An Analytical Model of SiGe Heterojunction Bipolar Transistors on SOI Substrate for Large Current Situations

The large current effect of silicon germanium heterojunction bipolar transistors fabricated on thin silicon-on-insulator is included in the model.As the current is two-dimensional,the injection for large current is vertical plus horizontal and is quite different from that of the bulk device.Critical parameters modeling the large current,such as the collector injection width,the hole density and the corresponding potential in the injection region,are discussed,and the influence to the transit time is also analyzed.

Neutron radiation effect on 4H-SiC MESFETs and SBDs

4H-SiC metal Schottky field effect transistors（MESFETs） and Schottky barrier diodes（SBDs） were irradiated at room temperature with 1 MeV neutrons.The highest neutron flux and gamma-ray total dose were 1×1015 n/cm2 and 3.3 Mrad（Si）,respectively.After a neutron flux of 1×1013 n/cm2,the current characteristics of the MES-FET had only slightly changed,and the Schottky contacts of the gate contacts and the Ni,Ti/4H-SiC SBDs showed no obvious degradation.To further increase the neutron flux,the drain current of the SiC MESFET decreased and the threshold voltage increased.φB of the Schottky gate contact decreased when the neutron flux was more than or equal to 2.5×1014 n/cm2.SiC Schottky interface damage and radiation defects in the bulk material are mainly mechanisms for performance degradation of the experiment devices,and a high doping concentration of the active region will improve the neutron radiation tolerance.

Directed Proxy Signature in the Standard Model

A directed signature is a type of signature with restricted verification ability.Directed signatures allow only a designated verifier to check the validity of the signature issued to him,and at the time of trouble or if necessary,any third party can verify the signature with the help of the signer or the designated verifier.Directed signature schemes are widely used in situations where the receiver's privacy should be protected.Proxy signatures allow an entity to delegate its signing capability to another entity in such a way that the latter can sign message on behalf of the former when the former is not available.Proxy signature schemes have found numerous practical applications such as distributed systems and mobile agent applications.In this paper,we firstly define the notion of the directed proxy signature by combining the proxy signature and directed signature.Then,we formalize its security model and present a concrete scheme in the standard model.Finally,we use the techniques from provable security to show that the proposed scheme is unforgeable under the gap Diffie-Hellman assumption,and invisible under the decisional Diffie-Hellman assumption.