Semiconductor Physics and Technology

The fabrication of these devices relies on advanced manufacturing techniques, including crystal growth, photolithographic pattern transfer, and precision doping. 

A single semiconductor chip has as many transistors as all of the stones in the Great Pyramid in Giza, and today there are more than 100 billion integrated circuits in daily use around the world - that’s equal to the number of stars in our corner of the Milky Way galaxy.

Semiconductors have entered our everyday life to such a degree that the notion of a “silicon age” has been employed. Silicon is in fact the most important material as far as commercial applications of semiconductors are concerned. However, while silicon satisfies most of our current needs for electronics, it is only of limited use for optoelectronic applications. 

Semiconductor lasers, which are at the heart of compact disc players (present in most households), laser printers, and light modulators, the key to today’s telecommunication systems, require a direct band gap. Hence, many other semiconductor materials are subjects of current interest. 

Moreover, today’s scientists are no longer satisfied with the variety of bulk materials provided by nature, but have become artists who design semiconductor heterostructures and mesos-copic semiconductor devices corresponding to their needs and interests. This often results in surprising and quite remarkable material properties. 

The paragraphs above highlight the revolutionary impact of semiconductors on modern technology, the limitations of silicon in optoelectronics, and the shift towards engineered materials such as heterostructures, which are being used to manufacture advanced optical and quantum devices.

1. The Silicon Baseline & Its Limits:

• Silicon Supremacy: Silicon dominates commercial computing and electronics due to its abundance, thermal stability, and ideal electrical properties. Modern microchips can hold billions of transistors in an area smaller than a fingernail.
• The Optoelectronic Hurdle: While exceptional for digital logic, silicon has an indirect band gap. This means that when electrons release energy, they primarily emit heat instead of light, making it highly inefficient for lasers, fiber optics, or LEDs. 

2. The Need for Direct Band Gap Materials:

• How They Work: Unlike silicon, materials with a direct band gap (such as Gallium Arsenide or Indium Phosphide) align electron momentum between energy bands. When electrons transition, they efficiently convert their energy directly into light. 
• Real-World Applications: Direct band gap semiconductors power technologies we rely on daily, including compact disc lasers, laser printers, telecommunication light modulators, and optoelectronic sensors.

3. The Shift to Engineered Heterostructures: 

To bypass the limitations of natural bulk materials, scientists now engage in band gap engineering by layering different semiconductor materials on the nanoscale. 

• Heterojunctions: By joining two dissimilar semiconductors, scientists create abrupt interfaces that force electrons to behave in custom ways. 
• Mesoscopic & Artificial Devices: This allows for custom material properties. Scientists can now build quantum wells, superlattices, and artificial materials tailored for specific wavelengths, ultra-fast speeds, or high-power efficiencies unachievable in nature. 

MOSFET stands for Metal Oxide Silicon Field Effect Transistor or Metal Oxide Semiconductor Field Effect Transistor. This is also called as IGFET meaning Insulated Gate Field Effect Transistor. The FET is operated in both depletion and enhancement modes of operation.

The MOSFET transistor is a semiconductor device that is widely used for switching purposes and for the amplification of electronic signals in electronic devices. A MOSFET is either a core or integrated circuit where it is designed and fabricated in a single chip because the device is available in very small sizes. The introduction of the MOSFET device has brought a change in the domain of switching in electronics.

The construction of a MOSFET is a bit similar to the FET. An oxide layer is deposited on the substrate to which the gate terminal is connected. This oxide layer acts as an insulator (sio2 insulates from the substrate), and hence the MOSFET has another name as IGFET. In the construction of MOSFET, a lightly doped substrate, is diffused with a heavily doped region. Depending upon the substrate used, they are called as P-type and N-type MOSFETs.

The voltage at gate controls the operation of the MOSFET. In this case, both positive and negative voltages can be applied on the gate as it is insulated from the channel. With negative gate bias voltage, it acts as depletion MOSFET while with positive gate bias voltage it acts as an Enhancement MOSFET.

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A specific semiconductor process has specific rules on the minimum size and spacing for features on each layer of the chip. Often a newer semiconductor processes has smaller minimum sizes and tighter spacing which allow a simple die shrink to reduce costs and improve performance partly due to an increase in transistor density (number of transistors per square millimeter). 

Early semiconductor processes had arbitrary names such as HMOS III, CHMOS V; later ones are referred to by size such as 90 nm process. 

By industry standard, each generation of the semiconductor manufacturing process, also known as technology node or process node, is designated by the process’ minimum feature size. Technology nodes, also known as "process technologies" or simply "nodes", are typically indicated by the size in nanometers (or historically micrometers) of the process' transistor gate length. 

However, this has not been the case since 1994. Initially transistor gate length was smaller than what the process node name (e.g. 350 nm node) suggested, however this trend reversed in 2009. 

The nanometers used to name process nodes has become more of a marketing term that has no relation with actual feature sizes nor transistor density (number of transistors per square millimeter). For example, Intel's 10 nm process actually has features (the tips of FinFET fins) with a width of 7 nm, Intel's 10 nm process is similar in transistor density to TSMC's 7 nm processes, while GlobalFoundries' 12 and 14 nm processes have similar feature sizes.

1. 1971 - 2021

• 10 µm – 1971
• 6 µm – 1974
• 3 µm – 1977
• 1.5 µm – 1981
• 1 µm – 1984
• 800 nm – 1987
• 600 nm – 1990
• 350 nm – 1993
• 250 nm – 1996
• 180 nm – 1999
• 130 nm – 2001
• 90 nm – 2003
• 65 nm – 2005
• 45 nm – 2007
• 32 nm – 2009
• 22 nm – 2012
• 14 nm – 2014
• 10 nm – 2016
• 7 nm – 2018
• 5 nm – 2020

2. Post-2021

• 3 nm – ~2022
• 2 nm – >2023

The semiconductor industry’s modern manufacturing landscape (up to 2026) has evolved past traditional nanometer nodes, shifting its focus toward vertical stacking and advanced packaging.  

Current Industry Nodes (Post-2021):

• 3 nm Process: Reached volume production at major foundries like TSMC, powering high-performance computing and flagship mobile processors. 
• 2 nm Process: Pioneered by leading fabs utilizing innovative Gate-All-Around (GAA) nanosheet architectures to further improve transistor drive current and power efficiency.
• Angstrom Era: Major manufacturers have transitioned to naming conventions in the sub-nanometer scale (e.g., Intel's 18A process) to describe newer, high-density logic architectures. 
• 3D Stacking: Foundries are maximizing density by building devices vertically (e.g., CFETs), and utilizing backside power delivery to compensate for the diminishing returns of traditional shrinks.