Abstract

Indium arsenide (InAs) is a III-V semiconductor compound with the chemical formula InAs and molar mass of 189.740 grams per mole. The material crystallizes in the zinc blende structure with a lattice constant of 6.0583 Å and exhibits a direct bandgap of 0.354 electronvolts at 300 Kelvin. Characterized by exceptionally high electron mobility reaching 40,000 square centimeters per volt-second, InAs demonstrates significant applications in infrared optoelectronics and high-frequency electronic devices. The compound melts at 942 degrees Celsius with a density of 5.67 grams per cubic centimeter. Thermodynamic parameters include a standard enthalpy of formation of -58.6 kilojoules per mole and standard Gibbs free energy of formation of -53.6 kilojoules per mole. The entropy measures 75.7 joules per mole-kelvin with a heat capacity of 47.8 joules per mole-kelvin.

Introduction

Indium arsenide represents a fundamental III-V semiconductor compound within the broader class of binary arsenides. Classified as an inorganic crystalline solid, this material occupies a critical position in semiconductor physics and materials science due to its unique electronic properties. The compound manifests as grey cubic crystals with metallic luster and demonstrates semiconductor behavior despite its metallic appearance. Industrial significance stems primarily from its narrow direct bandgap and exceptional charge carrier mobility, properties that enable advanced optoelectronic applications across the infrared spectrum. The material's discovery and development paralleled the broader advancement of III-V semiconductor technology during the mid-20th century, with systematic investigation of its properties beginning in the 1950s as part of semiconductor materials research programs.

Molecular Structure and Bonding

Molecular Geometry and Electronic Structure

Indium arsenide crystallizes in the zinc blende structure (space group F̄3m), characterized by a face-centered cubic lattice with alternating indium and arsenic atoms. Each indium atom coordinates tetrahedrally with four arsenic atoms, and conversely, each arsenic atom coordinates with four indium atoms. The lattice constant measures 6.0583 Å at room temperature, resulting in an In-As bond length of approximately 2.62 Å. This structure derives from the diamond cubic lattice but with two different atom types occupying alternating lattice positions.

The electronic configuration involves indium ([Kr]4d¹⁰5s²5p¹) and arsenic ([Ar]3d¹⁰4s²4p³) atoms forming primarily covalent bonds with partial ionic character due to the electronegativity difference of 0.35 between indium (1.78) and arsenic (2.13) on the Pauling scale. The bonding exhibits sp³ hybridization with bond angles of 109.5 degrees, consistent with tetrahedral coordination. The compound demonstrates direct bandgap behavior with both valence band maximum and conduction band minimum occurring at the gamma point in the Brillouin zone.

Chemical Bonding and Intermolecular Forces

The chemical bonding in indium arsenide predominantly involves covalent interactions with approximately 25% ionic character according to Phillips ionicity scale calculations. The cohesive energy measures approximately 5.8 electronvolts per bond, with bond strength intermediate between purely covalent Group IV semiconductors and more ionic II-VI compounds. In the solid state, primary intermolecular forces include van der Waals interactions between crystal planes and dipole-dipole interactions arising from the charge transfer between indium and arsenic atoms.

The compound exhibits a static dielectric constant of 14.55 and high-frequency dielectric constant of 11.8, reflecting substantial polarizability. The longitudinal optical phonon energy measures 30.2 millielectronvolts, while transverse optical phonon energy reaches 27.1 millielectronvolts. These parameters indicate strong electron-phonon coupling, which influences charge transport properties and thermal characteristics. The bonding energy per atom calculates to approximately 2.9 electronvolts, consistent with the moderate melting point observed experimentally.

Physical Properties

Phase Behavior and Thermodynamic Properties

Indium arsenide melts congruently at 942 degrees Celsius without decomposition, forming a liquid phase with complete miscibility of its components. The solid-phase exists exclusively in the zinc blende structure up to the melting point, with no observed polymorphic transitions. The density measures 5.67 grams per cubic centimeter at 298 Kelvin, decreasing linearly with temperature according to the thermal expansion coefficient of 4.52 × 10^-6 per Kelvin.

The standard enthalpy of formation measures -58.6 kilojoules per mole with a standard Gibbs free energy of formation of -53.6 kilojoules per mole. The entropy content is 75.7 joules per mole-kelvin, while the heat capacity measures 47.8 joules per mole-kelvin at room temperature. The Debye temperature calculates to 280 Kelvin, indicating moderately strong bonding characteristics. The linear thermal expansion coefficient follows the relationship α = 4.52 × 10^-6 + 3.10 × 10^-9T K^-1 over the temperature range 100-800 Kelvin.

