Semiconductors: N-type, P-type, and Doping

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Questions and Answers

What are the two main classifications of semiconductors, and what distinguishes them?

Intrinsic (pure) and Extrinsic (impure) semiconductors. Intrinsic are pure, while extrinsic are doped with impurities.

In an intrinsic semiconductor, how does temperature affect the movement of electrons to the conduction band?

At room temperature, some valence electrons may acquire enough energy to enter the conduction band and become free electrons.

Explain the relationship between electron movement and 'holes' in a semiconductor.

Missing electrons in the valence band leave vacant spaces called 'holes,' which contribute to 'hole' current. Total current is the sum of electron and hole currents.

Describe how holes behave when a semiconductor is connected to a battery.

Holes, being positively charged, move towards the negative terminal of the battery and combine with electrons. Signup and view all the answers

Why is the intrinsic semiconductor not useful in electronic devices and, therefore, need some modifications?

Due to poor conduction at room temperature it needs some modifications with doping. Signup and view all the answers

What is doping, and why is it important in semiconductor technology?

Doping is adding impurities to a semiconductor to increase its current conduction capability. Signup and view all the answers

Describe the key difference between N-type and P-type semiconductors concerning their majority carriers.

N-type semiconductors have electrons as majority carriers, while P-type semiconductors have holes as majority carriers. Signup and view all the answers

In an N-type semiconductor, what type of impurity is added and which elements can be used?

Pentavalent impurities are added, such as arsenic, antimony, or phosphorus. Signup and view all the answers

How does doping with pentavalent impurities result in free electrons in an N-type semiconductor?

Pentavalent impurities form covalent bonds with semiconductor atoms, but the fifth electron is loosely bound and becomes a free electron. Signup and view all the answers

What are donor impurities and how are they relevant to n-type semiconductors?

Donor impurities are impurities that donate free electrons to the semiconductor structure, enhancing its conductivity. They are relevant to n-type semiconductors. Signup and view all the answers

Describe the types of impurities added to create a P-Type semiconductor and give an example.

Trivalent impurities such as aluminum or boron are added. Signup and view all the answers

Explain why trivalent impurities create holes in a P-type semiconductor.

Each boron atom contributes a 'hole' for conduction because it has one less electron than needed for covalent bonding. Signup and view all the answers

What are acceptor impurities and how are they relevant to P-type semiconductors?

Acceptor impurities are impurities that create holes in the semiconductor structure. They are relevant to p-type semiconductors. Signup and view all the answers

State the mass action law and explain its relevance to doped semiconductors.

Under thermal equilibrium, the product of the number of electrons and holes is constant and independent of doping. Signup and view all the answers

Explain how doping with N-type impurities affects the concentration of electrons and holes.

Increases the number of electrons in the conduction band and decreases the number of holes in the valence band. Signup and view all the answers

What is drift current, and what causes it in a semiconductor material?

Drift current is the flow of electric current due to the motion of charge carriers under the influence of an external electric field. Signup and view all the answers

What determines the direction of movement of electrons and holes in drift current?

Electrons move towards the positive terminal, while holes move towards the negative terminal of the battery. Signup and view all the answers

Define drift current density and explain what factors influence its magnitude.

Drift current density is the current passing through a square centimeter perpendicular to the direction of flow. Influenced by charge carrier density and drift velocity. Signup and view all the answers

What is the equation of drift current density, and what do the variables represent for holes?

$J_p = q p \mu_p E$, where $q$ is the charge of an electron, $p$ is the number of holes per cubic centimeter, $\mu_p$ is the mobility of holes, and $E$ is the applied electric field intensity. Signup and view all the answers

What is the equation of drift current density, and what do the variables represent for electrons?

$J_n = q n \mu_n E$, where $q$ is the charge of an electron, $n$ is the number of electrons per cubic centimeter, $\mu_n$ is the mobility of electrons, and $E$ is the applied electric field intensity. Signup and view all the answers

What condition in a semiconductor allows electric current flow even in the absence of an applied voltage?

A concentration gradient in the material permits electric current flow. Signup and view all the answers

Explain diffusion current and what causes it.

Diffusion current is the current resulting from the movement of charge carriers from a region of higher concentration to lower concentration. Signup and view all the answers

Describe the relationship between charge carrier concentration and the direction of diffusion current.

Charge carriers move from regions of higher concentration to regions of lower concentration. Signup and view all the answers

Relate the Einstein relationship in semiconductors.

The equation which relates the mobility M and diffusion coefficient D. Signup and view all the answers

What is diffusion length, and what parameters determine its value?

Average distance that an excess charge carrier can diffuse during its lifetime. Determined by the diffusion coefficient and lifetime. Signup and view all the answers

Describe how a PN junction is formed and the type of doping on each side.

A PN junction is formed by joining a P-type semiconductor (doped with acceptor impurities) and an N-type semiconductor (doped with donor impurities). Signup and view all the answers

What are the majority carriers on the P and N sides of a PN junction?

P side: holes. N side: electrons. Signup and view all the answers

When a PN junction is first formed, what process occurs and drives a significant change?

Diffusion: Free electrons from the N-side diffuse to the P-side, and holes from the P-side diffuse to the N-side. Signup and view all the answers

Explain why a space charge region or depletion region forms at the junction.

The space charge region is created by exposed ionized donors and uncovered acceptor ions. Signup and view all the answers

Define potential barrier and discuss how it relates to a PN-junction.

Barrier that prevents further movement of charge carriers. Known as diffusion or contact potential. Signup and view all the answers

What are the typical values of contact potential ($V_o$) for silicon and germanium?

0.7 V for silicon and 0.3 V for germanium. Signup and view all the answers

How does the charge of the space charge layers relate to the majority carriers and the setting of the junction?

The layers are of opposite sign to the majority carriers, which causes the E field to setup. Signup and view all the answers

Describe what is meant by the depletion width calculation.

Calculation of the edge of the P and N sides where depletion occurs. Signup and view all the answers

Define forward bias in a PN junction diode.

Applies a potential to the P-type by connecting + terminal to the P-type and - terminal to N-type. Signup and view all the answers

Describe some of the characteristics under the 'forward bias' state of the diode.

The forward current $I_F$ is almost zero if $V_F < V_o$. For $V_F > V_o$ complete disappearence of potential barrier. Hence, a steady external ciruit. Signup and view all the answers

Define reverse bias in a PN junction diode.

Connection with the - terminal of a battery to the P-type and + terminal to the N-type. Signup and view all the answers

When does a reverse saturation current $I_o$ occur and what are its characteristics?

A small constant current flows under reverse bias conditions due to minority carriers. It is independent of bias voltage. Signup and view all the answers

Describe the avalanche effect, and explain its relevance the diode functionality.

Avalanche multiplication occurs when carriers accelerated by a high electric field gain enough energy to ionize atoms, creating additional carriers. Signup and view all the answers

Relate in an equation The avalanche multiplication effect.

$M = \frac{1}{1-(\frac{V}{V_{BD}})^n}$ , where $M$ is carrier mulitiplication factor. Signup and view all the answers

What is Transition Capacitance ($C_T$) within the diode and what is its relationship with reverse voltage?

The space-charge layer width at the junction increases as reverse voltage is applied. $C_T$ is inversely related to voltage. Signup and view all the answers

Flashcards

Intrinsic Semiconductor

Pure semiconductor without impurities.

Extrinsic Semiconductor

Semiconductor with added impurities to alter conductivity.