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Lecture Electrical Engineering: Lecture 5 - Dr. Nasim Zafar

In this chapter, you will learn about: carrier transport in semiconductors, diffusion of carriers, diffusion processes, diffusion and recombination, continuity equations, einstein relation. | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Carrier Transport in Semiconductors Lecture No: 5 Diffusion of Carriers Diffusion Processes Diffusion and Recombination Continuity Equations Einstein Relation Nasim Zafar 2 Carrier Diffusion: Introduction: When excess carriers are created non-uniformly in a semiconductor, a “concentration gradient” results due to this non-uniformity of the carrier densities in the sample. This concentration gradient, for electrons and holes, will cause a net motion of the charge carriers from the regions of high density to the regions of low carrier density. This type of carrier motion is called Diffusion and represents an important charge transport process in semiconductors. Thus, the charge carriers in a semiconductor diffuse, due to the concentration gradient by random thermal motion and under going scattering from: The lattice vibrations and Ionized Impurity atoms. Carrier Diffusion: Introduction: When excess carriers are created non-uniformly in a semiconductor, a concentration gradient results due to this non-uniformity of the carrier densities in the sample. This concentration gradient, for electrons and holes, will cause a net motion of the charge carriers from the regions of high density to the regions of low carrier density. This type of carrier motion is called Diffusion and represents an important charge transport process in semiconductors. Carrier Diffusion: Introduction: Thus, the charge carriers in a semiconductor diffuse, due to the concentration gradient by random thermal motion and under going scattering from: The lattice vibrations and Ionized Impurity atoms. Carrier Diffusion: How can we produce a concentration gradient in a semiconductor? By making a semiconductor or metal contact. By illuminating a portion of the semiconductor with light, (next slide). As the carriers diffuse, a diffusion current flows. . | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Carrier Transport in Semiconductors Lecture No: 5 Diffusion of Carriers Diffusion Processes Diffusion and Recombination Continuity Equations Einstein Relation Nasim Zafar 2 Carrier Diffusion: Introduction: When excess carriers are created non-uniformly in a semiconductor, a “concentration gradient” results due to this non-uniformity of the carrier densities in the sample. This concentration gradient, for electrons and holes, will cause a net motion of the charge carriers from the regions of high density to the regions of low carrier density. This type of carrier motion is called Diffusion and represents an important charge transport process in semiconductors. Thus, the charge carriers in a semiconductor diffuse, due to the concentration gradient by random thermal motion and under going scattering from: The lattice vibrations and .