What Are Elemental Semiconductors?

Elemental semiconductors are semiconductor materials composed of a single chemical element rather than a compound of two or more elements. Silicon and germanium, both members of Group IV of the periodic table, are the archetypal examples, with silicon occupying the dominant role in the global microelectronics industry. These materials exhibit electrical conductivity that falls between that of a metal and an insulator and can be precisely controlled by introducing small concentrations of dopant atoms, making them the foundation of transistors, diodes, and integrated circuits.

The properties of elemental semiconductors derive from the covalent bonding of their atoms in a diamond cubic crystal lattice, a face-centered cubic structure with a two-atom basis in which each atom forms four tetrahedral bonds with its nearest neighbors. This lattice geometry governs the electronic band structure and thereby the optical, electrical, and mechanical properties of the material.

Silicon

Silicon is the most widely used semiconductor material in history, forming the basis for virtually all modern integrated circuits, solar cells, and power devices. It has an indirect band gap of approximately 1.12 electron volts at room temperature, which means that transitions between the valence band maximum and the conduction band minimum require both a change in energy and a change in crystal momentum. This indirect gap makes silicon a poor light emitter but an excellent material for logic devices, where optical emission is not required. Silicon's abundance in the Earth's crust, its stable native oxide (silicon dioxide), which serves as an excellent gate dielectric and isolation material, and the maturity of its processing technology explain its dominance. The NIST compilation of energy band gaps in elemental and binary semiconductors provides authoritative reference values for silicon and related materials across temperature ranges.

Germanium

Germanium was the semiconductor used in the first practical transistors, demonstrated at Bell Laboratories in 1947, before silicon processing technology caught up and displaced it through the 1960s. Like silicon, germanium has a diamond cubic crystal structure and an indirect band gap, but its gap is narrower, approximately 0.67 electron volts at room temperature. The narrower gap gives germanium higher intrinsic carrier concentration and higher electron and hole mobilities than silicon, making it attractive for high-speed transistors and infrared detectors that must operate at photon energies below silicon's detection threshold. Germanium has seen renewed interest in advanced CMOS technology, where germanium-channel p-type MOSFETs offer hole mobilities several times higher than silicon. The electronic band structure of silicon and germanium has been studied extensively as the baseline for understanding compound semiconductor alloys.

Doping and Carrier Control

The electrical behavior of elemental semiconductors is controlled through doping: introducing substitutional impurity atoms from adjacent groups of the periodic table. In silicon, phosphorus and arsenic (Group V elements) donate an extra electron per atom, creating n-type material with free electrons as majority carriers. Boron (Group III) accepts an electron from the lattice, leaving a mobile hole and creating p-type material. Carrier concentrations can be varied over many orders of magnitude through ion implantation, diffusion, or epitaxial growth, enabling the precise control required for transistor and diode fabrication. The fundamental relationship between doping, carrier concentration, and the Fermi level is described by Fermi-Dirac statistics, and this understanding is documented in depth in arxiv studies addressing silicon's indirect band gap origin.

Applications

Elemental semiconductors have applications in a wide range of fields, including:

• CMOS logic and memory devices that form the core of microprocessors and storage chips
• Photovoltaic solar cells, predominantly silicon-based, for electricity generation
• Power electronics in silicon-based MOSFETs and IGBTs for motor drives and inverters
• Infrared photodetectors using germanium for fiber-optic communication and thermal imaging
• Radiation detectors employing high-purity germanium for gamma-ray spectroscopy