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# D/A conversion Semiconductors The density of carriers in a semiconductor PowerPoint PPT Presentation

D/A conversion Semiconductors The density of carriers in a semiconductor For silicon at room temperature: Drift current density: j = Qv , Q - charge density, v - velocity of charge in an electric field

D/A conversion Semiconductors The density of carriers in a semiconductor

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#### Presentation Transcript

D/A conversion

Semiconductors

The density of carriers in a semiconductor

For silicon at room temperature:

Drift current density: j = Qv, Q - charge density, v - velocity of charge in an electric field

jTdrift =jn + jp = q(n n + p p)E = E,  = q(n n + p p) (cm)-1 ,  = 1/ (cm)

Charge neutrality q(ND + p - NA - n) = 0; in thermal equilibrium: pn = ni2

For n-type: . If (ND - NA) >> 2ni, n (ND - NA)

Similarly for p-type.

Diffusion current , VT =kT/q, is approximately 25 mV,

• Total current

• or

pn-junction and Diodes

For reverse bias:

- diode equation.

whereIS=reverse saturation current (A) vD=voltage applied to diode (V)q=electronic charge (1.60 x 10-19 C)k=Boltzmann’s constant (1.38 x 10-23 J/K)T=absolute temperaturen=nonideality factor (dimensionless)VT=kT/q = thermal voltage (V) (25 mV at room temp.)

ISis typically between 10-18 and 10-9 A, and is strongly temperature dependent due to its dependence on ni2. The nonideality factor is typically close to 1

Rectifiers

Half-wave

Full wave