Distinguish Between Intrinsic and Extrinsic Semiconductor
Semiconductors are materials that have electrical conductivity between that of a conductor and an insulator. Their unique properties make them incredibly useful for controlling electrical currents and building various electronic devices.
Semiconductors can be classified into two main types: intrinsic and extrinsic. Though similar in some ways, intrinsic and extrinsic semiconductors have distinct properties that give each type certain advantages and applications. Understanding the key differences between intrinsic and extrinsic semiconductors is important for anyone working with semiconductor physics and electronics.
What is an Intrinsic Semiconductor?
An intrinsic semiconductor is a pure semiconductor that is not mixed with any impurities. Silicon and germanium are two common intrinsic semiconductor materials used in electronics.
In an intrinsic semiconductor, electrical conduction is due to the inherent thermal energy of the electron-hole pairs generated within the crystal lattice structure of the material. At absolute zero temperature, an intrinsic semiconductor acts as a perfect insulator since there is no thermal energy available to free electrons from their bonds.
As temperature increases, some electrons gain enough thermal energy to break free from their covalent bonds and become mobile charge carriers. This leaves behind positively charged holes in the lattice. The generation of these electron-hole pairs enables electrical conduction in intrinsic semiconductors.
The number of electron-hole pairs, and thus the conductivity, increases exponentially with increasing temperature in intrinsic semiconductors. But even at room temperature, the number of charge carriers is relatively low compared to metals. This is why the conductivity of intrinsic semiconductors lies between conductors and insulators.
What is an Extrinsic Semiconductor? – Definition and Explanation
An extrinsic semiconductor is a semiconductor that has been intentionally mixed with controlled amounts of impurities in a process called doping. The added impurities, called dopants, donate extra electrons or holes, greatly increasing the number of charge carriers and the electrical conductivity compared to an intrinsic semiconductor.
Silicon and germanium are commonly used as base intrinsic semiconductors which are then doped to make extrinsic semiconductors. The two types of extrinsic semiconductors are n-type and p-type, depending on the dopant used.
Difference between Intrinsic and Extrinsic Semiconductors – Pointwise
Here are some differences between intrinsic and extrinsic semiconductors:
- Conductivity: Extrinsic semiconductors have much higher electrical conductivity than intrinsic ones due to doping.
- Charge Carriers: In intrinsic semiconductors, charge carriers are from thermal generation of electron-hole pairs. Extrinsic semiconductors have additional electrons or holes from dopant atoms.
- Dopants: Intrinsic semiconductors do not contain any dopants, while extrinsic semiconductors are intentionally doped.
- Temperature Dependence: Conductivity of intrinsic semiconductors depends exponentially on temperature. Doped extrinsic semiconductors have relatively temperature-independent conductivity.
- Band Structure: Doping causes the Fermi energy level to move into the conduction or valence band in extrinsic semiconductors. Intrinsic semiconductor Fermi levels are in the middle of the band gap.
- Control: It is easy to control the conductivity and other properties of extrinsic semiconductors by carefully adjusting the doping levels. Intrinsic semiconductor conductivity depends on the material and temperature only.
Doping in Extrinsic Semiconductors
Doping is the key process that makes extrinsic semiconductors so useful in electronics. It works by intentionally introducing impurity atoms into the intrinsic semiconductor crystal lattice during manufacturing. The impurity atoms take positions in the lattice, replacing atoms of the intrinsic semiconductor material. The impurity atoms have a different number of valence electrons than the intrinsic atoms they replace, altering the electronic properties.
Silicon, for example, has 4 valence electrons. If a silicon atom is replaced by a phosphorus atom (which has 5 valence electrons), the extra electron is only loosely bound and can become a mobile charge carrier. This allows phosphorus to act as a donor dopant.
On the other hand, boron only has 3 valence electrons. Replacing a silicon atom with a boron atom leaves a vacancy that can accept an electron, creating a hole. Therefore, boron serves as an acceptor dopant.
The overall effect is that doping adds extra charge carriers beyond what is thermally generated in the intrinsic material. This dramatically increases electrical conductivity. The conductivity can be precisely controlled by the amount and type of dopant used.
Types of Extrinsic Semiconductors Based on Doping
There are two types of extrinsic semiconductors classified by the dopants used:
N-type semiconductors are doped with donor impurities like phosphorus or arsenic. The donor atoms have more valence electrons than the semiconductor base material. The extra electrons are only loosely bound and can become mobile charge carriers.
Since the charge carriers are negative electrons, n-type semiconductors have a net negative charge from the excess electrons. The electrons are the majority carriers, while holes are the minority carriers in n-type semiconductors.
P-type semiconductors are doped with acceptor impurities like boron or gallium. These acceptor atoms have fewer valence electrons than the intrinsic semiconductor lattice. This creates holes that can accept extra electrons and become charge carriers.
The holes in p-type semiconductors carry a net positive charge. Holes are the majority charge carriers, while electrons are the minority carriers in p-type semiconductors.
Electronic Structure of Extrinsic Semiconductors
Doping introduces impurity energy levels close to the conduction and valence bands in extrinsic semiconductors. These additional energy levels influence the Fermi levels and band structures.
In intrinsic semiconductors, the Fermi level lies roughly in the middle of the band gap between the conduction and valence bands. Doping causes the Fermi level to split and move closer to either the conduction or valence band edge.
In n-type semiconductors, donor levels are created near the conduction band. At moderate doping, the Fermi level shifts into the lower part of the conduction band. In heavily doped n-type semiconductors, the Fermi level can move through the conduction band.
