EXTRINSIC SEMICONDUCTORS

Extrinsic semiconductors are formed by adding controlled amounts of impurity atoms (doping) to an intrinsic semiconductor crystal. The introduction of these impurities, changes the conductivity of the semiconductor, enabling it to be used in a wide range of applications.

There are two main types of extrinsic semiconductors and they are; N and P type extrinsic semiconductors.

The N type extrinsic semiconductor is created by doping or adding impurities to an intrinsic semiconductor, typically silicon or germanium, group IV elements with pentavalent impurities or atoms from group V of the periodic table. The common dopants used are usually phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) etc.

The P type extrinsic semiconductor is created by doping an intrinsic semiconductor with trivalent impurities or atoms from group III of the periodic table. The common dopant used are , boron (B), aluminum (Al), gallium (Ga), indium (In) etc.

The advantages of extrinsic semiconductors are; doping introduces a large number of additional charge carriers (electrons in N type, holes in P type) boosting conductivity by orders of magnitude compared to intrinsic semiconductor s or materials, making extrinsic semiconductors practically useful for real circuit applications. The behavior of extrinsic semiconductors can be predicted by adjusting the type and concentration of the dopant or impurities, thus enabling precise control of conductivity, carrier type, threshold voltage and switching behavior, that is impossible with intrinsic semiconductors. Combining N type and P type semiconductors creates the P-N junction, the fundamental building block of diodes, transistors, solar cells and LED. While still temperature dependent, extrinsic semiconductors maintain more stable conductivity over a wider practical temperature range than intrinsic semiconductors. Precise doping enable miniaturization and integration, thereby allowing extremely small, densely packed device structures, which is the basis of modern integrated circuits with billions of transistors. Extrinsic semiconductors exhibit a wide range of engineered behaviors thus enabling the creation of custom electrical, optical and thermal characteristics for specific applications.

The disadvantages of extrinsic semiconductors are; achieving precise, uniform doping requires advanced techniques like ion implantation, diffusion and epitaxial growth, all requiring clean room environments and expensive equipment. Extrinsic semiconductors are very sensitive to contamination and process errors, which can significantly affect device performance, yield and reliability. Extrinsic semiconductors are susceptible to performance degradation at high temperatures. Also some high performance dopants or compound semiconductor combinations involve toxic or rare elements (e.g. arsenic, cadmium, indium, gallium etc.) which may not only raise cost but also create safety and supply chain concerns.

The applications of extrinsic semiconductors are as follows; extrinsic semiconductors such as diodes are used to enable rectification (AC to Dc conversion), voltage regulation using zener diodes and signal demodulation. Extrinsic semiconductors such as transistors (BJTs,MOSFETs, FETs etc) which is the core active components for amplification and switching in nearly all electronic devices. Extrinsic semiconductors such as integrated circuits (ICs) are used in CPU, memory chips (RAM, ROM, FLASH etc.), microcontrollers which is built using millions to billions of precisely doped transistor structures. Extrinsic semiconductors are used in devices such as solar cells and photovoltaic which converts light into electrical energy. Extrinsic semiconductors are used in devices such as LEDs and LASER diodes, which releases energy as light. Extrinsic semiconductors are used in power electronics for the design and manufacture of rectifiers, inverters, voltage regulators ang power transistors in motor drives, EV charging and renewable energy systems. Extrinsic semiconductors are used in sensors types such as hall effect sensors (magnetic field detection), photodiodes (light detection), thermistors with engineered doping, gas sensors etc. extrinsic semiconductors are used in RF and microwave devices, which are heavily doped compound semiconductors (GaAs, InP etc) used in high frequency amplifiers, mobile communication and radar systems. Extrinsic semiconductors are used in memory and storage devices, which are doped semiconductors structure, the basis of flash memory cells, DRAM and emerging non-volatile memory technologies.

The future of extrinsic semiconductors is based on the advances and development of the following technologies; extrinsic semiconductors will continue to play a crucial role in the development of IoT devices, high frequency devices for 5G and 6G communication, electric vehicles and other electronics and electrical systems, such as robotics, motor control etc.  Extrinsic semiconductors will be the foundation of quantum computing devices such as quantum processors and quantum memory devices. Development of new materials and technologies such as grapheme, Nano tubes and 3D materials will be used in the future to create advanced extrinsic semiconductors. Extrinsic semiconductors will be integrated with other technologies such as Nano technology, bio technology and cognitive science to create new classes of devices and systems.

 

SOURCES:

• Semiconductor device physics and technology by S.M Sze.
• Extrinsic semiconductors: A review of the literature by J.M Philips.
• Semiconductor materials and devices by D.A Neemen.
• Introduction to semiconductor technology by C.Y Chang and S.M Sze.
• Semiconductors: A modern material perspective by P.Y Yu and M. Cardona.