Hello Yesterday in lab we were asked why all of our green LE

Hello,

Yesterday in lab, we were asked why all of our green LED had large forward voltage than expected. We expected for the forward voltage to be at around 2.1V as according to hf=Egap=eV.

Yet, we experienced forward voltages of 2.6-2.7 for our LEDs in the lab. Professor said that there is a reason, but I cannot seem to figure it out. Can I get help?

Solution

eV = hf

V = hf/e

h is planks constant

e is charge of an electron

f is frequency

i.e. Voltage drop is directly proportional to the frequency

All LED have different frequency with respect to their colours

Typically, the forward voltage of an LED is about 1.6–3.3 volts; it varies by the color of the LED. A red LED typically drops 1.6, but voltage drop normally rises as the light frequency increases, so a blue LED may drop around 3.3 volts.

# VIBGYOR -

Red has least frequency and violet has most and green is in between both of them

This is the reason for more voltage drop in green LED