The correct option is **A. trivalent atoms**. ### Detailed Explanation: 1. **Understanding Silicon and Doping**: - Silicon (Si) is a semiconductor material that has four valence electrons. This means that in its crystalline structure, each silicon atom forms four covalent bonds with its neighboring silicon atoms. - Doping is the process of intentionally introducing impurities into a semiconductor to change its electrical properties. The type of dopant used determines whether the semiconductor becomes n-type or p-type. 2. **Types of Dopants**: - **Trivalent Atoms**: These are elements that have three valence electrons. Common trivalent dopants include boron (B), aluminum (Al), and gallium (Ga). When a trivalent atom is added to silicon, it creates a "hole" in the crystal structure because it can only form three bonds instead of four. This hole can accept an electron, effectively allowing for the conduction of electricity through the movement of these holes. This process creates a p-type semiconductor. - **Tetravalent Atoms**: These are elements with four valence electrons, like silicon itself. Adding tetravalent atoms to silicon does not change its properties significantly, as they can bond perfectly with the silicon atoms without creating holes or excess electrons. - **Pentavalent Atoms**: These are elements with five valence electrons, such as phosphorus (P) and arsenic (As). When pentavalent atoms are added to silicon, they provide an extra electron, which leads to the formation of n-type semiconductors, not p-type. - **Hexavalent Atoms**: These are elements with six valence electrons, like sulfur (S) and selenium (Se). Adding hexavalent atoms to silicon is not common in semiconductor doping and would not create a p-type semiconductor. 3. **Why Option A is Correct**: - When trivalent atoms are introduced into silicon, they create holes in the crystal lattice. These holes can move through the lattice and carry positive charge, which is the defining characteristic of p-type semiconductors. The presence of these holes allows for the conduction of electricity, albeit through a different mechanism than n-type semiconductors, which rely on the movement of excess electrons. 4. **Why Other Options are Incorrect**: - **Option B (Tetravalent Atoms)**: This option is incorrect because tetravalent atoms do not create holes or excess electrons; they simply bond with silicon without altering its electrical properties. - **Option C (Pentavalent Atoms)**: This option is incorrect because pentavalent atoms add extra electrons to the silicon lattice, resulting in n-type semiconductors, not p-type. - **Option D (Hexavalent Atoms)**: This option is incorrect as hexavalent atoms do not typically participate in the doping process for silicon semiconductors and would not create the necessary holes for p-type conduction. ### Summary: - Pure silicon can be converted to a p-type semiconductor by adding trivalent atoms (like boron). - Trivalent atoms create holes in the silicon lattice, allowing for positive charge conduction. - Tetravalent atoms do not change the properties of silicon, while pentavalent atoms create n-type semiconductors. - Hexavalent atoms are not used in the doping process for silicon semiconductors. ### Revision Summary: - **Doping**: The process of adding impurities to semiconductors to change their electrical properties. - **P-type Semiconductor**: Formed by adding trivalent atoms, creating holes for positive charge conduction. - **N-type Semiconductor**: Formed by adding pentavalent atoms, providing extra electrons for conduction. - **Trivalent Dopants**: Include boron, aluminum, and gallium, essential for creating p-type silicon.