What Determines the Forward Voltage of an LED at low Currents?

[nocilis]

A number of years ago I required a low voltage, extremely low current, voltage regulator.

Normal Zener diodes do not function well at low currents.

I became aware that the forward voltage of red LED's was approximately 1 Volt at even extremely low currents (less than 1 microamp).

My question is (and I have been unable to find an answer), what physical properties determine the forward voltage of LED's at low currents?

Manufacturer's data sheets all indicate that it is approximately 1 Volt at very low (zero?) current.

 

[skeptic2]

I understand it comes from the energy in electron volts of the light that the LED emits.

 

[oswaler]

The forward voltage of an LED at low currents is determined by several factors, including the materials used to make the LED, the doping levels of those materials, and the design of the LED itself.

One of the main factors is the bandgap energy of the material used for the LED's semiconductor layer. This energy is directly related to the wavelength of light that the LED emits. For red LEDs, the bandgap energy is typically around 1.8-2.2 electron volts (eV). This means that in order for the LED to emit light, the electrons need to overcome this energy barrier and flow from the n-type semiconductor to the p-type semiconductor.

At low currents, the number of electrons flowing through the LED is very small. This means that the voltage required to overcome the bandgap energy and allow electrons to flow is also very small. In red LEDs, this voltage is typically around 1 volt, as you have observed.

Another factor that affects the forward voltage of an LED at low currents is the doping levels of the semiconductor layers. Doping refers to the intentional introduction of impurities into the semiconductor material to alter its electrical properties. In LEDs, different doping levels can affect the bandgap energy and therefore the forward voltage at low currents.

Finally, the design of the LED itself can also impact the forward voltage at low currents. This includes factors such as the thickness of the semiconductor layers, the size and shape of the LED, and the type of contacts used. All of these can affect the flow of electrons through the LED and therefore the forward voltage at low currents.

In summary, the forward voltage of an LED at low currents is determined by the bandgap energy of the material, the doping levels of the semiconductor layers, and the design of the LED. These factors work together to create a voltage barrier that must be overcome in order for the LED to emit light.