Semiconductor Technology
Semiconductor technology revolutionizes electronic circuit fabrication by offering a unique approach. Unlike conventional methods that require external device integration, semiconductor technology allows for the creation of entire electronic circuits as a single, integrated unit. This integration occurs during the fabrication process, resulting in a monolithic semiconductor die commonly referred to as a “chip.” These chips, predominantly composed of silicon, serve as the foundation for a wide range of electronic applications.
Moreover, semiconductor technology is not limited to complete circuits; it can also construct discrete electronic devices, such as diodes, transistors, and thyristors. These devices, although seemingly single entities are often composed of multiple similar devices connected in parallel on a chip. This design allows for scalability and customization, making them suitable for applications involving high currents, particularly in power electronics. Protective circuitry, often hidden within the chip, enhances the performance and reliability of these devices.
The underlying physics of semiconductor materials is crucial to understanding their behavior. Semiconductors exhibit unique electrical characteristics. At room temperature, their electrical resistance is relatively high compared to conductive materials like metals. However, as the temperature rises, semiconductor conductivity experiences exponential growth, a property distinct from standard interconnects (metals).
Valence and Conduction Bands
In semiconductors, the primary charge carriers responsible for electrical current are electrons. These electrons must gain sufficient energy to move from the valence band to the conduction band to facilitate current conduction. The valence band contains valence electrons, while the conduction band permits free electron movement.
In contrast to metals, where valence and conduction bands are closely situated, semiconductors feature a band gap between these two bands. This band gap limits the number of electrons capable of transitioning to the conduction band. The manipulation of this band gap is essential for altering semiconductor conductivity.
Semiconductor Doping
Doping is a fundamental process in semiconductor technology. By introducing impurities into semiconductor materials, it is possible to modify their conductivity characteristics. Donors, which are five-valence impurity atoms, release an additional electron into the conduction band, resulting in n-doped semiconductor material with an excess of electrons. Conversely, acceptors, three-valence impurity atoms, accept valence electrons from neighboring atoms, creating additional holes in the valence band. This leads to p-doped semiconductor material with an excess of holes.
In n-doped regions, surplus electrons and holes tend to recombine, effectively neutralizing each other. Similarly, p-doped areas witness the recombination of extra holes and electrons.
Semiconductors are classified as n-conductive when donors predominate, leading to electron-driven current flow, with electrons being the majority carriers. In contrast, p-conductive semiconductors have an excess of acceptors, promoting hole-driven current flow, where holes are the majority carriers. This manipulation of charge carriers through doping allows for tailoring the electrical properties and behavior of semiconductor devices, making them highly adaptable for various applications in the realm of electronics.
What is the origin of the term “integrated circuit” (IC)?
The term “integrated circuit” originates from the fact that in semiconductor technology, all electronic devices and electrical connections are fully integrated into a monolithic semiconductor die.
How is the conductivity of semiconductors different from metals and insulators?
Semiconductors have intermediate conductivity, characterized by a band gap that lies between the large band gap of insulators and the overlap of valence and conduction bands in metals. The key property is that the conductivity of semiconductors increases exponentially with rising temperature.
What are the two types of impurity atoms used in doping semiconductors?
Two types of impurity atoms used in doping semiconductors are donors (five-valence impurity atoms) and acceptors (three-valence impurity atoms). Donors release electrons into the conduction band, while acceptors accept valence electrons from neighboring atoms.
What is the difference between n-doped and p-doped semiconductors?
N-doped semiconductors have surplus donors, and the current flow is primarily due to electrons (negative charge carriers). P-doped semiconductors have surplus acceptors, and current flow is mainly caused by holes (positive charge carriers). Majority carriers are the more abundant charge carriers, while minority carriers are the less abundant ones.
What is the most commonly used material in the semiconductor industry?
Silicon is the most widely used material in the semiconductor industry. It is preferred due to its excellent semiconductor properties and the ease of processing it into high-quality wafers.