What are semiconductors?
These are materials with a double behavior and are basic for the electronic age in which we live.
Did you know that without semiconductors life would not be as you know it? These modest materials play a fundamental role in shaping our modern technological reality. From the computer you use every day to the mobile devices in your pocket, semiconductors are the quiet heroes making the digital revolution possible .
Semiconductors are much more than just materials; They are the foundations on which modern electronics are built. Its role is not limited to just conducting electrical current, but its unique behavior opens the door to a wide range of technological applications that have radically transformed society. What makes semiconductors so special? What are the characteristics that distinguish them and why are they essential in the world of electronics? In this article we will explore the fascinating world of semiconductors, discovering what characterizes them and why they are so essential in contemporary electronics.
The dual nature of semiconductors
Semiconductors are not simply conductors or insulators; They are creatures of electrical duality. Unlike conductors, they do not allow unrestricted electrical flow, and unlike insulators, they do not completely block the passage of current. They are like the wild card in the electrical game, capable of changing their conductivity at will.
That is, a semiconductor allows the passage of electric current when certain conditions are met, while preventing the passage of said current under other conditions. The most fascinating thing about semiconductors is their ability to adapt. Imagine having a switch that controls electrical conductivity: that’s exactly what these materials do. Its flexibility to adjust its driving ability is the cornerstone of modern electronics .
The importance of impurities
In the world of semiconductors , duality manifests itself not only in its general behavior, but also in two specific categories: intrinsic semiconductors and extrinsic semiconductors .
Intrinsic semiconductors , such as silicon or germanium, form crystals with tetrahedral structures, similar to that of carbon, through covalent bonds between atoms. At room temperature, some electrons can absorb the energy necessary to jump to the conduction band, leaving a gap in the valence band. This dynamic balance between the creation of electron-hole pairs and recombination keeps the concentration of electrons and holes constant.
If a small percentage of impurities, trivalent or pentavalent elements, are added to an intrinsic semiconductor, it becomes an extrinsic or doped semiconductor . These impurities, being part of the crystalline structure, replace the original atoms . If trivalent atoms are added, the semiconductor is called N-type; If they are pentavalent atoms, it is called P type.
Electrons and holes
When we talk about an N-type semiconductor , we are referring to a material that has been doped with donor atoms , such as phosphorus or arsenic . These donor atoms have more electrons in their valence shell than the original semiconductor, and by incorporating them into the semiconductor’s crystal lattice, they contribute additional electrons to the system .
Let’s think for example of silicon , which has four electrons in its valence shell. We introduce phosphorus atoms, which have five valence electrons, instead of silicon into the crystal structure. The phosphorus atom covalently bonds with adjacent silicon atoms, and the unbonded fifth electron becomes a “free electron.” This extra electron contributes to the formation of an abundance of negatively charged electrons.
N-type doping seeks, therefore, to create an excess of electrons in the material, converting them into majority carriers. These free electrons are essential for the efficient conduction of electrical current in semiconductor devices. Thus, the N-type semiconductor becomes a valuable tool for building electronic components such as transistors, where the mobility of electrons is crucial.
In contrast, the P-type semiconductor is obtained by doping with acceptor atoms , such as aluminum or gallium. These acceptor atoms have fewer electrons in their valence shell than the original semiconductor, and when introduced into the crystal lattice, they generate “holes” instead of electrons .
Taking again the example of silicon, which has four electrons in its valence shell, let us now imagine aluminum atoms, which have three valence electrons, occupying places in the crystal structure. By forming covalent bonds with adjacent silicon atoms, a gap is created in the valence band, since the aluminum atom does not contribute a fourth electron. These holes behave as positive charge carriers.
P-type doping aims to generate an abundance of holes, turning them into majority carriers in the material. These holes, along with the minority electrons, are essential for the conduction of electric current in specific directions. P-type semiconductors are essential for building devices such as diodes, where hole mobility plays a crucial role in controlling electrical flow.
Transistors: a team effort
Transistors are built using the intelligent combination of N- and P-type semiconductors, taking advantage of the unique properties of each. At the heart of a transistor, we find the famous pn junction, where the P-type region is adjacent to the N-type region. This strategic junction allows controlling the flow of current between both regions, acting as a kind of electrical switch. When a voltage is applied to the P-type region, the holes, the majority carriers in this type of semiconductor, move towards the pn junction. Simultaneously, in the N-type region, the electrons, the majority carriers in this case, move towards the junction. This displacement of carriers creates a depletion zone, a kind of electrical barrier, which regulates the current between the two regions .
