Drift Transport

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Carrier Transport in Semiconductors

When an electric field is applied to a semiconductor, carrier transport occurs. Electrons move in the opposite direction of the electric field, while holes move in the same direction as the electric field.

Drift Transport in the Presence of an Electric Field

In the absence of an electric field, carriers move randomly at a constant velocity. However, when an electric field is present, carriers experience an acceleration in the direction of the field (for holes) or opposite to the field (for electrons). This acceleration causes a net motion of carriers in a specific direction, known as drift transport.

The movement of carriers due to an electric field is characterized by mobility, which varies between different semiconductor materials. For example, silicon, a commonly used semiconductor in photovoltaic applications, has specific mobility values.

Drift Equation, Conductivity, and Mobility

The one-dimensional drift equation is represented by a formula that considers current density, electric field, electron charge, electron and hole concentrations, electron and hole mobilities. This equation describes the behavior of carriers under the influence of an electric field.

When an electric field is applied, each electron experiences a net force leading to acceleration opposite to the field direction. The acceleration due to the electric field is balanced by deceleration from collision processes, resulting in a steady-state current flow.

The drift speed of carriers, conductivity of the semiconductor, and mobility of carriers are important factors in understanding carrier transport in semiconductors. The current density is determined by the number of carriers crossing a unit area per unit time, which is influenced by the conductivity and mobility of the carriers.

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