Arsenic

Arsenic (As, atomic number 33) is a brittle, steel-grey metalloid in Group 15 of the periodic table, isoelectronic with phosphorus and antimony, and one of the oldest known toxic substances in human history. With a density of 5.727 g/cm³ and a unique sublimation behavior — grey arsenic sublimes at 887 °C at standard pressure without passing through a liquid phase — it occupies an unusual position among the semi-metals. Its most stable and commercially relevant allotrope, grey (metallic) arsenic, adopts a layered rhombohedral crystal structure (A7 type) isostructural with antimony and bismuth, with strong covalent bonding within bilayers and weak van der Waals forces between them. This anisotropic structure governs its directional electrical conductivity (~34 nΩ·m along the c-axis), thermal properties (50.7 W/m·K), and mechanical brittleness (Mohs 3.5, no measurable ductility at room temperature).

Arsenic's defining role in modern technology is as the Group V constituent of gallium arsenide (GaAs) and related III-V compound semiconductors. GaAs has an electron mobility of 8,500 cm²/V·s — approximately six times that of silicon — and a direct bandgap of 1.42 eV, making it ideal for high-frequency transistors, laser diodes, solar cells, and LEDs. InAs (Eg = 0.36 eV, electron mobility ~33,000 cm²/V·s) is used in mid-infrared photodetectors and high-electron-mobility transistors (HEMTs). AlGaAs, InGaAs, and AlGaAsP alloys form the heterostructure layers in virtually all compound semiconductor laser and photovoltaic devices. Arsenic is also a well-established n-type dopant in silicon and germanium microelectronics, with a diffusion coefficient that gives it excellent shallow-junction control in CMOS fabrication.

In its +3 and +5 oxidation states, arsenic forms a broad range of compounds with varied industrial relevance. Arsenic trioxide (As₂O₃) — historically used as a poison and pesticide — has found modern application as a chemotherapy agent (Trisenox) for acute promyelocytic leukaemia. Arsenic pentoxide (As₂O₅) is used in glass manufacturing to improve UV transparency and bubble removal. Chromated copper arsenate (CCA) was a major wood preservative until phase-out in many jurisdictions due to environmental concerns. The compound arsine (AsH₃) is a critical MOCVD and MOVPE precursor gas for compound semiconductor epitaxy, though its extreme toxicity (IDLH 3 ppm) demands rigorous engineering controls.

Goodfellow provides high-purity arsenic (As) tailored to meet the needs of specialized industries and research fields. One of its most notable uses is in the production of gallium arsenide (GaAs) semiconductors, which are widely employed in high-speed electronic devices such as mobile phones, satellite communications systems, and light-emitting diodes (LEDs). Arsenic compounds also play a role in the manufacturing of specialized glass used in optics and infrared technologies. Furthermore, arsenic is used as a doping agent in silicon-based electronics to enhance conductivity and performance. Beyond electronics, arsenic is being explored for its potential applications in advanced materials research, particularly in areas like quantum computing and optoelectronics. Its ability to form stable compounds opens up possibilities for creating innovative materials with tailored properties. Goodfellow's arsenic products support groundbreaking research into next-generation electronic devices while contributing to advancements in optical technologies.