Semiconductors are exactly what their name implies. Occupying a separate category between conductors and insulators, their conductivity can be precisely controlled. Conductivity is widely used to discern each material and its distinct characteristics, but the differences among the three types of materials arise from a deeper root than simply their conductivities; they come from the number of free electrons present in the material. An elementary, broad approach to examining these free electrons is to refer to the periodic table. Using just the arrangement of the periods and groups, elements can be classified into metals, nonmetals, or metalloids, and can be further distinguished by their numbers of valence electrons. Metalloids, especially silicon, are valuable in the semiconductor industry for their unique properties that have led them to shape the foundation of modern electronics.
Perhaps a more sophisticated approach in studying free electrons is to use energy band diagrams, which establish the energy levels of the electrons in the material. Due to their wave-like nature, electrons are restricted to discrete energy levels and can only move from one specific energy state to another. A basic energy band diagram consists of a conduction band at the top and a valence band at the bottom. The conduction band holds the electrons that have escaped from their original atoms, while the valence band holds the valence electrons of the atom, otherwise known as the electrons with the highest energy level. Between the two bands lies a band gap, which reflects the amount of energy an electron needs to travel from the valence band to the conduction band. Insulators have large band gaps, which suggest that, at normal temperatures, no electrons can rise to the conduction band. Conductors,
in contrast, have no band gap at all, so the valence electrons are essentially free to move to the conduction band. Fortunately, semiconductors have higher mobilities at room temperature and higher temperatures; they have a band gap small enough that electron excitations such as thermal energy can bridge the gap and allow some electrons to reach the conduction band.
So what does this intricate concept in quantum physics reveal about the nature of semiconductors? Because their conductivities can be controlled by electric currents, electric fields, and doping–the process of introducing impurities into a perfectly pure crystal–semiconductors can both allow and resist the flow of electricity. This special property makes them useful as a controllable switch in myriad modern electronic devices. With just a small amount of voltage, engineers can generate more voltage or current by using semiconductors. As rudimentary components of ubiquitous devices such as televisions, computers, and cellphones, they are so prevalent in our everyday lives that it would be more difficult to find an electrical product that does not have semiconductors than it would be to find one that does. From refined, expensive medical appliances to the simplest amplifier or the most inexpensive transistor radio, these tiny chips play a paramount role in advancing technology. More specifically, silicon, one of the most important semiconductors today due to its low defect rate, is commonly used to fabricate computer chips, standing out among other materials because of its superior physical and technological properties.
Dating back to some of the most advanced electronics during World War II and continuing forwards to 64-bit processors and the 14nm fabrication node, semiconductor technology is surely becoming a part and parcel of our lives. From 1940 onwards, silicon, a mechanically strong element with reasonable electrical properties, has been the dominant semiconductor material. If the primary necessity of semiconductors was still for computer chips, diodes, and transistors, silicon would continue to be the ideal material to use. Yet that is not the case anymore, as there has been an increasing demand for alternative materials that have a higher intrinsic mobility than that of silicon. Because silicon cannot efficiently convert light into an electrical signal and vice versa, researchers have always been on the lookout to find alternative materials that work well with light. This ongoing search for new, organic semiconductors challenges the status quo of the technology world, leading the pathway for heightened functionality in applications.
Reputed for their considerable contributions to material science, semiconductors have transformed the way we work, communicate, treat illnesses, and entertain ourselves. Not only are they crucial in transistors (thin film or field-effect), but they are also a very affordable means of processing, storing, and transmitting electricity. Companies including Intel, Samsung Electronics, and Qualcomm are looking forward to developing advanced semiconductors appropriate for the “Internet of Things” (IoT). Simply put, the IoT is an expansive network of connectivity, which permits any device with an on and off switch to connect to the Internet or to each other. Before the IoT first became popular in 1999, the concept was referred to as “Ubiquitous Computing” or “UbiComp.” Though the term seems rather awkward, it effectively reflects the ever-growing trend of bringing former non-computational devices into the fold of computation. Recent news of graphene’s stable band gap, the potential of diamond as a semiconductor, and the emergence of new 3D materials have inspired countless material scientists and electrical engineers to continue their works to replace conventional Si-based electronics. Along with other countries, the United States and Korea are constantly developing a new technological platform through investments, collaboration, and scientific research, keeping in mind that the future of semiconductors is open to improvement in terms of biocompatibility, storage capacity, and augmented (virtual) reality.
In reality, there aren’t many things that function better as they become smaller and smaller. But semiconductors are an exception: the smaller they are, the more storage and the higher performance they have. As more and more improvements occur, chips will get smaller and smaller, but the industry will only get bigger.