletion voltage and leakage current, is shown and n and p-type devices are compared. Our results show that it is possible to manufacture high quality n+/p-/p+ and p+/n-/n+ particle detectors from high resistivity Czochralski silicon.

Abstract: Segmented silicon detectors are widely used in modern high-energy physics (HEP) experiments due to their excellent spatial resolution and well-established manufacturing technology. However, in such experiments the detectors are exposed to high fluences of particle radiation, which causes irreversible crystallographic defects in the silicon material. Since 1990’s, considerable amount of research has gone into improving the radiation hardness of silicon detectors. One very promising approach is to use magnetic Czochralski silicon (MCz-Si) that has been found to be more radiation hard against charged hadrons than traditional Float Zone silicon material (Fz-Si) used in the current HEP applications. Other approaches include operating the devices at cryogenic temperatures and designing special detector structures such as p-type detectors or semi-3D detectors. In order to demonstrate that the developed technologies are suitable for the HEP experiments, it is necessary to extensively characterize the potentially radiation hard detectors. We have an excellent instrument for this, the Cryogenic Transient Current Technique (C-TCT) measurement setup, which is an effective research tool for studying heavily irradiated silicon detectors. With the C-TCT setup it is possible to extract the full depletion voltage, effective trapping time, electric field distribution and the sign of the space charge in the silicon bulk in the temperature range of 45-300 K. This article