Semiconductores 01, Estructura Atomica, Intrínseco, Extrínseco, Impurezas pentavalentes, trivalentes

Semiconductor Basics

In this section, the speaker introduces the topic of semiconductors and their significance in modern electronics. The discussion begins with an exploration of atomic structure to lay the foundation for understanding semiconductors.

Atomic Structure and Valence Electrons

• Atoms consist of a nucleus containing protons (positively charged) and neutrons, with electrons orbiting around it.

• The atomic number indicates the number of protons in an atom, determining its electron configuration.

• Electrons are arranged in valence shells or energy levels around the nucleus.

• Electrons closer to the nucleus experience stronger attraction compared to those in outer shells.

• Electrons in the outermost shell can be easily excited or removed, becoming free electrons.

Semiconductor Materials: Copper, Germanium, Silicon

• Copper has 29 protons and electrons distributed across different valence shells.

• Copper's single valence electron makes it a good conductor due to easy excitation to become a free electron.

• Germanium has 32 electrons with four valence shells, while silicon has 14 electrons with three valence shells.

• Both germanium and silicon exhibit semiconductor properties due to their specific electron configurations.

Importance of Semiconductors

• Gold and copper are excellent conductors; however, silicon is preferred as a semiconductor due to its abundance on Earth.

Semiconductor Basics

In this section, the speaker delves into the fundamentals of semiconductors, focusing on silicon crystals and their behavior as conductors or insulators based on electron sharing.

Germanium and Silicon Crystal Structure

• Silicon atoms form a crystal structure when they come close together, sharing electrons in what is known as a covalent bond.

Lewis' Rule of Octet and Semiconductor Behavior

• Gilbert Newton Lewis introduced the rule of octet in 1917, stating that atoms tend to complete their valence shells with eight electrons for stability.

• This leads to the formation of a stable structure with no free electrons, behaving as a perfect insulator according to Lewis' rule.

Conductors, Insulators, and Semiconductors

• Conductors have low resistance due to easily generated free electrons upon excitation.

• Insulators resist electron flow even with high excitation levels.

• Semiconductors exhibit properties between conductors and insulators based on electron behavior under thermal energy.

• When excited, silicon crystals may produce some free electrons due to electron transitions within the valence band.

• The absence of free electrons in pure silicon categorizes it as an intrinsic semiconductor acting as an insulator until thermally excited.

Doping and Semiconductor Types

This segment explores doping processes in semiconductors through introducing impurities to alter conductivity levels.

Introduction to Holes and Electrons

• Exciting a silicon crystal can create holes (positive charges) when electrons leave their valence positions.

• These holes attract nearby electrons upon exposure to electric current, leading to recombination without any free charges left in the crystal.

• A pure silicon crystal exhibiting this behavior is termed an intrinsic semiconductor due to its ability to generate both holes and free electrons under thermal energy conditions.

Intrinsic vs. Extrinsic Semiconductors

• An intrinsic semiconductor contains both holes and free electrons naturally but behaves primarily as an insulator unless thermally excited.

• Doping introduces impurities like pentavalent atoms (e.g., arsenic) into pure silicon crystals, increasing conductivity by providing additional free electrons per atom added.

• Manufacturers control conductivity by adjusting the number of pentavalent impurities added; more impurities lead to higher conductivity levels.

• Weakly doped semiconductors have high resistance while heavily doped ones exhibit low resistance due to increased donor impurity contributions.

Types of Doping: N-Type and P-Type Semiconductors

This part discusses n-type and p-type semiconductors resulting from doping processes using different types of impurities.

Donor Impurities in N-Type Semiconductors

• Adding pentavalent impurities creates n-type semiconductors where each atom contributes an extra negative charge for enhanced conductivity.

• The excess free electrons facilitate electrical conduction within the crystal structure.

• A crystal doped with such impurities is labeled as an n-type semiconductor due to its negative charge carriers.

Acceptor Impurities in P-Type Semiconductors

• Introducing trivalent acceptor impurities like boron into intrinsic semiconducting materials generates p-type semiconductors by creating holes that can accept additional free charges.

 - Each trivalent atom contributes a positive hole that attracts nearby electrons for conduction purposes. 

   - Such crystals are termed p-type semiconductors owing to their positive charge carriers derived from acceptor dopants.