In p-type semiconductors, acceptor levels form near the top of the valence band. The Fermi level shifts toward the valence band edge with increased doping. At high doping, the Fermi level can pass through the valence band.
This splitting of the Fermi level is very important, as it makes the Fermi level and carrier concentrations depend much less on temperature in extrinsic versus intrinsic semiconductors.
Key Differences Between Intrinsic and Extrinsic Semiconductors
To summarize, here are some of the most important differences between intrinsic and extrinsic semiconductors:
- Conductivity – Extrinsic semiconductors have higher conductivity due to doping. Intrinsic semiconductor conductivity depends only on temperature.
- Charge Carriers – Extrinsic semiconductors have extra electrons or holes from doping. Intrinsic semiconductor charge carriers come from electron-hole generation.
- Dopants – Extrinsic semiconductors contain intentional dopant impurities. Intrinsic semiconductors have no dopants.
- Temperature dependence – Intrinsic semiconductor conductivity varies exponentially with temperature. Extrinsic semiconductors have more stable conductivity vs. temperature.
- Band structure – Doping causes splitting of the Fermi level in extrinsic semiconductors. The intrinsic semiconductor Fermi level is in the middle of the band gap.
- Control – Extrinsic semiconductor properties can be precisely controlled by doping levels. Intrinsic semiconductor properties depend on the material and temperature.
Characteristics of Extrinsic Semiconductors
Extrinsic semiconductors have several unique properties thanks to doping:
- Higher conductivity – More charge carriers from doping increase conductivity. N-type semiconductors have negative charge carriers from donor electrons. P-type semiconductors have positively charged holes from acceptors.
- Controllable properties – Conductivity, charge carrier density, etc. can be adjusted by the doping level and type. Heavier doping results in higher conductivity.
- Low temperature dependence – Doping provides charge carriers not reliant on thermal generation, so extrinsic semiconductor conductivity varies less with temperature.
- Internal electric fields – The asymmetric donor and acceptor doping in n-type and p-type semiconductors produces internal electric fields that can drive charges one way.
- Junctions – Joining n-type and p-type semiconductors allows control of current flow across p-n junctions, a key feature of semiconductor electronics.
Applications of Extrinsic Semiconductors
The unique properties of extrinsic semiconductors make them ideal for many important practical applications:
- Diodes – p-n junction diodes use directional electric fields to allow current to flow in only one direction. Diodes are fundamental to semiconductor devices.
- Transistors – Bipolar junction transistors (BJTs) use p-n junctions to amplify and switch electrical signals and power in computers, radios, etc.
- LEDs – Light-emitting diodes use p-n junctions to convert electricity into light for displays, lighting, and more.
- Solar Cells – Photovoltaic solar cells absorb light in the p-n junction to generate electricity from sunlight.
- Rectifiers – Rectifier diodes convert alternating current (AC) into direct current (DC) by blocking reverse biased current flow.
- Logic Gates – Transistors wired into logic gates like AND, OR, and NOT form the basic building blocks of digital logic.
Examples of Extrinsic Semiconductor Materials and Uses
Some of the most common extrinsic semiconductor materials used in electronics include:
- Silicon – One of the most widely used semiconductors on its own and in alloys. Doped silicon is ubiquitous in integrated circuits, solar cells, rectifiers, sensors, and more.
- Germanium – An early transistor material and still used in some diodes and transistors today. Lower bandgap than silicon.
- Gallium Arsenide – Important for LEDs, lasers, solar cells and ultra-high frequency electronics. Higher electron mobility than silicon.
- Silicon Carbide – Withstands high temperatures and powers. Used for blue LEDs, power electronics, and detectors in harsh environments.
- Gallium Nitride – Essential for bright white LED lighting, violet lasers, and high-power, high-frequency devices.
- Indium Phosphide – Used for high-speed logic, amplifiers and photonic devices like fiber optic cables.
Distinguish Between Intrinsic and Extrinsic Semiconductor Conclusion
Intrinsic and extrinsic are the two main classifications of semiconductors. While intrinsic semiconductors rely on thermal generation of charge carriers, extrinsic semiconductors use doping to dramatically increase the number of electrons and holes. This allows extrinsic semiconductors to have higher, controlled conductivity.
Analyzing the intrinsic vs. extrinsic semiconductor band structures gives insight into how dopants enable unique electronic properties. Overall, extrinsic semiconductor development has enabled modern solid-state electronics ranging from transistors to solar cells and LEDs. Understanding the physics and applications of these remarkable materials is key to advancing future electronics. For more information click hear byjus.
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Distinguish Between Intrinsic and Extrinsic Semiconductor
- How do intrinsic semiconductors generate electron-hole pairs?In intrinsic semiconductors, electrons gain enough thermal energy to break their covalent bonds and become mobile charge carriers, leaving behind positively charged holes. The higher the temperature, the more electron-hole pairs are thermally generated this way.
- Why are N-type semiconductors good conductors?N-type semiconductors are doped with impurities that donate extra electrons as charge carriers. The electrons from donor atoms make n-type semiconductors conductive. More doping provides more electrons and higher conductivity.
- How do semiconductors differ from conductors and insulators?Conductors have very high conductivity, while insulators have extremely low conductivity. Semiconductors fall between conductors and insulators, with moderate conductivity from electron-hole pairs or doping. Only semiconductors can have conductivity precisely tailored by doping.
- Why are extrinsic semiconductors better than intrinsic ones?Extrinsic semiconductors have higher, controlled conductivity from doping. Tunable n-type and p-type doping enables unique electronic devices. Extrinsic semiconductors also have temperature-independent conductivity unlike intrinsic materials. Overall, extrinsic semiconductors are more versatile and adaptable.