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Home » Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 1028 atoms/m3 with 1ppm concentration of As. On the surface 200 ppm Boron is added to create the ‘P’ region in this wafer. Considering ni = 1.5 × 1016 m–3,
Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 1028 atoms/m3 with 1ppm concentration of As. On the surface 200 ppm Boron is added to create the ‘P’ region in this wafer. Considering ni = 1.5 × 1016 m–3,
CBSE | Class 12 | NCERT Exemplar | Physics | Semiconductor Electronics: Materials, Devices and Simple Circuits
Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 1028 atoms/m3 with 1ppm concentration of As. On the surface 200 ppm Boron is added to create the ‘P’ region in this wafer. Considering ni = 1.5 × 1016 m–3,

(i) Calculate the densities of the charge carriers in the n & p regions.

(ii) Comment which charge carriers would contribute largely for the reverse saturation current when the diode is reverse biased.

Answer:

When As (pentavalent) is added to Si, n-type water is produced, with the following number of predominant carriers:

{{n}_{h}}={{N}_{D}}\times n(Si)

{{n}_{h}}=\frac{200}{{{10}^{6}}}\times 5\times {{10}^{28}}=1000\times {{10}^{22}}

{{n}_{h}}=1\times {{10}^{25}}holes/{{m}^{3}}

Minority carrier in p-type wafer are:

{{n}_{e}}{{n}_{h}}=n_{i}^{2}

{{n}_{e}}=\frac{n_{i}^{2}}{{{n}_{h}}}=\frac{1.5\times {{10}^{16}}\times 1.5\times {{10}^{16}}}{{{10}^{25}}}

{{n}_{e}}=2.25\times {{10}^{7}}electrons/{{m}^{3}}

ii) When the diode is reverse biassed, the n-region minority carrier holes contribute significantly to the reverse saturation current. When reversed bias is given to a p-n junction, the minority charge carrier, which is holes from the n side and electrons from the p side, flows toward the depletion layer, thickening the depletion layer.

i

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