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Analysis and Test of Diffusion Layer Quality

Author: Source: Datetime: 2016-09-28 17:14:24
Diffusion of the quality of solar power batteries has an important role in good or bad, which spread out the diffusion layer has certain requirements. The quality of the diffusion layer can basically be reflected from the following points: the depth of diffusion (junction depth), the diffusion layer of the sheet resistance.

Definition of diffusion junction depth and junction depth

Junction depth refers to the silicon doped with different types of conductive impurities, the distance from the surface of the silicon X, the impurity concentration of doped silicon impurity concentration and the same body, that is, in this position to form a PN junction, X Known as junction depth.

Factors that affect junction depth

Substrate impurity concentration: In the same distribution, the greater the substrate impurity concentration, the smaller the junction depth. Therefore, the depth of diffusion of the highly doped substrate is relatively shallow. Surface concentration: the normal distribution, the lower the surface concentration, the diffusion into the body the smaller the total amount of impurities, solar power batteries the more shallow junction depth. However, the surface concentration and the temperature is not so much, so by changing the surface concentration to control the effect of depth is not obvious.
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Diffusion time: junction depth X; proportional to the square root of the diffusion time. The effect of diffusion time on junction depth is less pronounced than other factors. For example, if the error of X is required to be less than 5%, as long as the error in diffusion time t is less than 6 min (calculated as the total time 1 h).

Diffusion temperature: temperature on the junction of great influence, such as silicon at 1180 ℃ for boron, as long as the temperature deviation ± 1 ℃, junction depth can be a difference of 5%, so to accurately control the spread of temperature to do the work.

Block resistance

The sheet resistance of the diffusion layer is also called the sheet resistance. In the solar power batteries diffusion process, the diffusion layer sheet resistance is to reflect the quality of the diffusion layer is consistent with the design requirements of one of the important process indicators. The impurity profile of the diffusion layer is determined for a pair of determined values of junction depth and sheet resistance. The sheet resistance refers to the resistance of a semiconductor thin layer with a square surface in the current direction (the current direction is parallel to the side of the square), denoted by the symbol R, as long as the shape of the diffusion layer is square, The size of the block resistance are the same, so the unit is in fact ohmmeter resistance.Solar power batteries used very broad such as solar powered portable generator,bank power
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Is the average conductivity of the diffusion layer. The size of the sheet resistance is proportional to the average resistivity of the thin layer, inversely proportional to the thickness of the thin layer, solar power batteries ndependent of the side length of the square. The value of the sheet resistance is determined by the total amount of carriers in the diffusion layer, which reflects the conductivity of the diffusion layer. The specific block resistance is measured by a four-probe method.

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