1. LED I-V Characteristic
Contents
1. P-N junction mechanism
2. Ideal I–V characteristic
3. Deviations from the ideal I–V
characteristic

2. P-N Junction Mechanism
Zero Bias

3. Ideal I–V characteristic
Basical assumption
a. All dopants are fully ionized
b.No compensation of the dopants
c. Bias voltage drops only across depletion region
d. Ignore excess current caused by carrier generation and recombination
D n,p- diffusion constants
A –Cross-section area
Ʈ n,p- minority-carrier lifetimes
N A,D-donor and acceptor concentration
n i -intrinsic carrier concentration
Shockley equation
Diffusion voltage
In case that V >> kT / e,

4. According to Boltzmann statistics
Thus,
Highly doped semiconductors
(E C – E F ) << E g
(E F – E V ) << E g
Thus,

6. is the forbidden band gap at 0 K
Current VS Temperature
is the forbidden band gap at 0 K
is a positive constant

7. Recombination current dominates only at low voltages
Deviations from the ideal I–V characteristic
a. Generation current
b. Recombination Current
XD-width of depletion region
Ʈ-minority-carrer lifetimes （非平衡电子空穴对每复合一次所需的平均时间）
势垒区产生电流在在反相偏压下才出现
势垒区复合电流在正向偏压下才会出现
Lp-空穴扩散长度
IFD-扩散电流，即正偏压下的理想电流
nideal -Ideality Factor of the diode, V
Recombination current dominates only at low voltages

8. c. Parasitic Resistances
Series resistance: excessive contact resistance, resistance of the neutral regions.
Parallel resistance: caused by any channel that bypasses the p-n junction, such
as damaged regions of the p-n junction, surface imperfections
I–V characteristic of a forward-biased p-n junction diode

9. Thanks