Hot Carrier Studies on Heterostructure Silicon Germanium P-Channel Metal Oxide Semiconductor Field Effect Transistor

This study examines the susceptibility of hot carrier effects on various Heterostructures Silicon Germanium P-Channel Metal Oxide Semiconductor Field Effect Transistor (SiGe PMOSFET) such as Strained SiGe Channel and Strained SiGe Source/Drain PMOSFET. The results were compared with Si Channel PMOSFET. The hot carrier effect of these structures was investigated in the aspect of material, structural and mobility via impact ionization. Simulations were performed with ATLAS/BLAZE 2D to design the device structures and to simulate the hot carrier effects indicated by substrate and gate current. The SiGe heterostructure PMOSFETs have higher hot carrier effects as verified by substrate current with an increase of 131% for Strained SiGe Channel PMOSFET and 199% for Strained SiGe Source and Drain PMOSFET with 25% Ge fraction respectively as compare to the Si PMOSFET. The increase of hot carrier effects in SiGe structure is due to higher impact ionization rate approximately an order of magnitude in SiGe as compared to Si. The incorporation of Si-cap in the SiGe heterostructure enhanced the suppression of hot carrier injected into the gate. However the buried layer of Strained SiGe channel PMOSFET suppresses the impact ionization rate to a certain level of thickness. Beyond that impact ionization increases with the Ge content as verified by substrate current. On the other hand the increase of Ge content suppressed further the hot carrier injection into the gate due to higher valence band energy between the SiGe channel and the Si-cap. As a thicker layer of p+SiGe in the drain region is fabricated in the Strained SiGe Source and Drain PMOSFET result shows an enhancement in the hot carrier effect. This is caused by a higher impact ionization rate in SiGe and also most area of impact ionization is covered as the thickness of SiGe layer is increased. In the aspect of mobility, the high mobility SiGe channel PMOSFET enhanced further the hot carrier effects through the enhancement of current drive whereas hot carrier effects decreases in the Strained SiGe Source and Drain PMOSFET despite setting a higher low field mobility in the p+ SiGe source and drain region. In fact the current drive in Strained SiGe Source and Drain PMOSFET is lower than Si Channel PMOSFET due to the valence band discontinuity that causes a higher barrier height for holes flowing from source to drain. This indicated that the hot carrier is also affected by current drive.

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