NEET Physics Semiconductor Electronics Notes

Semiconductor Electronics

If a p.d. is applied across an intrinsic semiconductor the current
I = I_e + I_h

Where Ie is the current due to electrons and I is the current due to holes

For semiconductors (Eg < 3eV)

\(\left(\mathrm{E}_{\mathrm{g}}\right)_{\mathrm{Ge}}=0.71 \mathrm{eV},\left(\mathrm{E}_{\mathrm{g}}\right)_{\mathrm{Si}}=1.1 \mathrm{eV}\)
For insulators, Eg > 3eV
In an intrinsic semiconductor \(n_e=n_h\)

In n–type semiconductor \(n_e \gg>n_h\)
In p–type semiconductor \(n_h \gg n_e\)
In an extrinsic semiconductor,

\(\mathrm{n}_{\mathrm{e}} \mathrm{n}_{\mathrm{h}}=\mathrm{n}_{\mathrm{i}}^2\)

Where n_i= intrinsic carrier concentration.

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In a pn junction,
With of depletion region \(\propto \frac{1}{\text { Doping }}\)

The current gain in the CB mode of a transistor is given by

\(\alpha_{d c}=\frac{I_c}{I_E}\)

The current amplification factor is

\(\alpha_{\mathrm{ac}}=\left(\frac{\Delta \mathrm{I}_{\mathrm{c}}}{\Delta \mathrm{I}_{\mathrm{B}}}\right)_{\mathrm{V}_{\mathrm{CB}}=\text { constant }}\)

The current gain in CE mode is given by,

\(\beta_{\mathrm{dk}}=\frac{\mathrm{I}_{\mathrm{c}}}{\mathrm{I}_{\mathrm{B}}}\)

The current amplification factor is given by

\(\beta_{x c}=\left(\frac{\Delta I_c}{\Delta I_B}\right)_{V_{C S-c o c e t a n t}}\)

w.k.t., I_E = I_c + I_B

\(\frac{I_E}{I_C}=1+\frac{I_B}{I_C}\) \(\Rightarrow \frac{1}{\alpha_{\mathrm{de}}}=1+\frac{1}{\beta_{\mathrm{de}}}=\frac{\beta_{\mathrm{de}}+1}{\beta_{\mathrm{de}}}\) \(\Rightarrow \frac{1}{\alpha_{\mathrm{dc}}}-1=\frac{1}{\beta_{\mathrm{dc}}}=\frac{1-\alpha_{\mathrm{dc}}}{\alpha_{\mathrm{dc}}}\) \(\begin{array}{r}
\alpha_{\mathrm{dc}}=\frac{\beta_{\mathrm{dc}}}{\beta_{\mathrm{dc}}+1} \\
\Rightarrow \beta_{\mathrm{dc}}=\frac{\alpha_{\mathrm{de}}}{1-\alpha_{\mathrm{de}}}
\end{array}\)

Voltage gain in an amplifier,

\(A_v=\frac{V_0}{V_i}=-\frac{R_L \Delta I_C}{r \Delta I_B}\)

Where RL is loud resistance,

r is the input resistance

\(A_V=-\frac{\beta_{x c} R_L}{r}\)

Power gain = \(\mathrm{A}_V \times \mathrm{A}_1\)

\(=A_V \times \beta_x=-\frac{\beta_{x c}^2 R_L}{r}\)

\(A_V=\frac{I_C R_o}{I_B R_i}=\beta \frac{R_0}{R_i}\) \(A_P=\beta^2 \frac{R_0}{R_i}\)

where Ro and Ri are the output and input resistances respectively.

OR Gate

NEET Physics Semiconductor Electronics OR Gate

AND Gate

NEET Physics Semiconductor Electronics AND Gate

Note:

OR gate is equivalent to the parallel switching circuit

AND gate is equivalent to the series switching circuit

NOT Gate

NEET Physics Semiconductor Electronics NOT Gate

NAND Gate

NEET Physics Semiconductor Electronics NAND Gate

NOR Gate

NEET Physics Semiconductor Electronics NOR Gate

NOT Gate Using ‘NAND’ Gate

NEET Physics Semiconductor Electronics NOT Gate Using ‘NAND’ Gate

AND Gate Using NAND Gate

NEET Physics Semiconductor Electronics AND Gate Using NAND Gate

OR Gate From NAND Gate

NEET Physics Semiconductor Electronics OR Gate From NAND Gate

Basic Laws of Boolean Algebra

Boolean Postulates:

0 + A = A

1 . A = A

1 + A = 1

0 . A = 0

\(\mathrm{A}+\overline{\mathrm{A}}=1\)

Identify law:

A + A = A, A. A = a

Negation law:

\(\overline{\mathrm{A}}=\mathrm{A}\)

Commutative law:

A + B = B + A

A . B = B. A

Association law:

(A + B) + C = A + (B + C)

(A. B) . C = A . (B . C)

Distribute law:

A . (B + C) = A . B + A . C

NEET Physics Semiconductor Electronics Notes