半导体英文课件-Motion and Recombination of Electrons and Holes.ppt

Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* 2.2.3 Drift Current and Conductivity J p n E unit area + + Jp = qpv A/cm2 or C/cm2·sec If p = 1015cm-3 and v = 104 cm/s, then Jp= 1.6?10-19C ? 1015cm-3 ? 104cm/s = EXAMPLE: Hole current density Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* Jp,drift = qpv = qp?pE Jn,drift = –qnv = qn?nE Jdrift = Jn,drift + Jp,drift = ? E =(qn?n+qp?p)E conductivity (1/ohm-cm) of a semiconductor is ? = qn?n + qp?p 2.2.3 Drift Current and Conductivity 1/? = is resistivity (ohm-cm) Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* N-type P-type Relationship between Resistivity and Dopant Density ? = 1/? DOPANT DENSITY cm-3 RESISTIVITY (??cm) Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* EXAMPLE: Temperature Dependence of Resistance (a) What is the resistivity (?) of silicon doped with 1017cm-3 of arsenic? Solution: (a) Using the N-type curve in the previous figure, we find that ? = 0.084 ?-cm. (b) What is the resistance (R) of a piece of this silicon material 1?m long and 0.1 ?m2 in cross-sectional area? (b) R = ?L/A = 0.084 ?-cm ? 1 ?m / 0.1 ?m2 = 0.084 ?-cm ? 10-4 cm/ 10-10 cm2 = 8.4 ? 10-4 ? Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* EXAMPLE: Temperature Dependence of Resistance By what factor will R increase or decrease from T=300 K to T=400 K? Solution: The temperature dependent factor in ? (and therefore ?) is ?n. From the mobility vs. temperature curve for 1017cm-3, we find that ?n decreases from 770 at 300K to 400 at 400K. As a result, R increases by Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* 2.3 Diffusion Current Particles diffuse from a higher-concentration location to a lower-concentration location. Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 2-* 2.3 Diffusion Current D is called the di