GATE EC 2019 Set 1 — Question 58
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Electronic Devices → Optoelectronic Devices → Optical Absorption
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Question
A Germanium sample of dimensions is illuminated with a 20 mW, 600 nm laser light source as shown in the figure. The illuminated sample surface has a 100 nm of loss-less Silicon dioxide layer that reflects one-fourth of the incident light. From the remaining light, one-third of the power is reflected from the Silicon dioxide-Germanium interface, one-third is absorbed in the Germanium layer, and one-third is transmitted through the other side of the sample. If the absorption coefficient of Germanium at 600 nm is and the bandgap is 0.66 eV, the thickness of the Germanium layer, rounded off to 3 decimal places, is ________ .
Correct answer
0.23 to 0.232
Solution
1.Incident power mW.
2.Power reflected from the top surface of is mW.
3.Remaining power entering is mW.
4.From this 15 mW, one-third is reflected at the -Ge interface, one-third is absorbed in Ge, and one-third is transmitted through Ge.
- Reflected at interface: mW.
- Absorbed in Ge: mW.
- Transmitted through Ge: mW.
6.According to the absorption law: , where is the absorption coefficient and is the thickness.
7..
8. cm.
9.Converting to micrometers: .
10.Rounded to 3 decimal places, .
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