# Why does LED shunt resistance decrease with increasing T?

• Kara386
In summary, the shunt resistance of a diode is caused by the finite bandgap and the thermal population of charge carriers.
Kara386
I'm not entirely clear what shunt resistance is, it's fairly hard to find things on google which refer to it in the context of LEDs. So we did an experiment in which we measured the IV characteristics of InAs at different temperatures, and observed the gradients of these graphs (apparently those give the shunt resistance?) to be decreasing with increasing temperature.

As far as I understand, this shunt resistance is something caused by manufacturing defects. So why would temperature have an effect? I have not got an extensive mathematical knowledge of the subject so qualitative answers would be really helpful, although if the maths is accessible I'd definitely be interested in seeing it! Thanks for any help! :)

Kara386 said:
'm not entirely clear what shunt resistance is, it's fairly hard to find things on google which refer to it in the context of LEDs. So we did an experiment in which we measured the IV characteristics of InAs at different temperatures, and observed the gradients of these graphs (apparently those give the shunt resistance?) to be decreasing with increasing temperature.

Kara386 said:
I'm not entirely clear what shunt resistance is, it's fairly hard to find things on google which refer to it in the context of LEDs. So we did an experiment in which we measured the IV characteristics of InAs at different temperatures, and observed the gradients of these graphs (apparently those give the shunt resistance?) to be decreasing with increasing temperature.

As far as I understand, this shunt resistance is something caused by manufacturing defects. So why would temperature have an effect? I have not got an extensive mathematical knowledge of the subject so qualitative answers would be really helpful, although if the maths is accessible I'd definitely be interested in seeing it! Thanks for any help! :)

Diodes is general are not perfect that is why with a reverse bias there is a small measurable current flowing. The shunt resistance is the ratio of the voltage change to the current change in the VI curve at
v ≅ 0

Temperature sensitivity in the characteristics of semiconductor device is to be expected. Temperature increases the energy of electrons in the semiconductor raising more into the conduction band from the valence band thus reducing resistance.

Kara386
gleem said:
Diodes is general are not perfect that is why with a reverse bias there is a small measurable current flowing. The shunt resistance is the ratio of the voltage change to the current change in the VI curve at
v ≅ 0

Temperature sensitivity in the characteristics of semiconductor device is to be expected. Temperature increases the energy of electrons in the semiconductor raising more into the conduction band from the valence band thus reducing resistance.

I would like to discourage the notion that shunt resistance of a diode is "something caused by manufacturing defects". When glee says "diodes are not perfect" he means real diodes do not behave as ideal diodes. However I want to make clear that for the most part that is not because of some manufacturing defect that can be made better. It is an intrinsic characteristic of a semiconductor. The band gap is finite. The temperature is finite, so there will always be a thermal population of charge carriers in the conduction band as given by the Fermi distribution. As glee points out this is also the reason for the variation with temperature. These thermal charge carriers mean a semiconductor will always act at least partially like a conductor. That's the reason for the name after all.

Kara386
Cutter Ketch said:
I would like to discourage the notion that shunt resistance of a diode is "something caused by manufacturing defects". When glee says "diodes are not perfect" he means real diodes do not behave as ideal diodes. However I want to make clear that for the most part that is not because of some manufacturing defect that can be made better. It is an intrinsic characteristic of a semiconductor. The band gap is finite. The temperature is finite, so there will always be a thermal population of charge carriers in the conduction band as given by the Fermi distribution. As glee points out this is also the reason for the variation with temperature. These thermal charge carriers mean a semiconductor will always act at least partially like a conductor. That's the reason for the name after all.
In an ordinary resistor though, increasing temperature increases resistance. What makes this type of resistance different? In an circuit with an ordinary resistor would adding more electrons result in lower resistance too?

Kara386 said:
In an ordinary resistor though, increasing temperature increases resistance. What makes this type of resistance different? In an circuit with an ordinary resistor would adding more electrons result in lower resistance too?

Yes! Exactly. That's one of those tell tale signs that something is different. In a resistor the higher temperature means there are more lattice vibrations, and so more phonon states for an unfortunate charge carrier to interact with and so higher resistance. This happens in a semiconductor too. However the very rapid increase in the number of charge carriers with temperature completely trumps the fact that each of them has a little tougher time getting around. So the resistance goes down.

Kara386
Cutter Ketch said:
Yes! Exactly. That's one of those tell tale signs that something is different. In a resistor the higher temperature means there are more lattice vibrations, and so more phonon states for an unfortunate charge carrier to interact with and so higher resistance. This happens in a semiconductor too. However the very rapid increase in the number of charge carriers with temperature completely trumps the fact that each of them has a little tougher time getting around. So the resistance goes down.

Kara386 said:
You are welcome.

## 1. Why does LED shunt resistance decrease with increasing T?

LED shunt resistance decreases with increasing temperature because the energy gap between the valence and conduction bands of the LED material decreases, resulting in a higher number of charge carriers and lower resistance.

## 2. How does temperature affect the shunt resistance of an LED?

Temperature has a direct impact on the shunt resistance of an LED. As the temperature increases, the shunt resistance decreases due to the increase in charge carriers and decrease in energy gap.

## 3. Is there an ideal temperature range for LED shunt resistance?

Yes, there is an ideal temperature range for LED shunt resistance. Generally, lower temperatures result in higher shunt resistance, but too low temperatures can also lead to decreased efficiency and performance of the LED.

## 4. Can external factors also affect the shunt resistance of an LED?

Yes, external factors such as humidity and exposure to certain chemicals can also affect the shunt resistance of an LED. These factors can alter the material properties of the LED, resulting in changes in shunt resistance.

## 5. How does the shunt resistance of an LED impact its overall performance?

The shunt resistance of an LED plays a crucial role in its overall performance. A lower shunt resistance can result in decreased efficiency and stability of the LED, while a higher shunt resistance can lead to better performance and longer lifespan of the LED.

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