can someone help me with this Semiconductor band gaps. A pure, defect-free, semi

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can someone help me with this

Semiconductor band gaps. A pure, defect-free, semiconductor material will absorb the electromagnetic radiation incident on it only if the energy of the individual photons in the incident beam is larger than a threshold value known as the "band gap" of the semiconductor. Otherwise, the material will be transparent to the photons. The room-temperature band gaps for germanium, silicon, and gallium, three widely used semiconductor, determine the threshold wavelength for it to be transparent. Also, say whether they are transparent for wavelengths longer or shorter than those threshold values. Zinc selenide (ZnSe) is a semiconductor with a room-temperature band gap of 2.67 eV. Using that bit of information, explain why ZnSe crystals have a yellow color. The telecommunication industry makes widespread use of infrared light with wavelength 1550 nm for optical fiber transmission. Which one or more of the four materials mentioned above would be suitable to make a detector for 1550nm light? )Hint: a detector needs to be able to absorb the light.)

Explanation / Answer

as energy=h*c/wavelength

so wavelength should be shorter than the threshold value to overcome the bandgap.

for germanium:

wavelength=1882.4 nm

for silicon:

wavelength=1109.3 nm

for gallium arsenide:

wavelength=874.9 nm

b)ZnSe has band gap of 2.67 eV

so wavelength absorbed=465.3 nm

so all other wavelength is absorbed and as yellow has 570nm wavelegnth,it gets reflected.

c)wavelength=1550 nm

energy=0.8015 eV

as detector needs to absorb light,the band gap should be smaller than this.

so the material used is GERMANIUM

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