Silicon wafers
What is the main use of low-resistivity n⁺ silicon wafers heavily doped with arsenic or antimony?
- AAs the light-absorbing layer of an image sensor itself
- BAs the anti-reflection coating of a solar cell
- CAs substrates for growing lightly doped epitaxial layers, and as the drain-side substrate of vertical power devices
Show answer and explanation
Answer: C. As substrates for growing lightly doped epitaxial layers, and as the drain-side substrate of vertical power devices
Heavily doped, low-resistivity n⁺ wafers serve as substrates for epitaxial wafers with a lightly doped epitaxial layer on top. In vertical power MOSFETs and similar devices, current flows vertically through the substrate, so a low-resistance substrate reduces on-resistance.
- A. Lightly doped layers are used for light absorption.
- B. Anti-reflection coatings are films such as nitride, not the substrate's role.
- C. Correct. They serve as epi substrates and substrates for vertical power devices.