SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

4.4. REAL DIODES:DEFECTS AND CARRIER GENERATION 169

( (

Region

1

Region

2

HIGH INJECTION

REGION

• Dominated by
  generation-
  recombination
  
  
  • Diode behaves
    like an ohmic
    resistor
  
  
  
  

FORWARD BIAS, V (volt)

Region

3

C

URRENT

I (A)

10 –3

10 –6

10 –9

10 –12

10 –15

0.2 0.4 0.6 0.8

VD

rS

I =

eV

kBT

exp –1

(

eV

2kBT

exp –1

(

Figure 4.14: A log plot of the diode current in forward bias. At low biases, the recombination
effects are quite pronounced, while at higher biases the slope becomes closer to unity. At still
higher biases the behavior becomes more ohmic.

us to solve forψ(x)and thusE(0).Thisgives

I◦GR =

(

1. 6 × 10 −^19 C

)(

10 −^3 cm^2

)(

1. 5 × 1010 cm−^3

)

2(10−^6 s)

·

(3.14) (. 026 V)

(3. 2 × 104 V/cm)

=3. 0 × 10 −^12 A

and

IGR = IGRo

[

exp

(

eV

2 kBT

)

− 1

]

We can see that the generation-recombination prefactor is much larger than the prefactor

due to the diffusion term. Thus the reverse current will be dominated by the

generation-recombination effects.

In forward bias, the diffusion current is initially much smaller than the

generation-recombination term. However, at higher forward bias the diffusion current will

start to dominate. For example, we see that at a forward bias of 0.2 V, the diffusion current

is 2. 2 × 10 −^11 A, while the generation-recombination current is 1. 65 × 10 −^10 A. At a