Turn-on voltage of pn junction diodes

[acinom]

Hey, I am working on a report and got stuck at two discussion questions. Help & discussion would be greatly appreciated!

1. What factors determine the turn-on voltage of a pn junction diode? Explain its dependence on the factors you mentioned

My guess would be that the light intensity on the diode would affect it due to excitation of electrons which will affect the electron-hole recombination and hence the depletion region width? I am also betting on temperature and also doping concentrations. Temperature will cause a shift in the I-V characteristic, thus changing the turn on voltage but am not sure why? As for doping concentrations... it's really a wild guess.

2. Explain the factors that influence the spectral linewidth of the emission spectrum.

Really stumped by this! I'm thinking that different semiconductor materials will have different spectral linewidths but not really sure about the theoretical basis behind it. Apparently it can be adjusted?

Thanks a lot in advance!

 

[nickjer]

This is definitely not introductory physics. Also, you might want to get a book on semiconductor processes or diodes because that question requires a lot of detail. You should look up the injection process under forward bias and see what affects it. Doping concentrations affect the Fermi level which is important in calculating the injection voltage as well as the band gap. But you will need a lot more reading and details to get a better understanding.

 

[nlightner]

I can provide some insights into the turn-on voltage of pn junction diodes and the factors that influence the spectral linewidth of the emission spectrum.

1. Factors determining the turn-on voltage of pn junction diodes:

a. Material properties: The properties of the semiconductor material used in the pn junction diode can greatly affect its turn-on voltage. For example, a higher bandgap material will have a higher turn-on voltage compared to a lower bandgap material.

b. Doping concentrations: As you mentioned, doping concentrations can also influence the turn-on voltage. This is because the doping level affects the width of the depletion region, which in turn affects the barrier for charge carriers to flow across the junction.

c. Temperature: Temperature has a significant impact on the turn-on voltage of a pn junction diode. As the temperature increases, the thermal energy of the charge carriers increases, making it easier for them to overcome the barrier and flow across the junction. This results in a decrease in the turn-on voltage.

2. Factors influencing the spectral linewidth of the emission spectrum:

a. Material properties: Again, the properties of the semiconductor material play a crucial role in determining the spectral linewidth of the emission spectrum. Different materials have different bandgaps and energy levels, which can result in varying emission wavelengths and linewidths.

b. Crystal structure: The crystal structure of the material can also affect the spectral linewidth. For example, a highly ordered and uniform crystal structure will result in a narrower linewidth compared to a disordered or non-uniform crystal structure.

c. Temperature: Similar to the turn-on voltage, temperature can also influence the spectral linewidth. As the temperature increases, the thermal energy of the charge carriers increases, resulting in a broader linewidth.

d. External factors: External factors such as strain, pressure, and electric fields can also influence the spectral linewidth of the emission spectrum. These factors can alter the energy levels and band structure of the material, resulting in a change in the emission wavelength and linewidth.

I hope this helps in your report. Keep in mind that these are just some of the factors that can influence the turn-on voltage and spectral linewidth, and there may be others depending on the specific characteristics of the pn junction diode and the material used. Further research and experimentation may be needed to fully understand and control these factors.