Look around you; semiconductors are everywhere

Introduction

If you are reading this blog post, it is thanks to the remarkable role that semiconductors play in modern technology. Semiconductors are materials with electrical conductivity that lie between conductors and insulators. This effect occurs naturally in certain elements near the so-called “metalloid staircase” on the periodic table. Some pure elements, including silicon and germanium, display semiconductor properties, while other compounds, like gallium arsenide, also display such properties.

In conductive materials, electrical current occurs with the movement of electrons. Semiconductors, however, allow the partial flow of electrons, but this requires specific conditions to be triggered. In this type of material, electrons can be in one of two states: either in the valence band or the conduction band. Only the electrons in the conduction band can travel, generating the electrical current. For the electrical current to occur, electrons need to move from the valence band need to transition, a process that requires energy input. The amount of energy required for this transition determines the susceptibility of electrons to be excited and, consequently, the electrical conductivity of the semiconductor. Additionally, when an electron has moved from the valence to the conduction band, the “hole” (or empty state) left behind allows for conductivity¹.

Some materials exhibit intrinsic semiconductor properties. In this case, the number of electrons and holes is equal. The conduction of electrical current is purely linked to electron excitation across the band gap. The holes left by the displaced electrons can be filled with other electrons, creating new holes that will travel across the material in the opposite direction to the electrons. At normal conditions, the electrons can transition through the gap, resulting in the semiconductor being able to allow electric current. However, semiconductors can also be artificially produced through a process called doping, which involves adding impure atoms to a non-semiconductor material to create extrinsic semiconductors. These dopant atoms provide mobile electrons into the crystal lattice. There are two types of doping atoms: electron donors, which supply electrons (n-type semiconductors), or electron acceptors, which accept electrons, creating holes (p-type semiconductors).

ISO-BTC

ISO-BTC Battery Testing Equipment for the Laboratory

Semiconductor Applications

Silicon is one of the most used semiconductor elements, widely used as the base material for microchips – which also receive the name integrated circuit or monolithic integrated circuit. Silicon has the advantage of being the second most abundant element on earth, just after oxygen. It can be doped using other impure atoms, such as phosphorus or boron, affecting its electrical properties. Microchips are used in almost every single one of the modern electronic devices. There are two main types of microchips: logic chips and memory chips. The former is capable of processing the information that the electronic device requires to complete their task. Memory chips, on the other hand, are capable of storing information. Miniaturization has allowed the production of embedded systems, which are miniature computers that are a part of larger devices, including mobile phones, consoles, computers, and kitchen appliances.

Transistors are another ubiquitous application of semiconductors. In this case, there are three layers of semiconductors: either an n-type semiconductor layer between two p-types (positive-negative-positive configuration) or p-type between two n-types (negative-positive-negative configuration). The inner layer acts as the control electrode, where small changes in current or voltage can trigger a large and rapid change in the current passing through the transistor. Transistors are fundamental in forming logic gates, the building blocks of modern computing, and have long been used to amplify weak electronic signals, such as those in FM radio.

Solar photovoltaic cells are also powered by semiconductors. In these cells, photons from sunlight excite electrons, transferring energy and allowing them to move from the valence band to the conduction band. The movement of electrons creates an electric current that can be harnessed and used. Different materials have different band gaps, and as such, the material used in the design of the photovoltaic cells will determine which wavelengths will be absorbed and converted into electricity.

Semiconductors are everywhere If photovoltaic cells are designed to absorb and transform light into electricity, LEDs do the complete opposite. Light-emitting diodes are composed of two types of semiconductors: a p-type and an n-type. When the electric current is applied, electrons from the n-type semiconductor migrate towards the p-type. Simultaneously, the holes from the p-type semiconductor start moving toward the n-type part of the circuit. This results in a process known as recombination and the difference between the energetic levels is released as light. The high efficiency of LEDs has replaced traditional incandescent and fluorescent lights in homes, streets, and vehicles. The semiconducting materials from which the LED is made determine the color of the light emitted.

Semiconductors in the present and future

As we can see, semiconductors are ubiquitous in our lives. They are silent enablers behind much of the technology that surrounds us. From microchips powering our mobile phones to the LEDs lighting our homes and the solar cells that we use in the attempt to create a greener world, semiconductors are at their core.

However, we cannot take semiconductors for granted, even though silicon is so abundant. The Chip Shortage between 2020 and 2023 highlighted our dependence on these products. The scarcity of microchips led to a surge in prices, long queues to purchase them, and reselling among consumers and manufacturers. The lead times reached a peak of more than 22 weeks, compared to just over 12 weeks in February 2020. Research and development are, therefore, fundamental to making us more resilient and diminishing potential issues.

As technology continues to evolve, the role of semiconductors will only grow, driving further innovation and shaping the future of electronics and energy. Understanding the electrical properties behind these materials not only highlights their importance but also opens the door to unexpected possibilities for future applications