Which of the following statements are correct:
A. In semiconductor diodes carriers are generated by photo-excitation.
B. When the photo diode is illuminated with light with energy \( (E) \gt \) Energy gap \( (E_g) \) of the semiconductor, then electron-hole pairs are generated.
C. Photovoltaic devices convert electricity into optical radiation.
D. Photodiode can be used as a photodetector to detect optical signal.
E. Zener diode specification should be taken as per the required output voltage.
Choose the correct answer from the following options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, B, D and E only
Optoelectronic junction devices are semiconductor diodes in which carriers are generated by photons, that is, by photo-excitation.
A. In semiconductor diodes carriers are generated by photo-excitation. — Correct. In optoelectronic diodes the carriers are produced when photons are absorbed near the junction.
B. When the photo diode is illuminated with light with energy \( (E) \gt \) Energy gap \( (E_g) \) of the semiconductor, then electron-hole pairs are generated. — Correct. A photon with \( h\nu \gt E_g \) can lift an electron from the valence band to the conduction band, leaving a hole behind.
C. Photovoltaic devices convert electricity into optical radiation. — Incorrect. A photovoltaic device (solar cell) converts optical radiation into electricity; the reverse conversion is done by an LED.
D. Photodiode can be used as a photodetector to detect optical signal. — Correct. Under reverse bias the photocurrent of a photodiode changes with the intensity of the light falling on it, so it detects optical signals.
E. Zener diode specification should be taken as per the required output voltage. — Correct. In a voltage regulator the output voltage equals the Zener breakdown voltage \( V_Z \), so a Zener diode with \( V_Z \) equal to the required output voltage is chosen.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Optoelectronic Junction Devices – “… In this section, we learn about semiconductor diodes in which carriers are generated by photons (photo-excitation). All these devices are called optoelectronic devices. We shall study the functioning of the following optoelectronic devices: (i) Photodiodes used for detecting optical signal (photodetectors). … (iii) Photovoltaic devices which convert optical radiation into electricity (solar cells).”
Photodiode – “… When the photodiode is illuminated with light (photons) with energy (hν) greater than the energy gap (Eg) of the semiconductor, then electron-hole pairs are generated due to the absorption of photons. … Thus photodiode can be used as a photodetector to detect optical signals.”
Zener Diode – “… We have to select the Zener diode according to the required output voltage and accordingly the series resistance Rs.”