This voltage-controlled modulation at the p-n junction allows the transistor to act as an electrical signal amplifier . Small variations in the applied voltage can generate significant changes in the current between the N- and P-type regions, amplifying the original signal. This property is essential in applications such as audio amplification and data transmission. In addition to their role in amplification, transistors are also used as electronically controlled switches. In logic circuits, the presence or absence of current at the p-n junction can represent logic states 0 and 1, forming the basis of digital electronics and modern computing.
Diode: order is important
A diode is a fundamental electronic component that possesses semiconductor properties and allows the unidirectional flow of electrical current . Its basic structure consists of two regions, one P-type and one N-type, forming a pn junction. In the P-type region, holes are the majority carriers, while in the N-type region, electrons are the majority carriers.
The primary function of a diode lies in its ability to allow current to flow in one direction , known as the forward direction, and block flow in the opposite direction, called the reverse direction. This unidirectional behavior is essential in various electronic applications.
When a positive voltage is applied in the forward direction, electrons in the N-type region are attracted to the holes in the P-type region, allowing current to flow through the diode. On the other hand, in the reverse direction, the potential barrier created by the pn junction is strengthened, making the passage of current significantly more difficult.
This property of allowing current flow in only one direction makes diodes crucial in rectifier circuits , converting alternating current to direct current, and in protection against polarity reversal. They are also used in applications such as power supplies, signal modulation and logic circuits, highlighting their versatility in the design of electronic circuits.
Diodes find a wide variety of applications in the electronic field, and one of the most notable is in light-emitting diode (LED) technology. LEDs are semiconductor devices that emit light when an electric current passes through them in the direct direction. This ability to convert electrical energy directly into light makes LEDs energy efficient and versatile in various applications.
From Nobel to AI
The history of semiconductors is marked by a revolution in the electronics industry that occurred since the mid-20th century. These materials replaced traditional electrical tubes , offering significant improvements in size, power consumption, cost, durability and reliability. This transformation revolutionized electronics and computing.
The term “semiconductor” was coined by Alessandro Volta in 1782 , but it was in 1833 that Michael Faraday made the first documented observation of the effect of semiconductors. Edwin Herbert Hall discovered the Hall effect in 1878, a key phenomenon in the understanding of semiconductors. At the beginning of the 20th century, John Ambrose Fleming developed the vacuum diode and Lee de Forest invented the triode, the first electronic devices.
In the following decades, different materials were experimented with, from galena crystal to selenium rectifiers and copper oxide. During the 1920s and 1940s, the tetrode and pentode were developed, and explanatory theories based on quantum mechanics were formulated. In 1923, Walter H. Schottky contributed to the theoretical study of semiconductors .
The most notable milestone occurred in 1947 when John Bardeen, Walter Brattain and William Shockley created the first transistor, made of germanium . This achievement marked a significant change in the control, amplification and generation of electronic signals, leading them to receive the Nobel Prize in 1956 for the aforementioned discovery. Since then, semiconductors have been the foundation of modern technology, enabling extraordinary advances in electronics and computing. Even the artificial intelligence (AI) that is so popular today would be impossible without semiconductors.
The relationship between semiconductors and artificial intelligence (AI) is critical to the development and operation of advanced machine learning systems . Processors specialized in AI tasks, such as graphics processing units (GPUs) and tensor processors, rely on semiconductors to efficiently execute complex matrix operations, essential in training and running deep learning models.
Additionally, hardware accelerators designed specifically for AI tasks, such as Tensor Processing Units (TPUs) and Machine Learning Integrated Circuits (ASICs), rely on advanced semiconductor technologies to improve model performance and efficiency. of AI. These hardware advancements also include neural processing units (NPUs), which play a crucial role in accelerated data processing for artificial intelligence applications.
High-performance memory used in artificial intelligence systems, such as RAM and flash memory, is built on the basis of semiconductor technologies. These components are vital for providing fast access to large data sets, a critical need in the field of deep learning.
In addition, the convergence of artificial intelligence with the Internet of Things (IoT) relies on semiconductors for the creation of data capture devices, such as cameras and sensors. These devices, by using electronic components based on semiconductors, convert physical signals into digital data, allowing the entry of information into artificial intelligence systems.