MIT6_012S09_lec03

MIT6_012S09_lec03 - Lecture 3 Semiconductor Physics (II)...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Lecture 3 Semiconductor Physics (II) Carrier Transport Outline Thermal Motion Carrier Drift Carrier Diffusion Reading Assignment: Howe and Sodini; Chapter 2, Sect. 2.4-2.6 6.012 Spring 2009 Lecture 3 1 1. Thermal Motion Undergo collisions with vibrating Si atoms ( Brownian motion ) Electrostatically interact with each other and with ionized (charged) dopants In thermal equilibrium, carriers are not sitting still: Characteristic time constant of thermal motion: mean free time between collisions c collison time [ s ] In between collisions, carriers acquire high velocity: v th thermal velocity [ cms 1 ] . but get nowhere! 6.012 Spring 2009 Lecture 3 2 Characteristic length of thermal motion: mean free path [cm] = v th c Put numbers for Si at room temperature: c 10 13 s v th 10 7 cms 1 0.01 m For reference, state-of-the-art production MOSFET: L g 0.1 m Carriers undergo many collisions as they travel through devices 6.012 Spring 2009 Lecture 3 3 2. Carrier Drift Apply electric field to semiconductor: E electric field [V cm-1 ] net force on carrier F = qE Between collisions, carriers accelerate in the direction of the electrostatic field: v ( t ) = a t = qE m n , p t E 6.012 Spring 2009 Lecture 3 4 But there is (on the average) a collision every c and the velocity is randomized: The average net velocity in direction of the field: v = v d = qE 2 m n , p c = q c 2 m n , p E This is called drift velocity...
View Full Document

Page1 / 17

MIT6_012S09_lec03 - Lecture 3 Semiconductor Physics (II)...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online