1.0. Semiconductor Diodes 1 of 27 1.2 Ideal Diode

ID

VD

ID

Open Circuit

Short CircuitVD

+ -

1.0. Semiconductor Diodes 2 of 27 1.3 Semiconductor Materials Conductor Insulator Semiconductor

R = (Resistivity, ρ ohm-cm) * (Length, L cm) / (Area, cm2) = RA/L R = (50,000 ohm-cm)(4 cm)/(2cm x 4cm) = 25,000 ohms Resistivity of a semiconductor decreases as temperature increases.

ure coefficient. Negative temperat

1.0. Semiconductor Diodes 3 of 27 Ge and Si single-crystal structure

Atomic structure: (a) germanium; (b) silicon.

1.0. Semiconductor Diodes 4 of 27 Energy Levels

1.0. Semiconductor Diodes 5 of 27

W = QV joules Q = 1.6 x 10-19 coulomb (1 electron worth of charge)(1V) = 1.6 x 10-19 Joule (1.6 x 10-19 coulomb)(1V) = 1.6 x 10-19 Joule 3 electrons and 2 volts 3 electrons have a charge = 4.8(10-19) comlomb 4.8(10-19 coulomb)(2 volts) = 9.6(10-19) Joule or 6eV

1.0. Semiconductor Diodes 6 of 27 1.5 Extrinsic Materials – doped

1.0. Semiconductor Diodes 7 of 27 (a) n-type material; (b) p-type material.

1.0. Semiconductor Diodes 8 of 27 1.6 Semiconductor Diode p-n junction with no external bias

Carriers combine, resulting in depletion region

1.0. Semiconductor Diodes 9 of 27 Reverse-biased p-n junction.

electrons holes

1.0. Semiconductor Diodes 10 of 27 Forward-biased p-n junction.

electronsholes

1.0. Semiconductor Diodes 11 of 27 Silicon semiconductor diode characteristics.

1.0. Semiconductor Diodes 12 of 27 ID = Is(ekV/T – 1) k constant, 11,600/η η= 1 for Ge and 2 for Si V diode forward voltage T temperature in Kelvin, 273o + temp in centigrade Example: Si, voltage = 0.7, k=5800, Is = -25nA

k 5800

K 273

TA 20

TK K TA

Is 25 10 9.

VD 0.7

ID Is ek

VDTK.

1. .02605004764852208305

1.0. Semiconductor Diodes 13 of 27

Peak Inverse Voltage - usually >50 volts

Tempers for every10o C increase in temperr every10o C increase in temperature

V_V1

-6.0V -5.0V -4.0V -3.0V -2.0V -1.0V -0.0V 1.0VI(D1)

-20mA

-10mA

0A

10mA

20mA

Zener region VT = 0.7 Si

ature effects

Current double ature VT decreases 2mv for every1o C VT decreases 2mv for every1o C

1.0. Semiconductor Diodes 14 of 27 1.8 Resistance Levels Diode I-V characteristic

DC Resistance

RD = VD / ID

V_V1

0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0VI(D1)

0A

10mA

20mA

30mA

Q-point Quiescent point Operating point

1V/15mA = 0.0667*1000 66.7

1.0. Semiconductor Diodes 15 of 27 AC or Dynamic Resistance

RD = ∆Vd / ∆Id

V_V1

0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0VI(D1)

0A

10mA

20mA

30mA

Q-point Quiescent point Operating point

for example at 25mA in Fig. 1.34 on page 22, RD = ∆Vd / ∆Id = (0.8V – 0.78V)/(30mA – 20mA) = 2 ohms

1.0. Semiconductor Diodes 16 of 27 Using calculus we get approx,

1/rD = dI/dV = d/dV (Is(ekV/T – 1) = Is (k/T) ekV/T

= (k/T) Is ekV/T

which is almost

1/rD = kID / T at room temp 25oC rd = 26mv / ID at 15mA, rd = 26mv / 15mA 1.733 ohms

rd’ = (26mv / ID) + rB , add diode body resistance

1.0. Semiconductor Diodes 17 of 27 Average AC resistance

1.0. Semiconductor Diodes 18 of 27 1.9 Diode Equivalent Circuits Piecewise-Linear Equivalent Circuit

1.0. Semiconductor Diodes 19 of 27

deal diode and its characteristics.

Simplified equivalent circuit for the silicon semiconductor diode.

I

1.0. Semiconductor Diodes 20 of 27 1.10 Diode Specification Sheets

1.0. Semiconductor Diodes 21 of 27 1.11 Transition and Diffusion Capacitance Reverse bias – capacitance of depletion region. CT Forward bias – excess charge injected into regions just outside the depletion region, CD.

1.12 Reverse Recovery Time Diffusion capacitance (charge stored). Reversing the bias sweeps the stored charge out.

1.0. Semiconductor Diodes 22 of 27 FIGURE 1-42 Transition and diffusion capacitance versus applied bias for a silicon diode.

At V = 0.25 the CD = 9pF At V = -15 the CT = 1pF

1.0. Semiconductor Diodes 23 of 27 1.13 Semiconductor Diode Notation 1.14 Diode Testing 1.15 Zener Diodes Conduction direction: (a) Zener diode; (b) semiconductor diode.

1.0. Semiconductor Diodes 24 of 27

1.0. Semiconductor Diodes 25 of 27 1.16 Light Emitting Diodes

(a) Process of electroluminescence in the LED; (b) graphic symbol.

1.0. Semiconductor Diodes 26 of 27

1.0. Semiconductor Diodes 27 of 27 1.17 Diode Arrays – Integrated Circuits 1.18 Summary 1.19 Computer Analysis