Spectroscopic Characteristics

Infrared spectroscopy reveals characteristic phonon absorption bands with Reststrahlen band between 26.5 and 30.5 micrometers corresponding to optical phonon vibrations. Raman spectroscopy shows distinct peaks at 218.8 centimeters^-1 for transverse optical modes and 240.2 centimeters^-1 for longitudinal optical modes. Photoluminescence spectroscopy demonstrates near-bandedge emission at 0.354 electronvolts with linewidth varying from 2 to 10 millielectronvolts depending on crystal quality and temperature.

UV-Vis spectroscopy indicates strong absorption beginning at the band edge with an absorption coefficient exceeding 10⁴ centimeters^-1 for photons above the bandgap energy. The refractive index measures 3.51 at 2 micrometers wavelength, decreasing to 3.42 at 10 micrometers due to dispersion effects. The extinction coefficient remains below 0.1 throughout the transparent region from 3.5 to 8.0 micrometers, making the material suitable for infrared optical applications.

Chemical Properties and Reactivity

Reaction Mechanisms and Kinetics

Indium arsenide demonstrates relative chemical stability in dry air at room temperature but oxidizes slowly upon prolonged exposure to atmospheric conditions. The oxidation process follows parabolic kinetics with an activation energy of 95 kilojoules per mole, forming indium oxide and arsenic oxide surface layers. The compound decomposes in strong oxidizing acids such as nitric acid and aqua regia, producing indium and arsenic species in their highest oxidation states.

Reaction with halogens proceeds readily at elevated temperatures, forming indium trihalides and arsenic trihalides. Chlorination occurs at 200 degrees Celsius with complete conversion to InCl₃ and AsCl₃. The material exhibits resistance to alkaline solutions up to pH 12, but dissolves slowly in concentrated potassium hydroxide solutions above 80 degrees Celsius. Thermal decomposition begins above 600 degrees Celsius under vacuum conditions, with arsenic sublimation leading to indium-rich surfaces.

Acid-Base and Redox Properties

Indium arsenide behaves as a Lewis acid through indium centers and as a Lewis base through arsenic atoms, though these properties manifest primarily in surface reactions rather than bulk behavior. The compound demonstrates amphoteric character in extreme conditions, dissolving in both strong acids and strong bases through oxidation processes. Standard reduction potential for the InAs/In + As system calculates to approximately -0.34 volts relative to the standard hydrogen electrode.

The material exhibits remarkable stability in non-oxidizing environments up to 600 degrees Celsius. Redox reactions typically involve oxidation of both constituent elements, with indium converting to +3 oxidation state and arsenic to +3 or +5 oxidation states depending on oxidant strength. The compound does not demonstrate significant proton exchange behavior in aqueous systems due to its limited solubility and covalent network structure.

Synthesis and Preparation Methods

Laboratory Synthesis Routes

Laboratory synthesis of indium arsenide typically employs direct combination of stoichiometric amounts of high-purity indium and arsenic elements. The process occurs in sealed quartz ampoules under vacuum conditions to prevent oxidation and component loss. The reaction proceeds according to the equation: In + As → InAs, with careful temperature programming to control reaction kinetics and prevent explosive arsenic vaporization.

Standard synthesis protocols involve heating the elements to 300 degrees Celsius for arsenic sublimation and homogenization, followed by gradual heating to 950 degrees Celsius over 24 hours. The melt maintains at this temperature for 12 hours to ensure complete reaction, followed by controlled cooling at 10 degrees Celsius per hour through the solidification point. This process yields polycrystalline ingots with typical purity levels exceeding 99.999% for electronic applications. Zone refining techniques further purify the material by progressive melting and recrystallization.

Industrial Production Methods

Industrial production utilizes modified Bridgman-Stockbarger techniques or liquid encapsulated Czochralski pulling for single crystal growth. The Bridgman method employs vertical translation of sealed ampoules through temperature gradients exceeding 50 degrees Celsius per centimeter, producing crystals up to 10 centimeters in diameter. Czochralski growth requires boric oxide encapsulation to suppress arsenic volatility at the melting point, with pulling rates of 5-15 millimeters per hour under controlled atmosphere conditions.

Production scale processes yield approximately 5000 kilograms annually worldwide, with primary manufacturing facilities in the United States, Japan, and Germany. Material costs range from $100 to $500 per gram depending on purity and crystalline perfection requirements. Environmental considerations include arsenic containment systems and waste treatment facilities to manage toxic byproducts. Modern production facilities achieve arsenic recovery rates exceeding 99.8% through closed-loop systems and scrubber technologies.

Analytical Methods and Characterization

Identification and Quantification

X-ray diffraction provides definitive identification through comparison with standard pattern JCPDS 15-0869 for zinc blende InAs. Characteristic diffraction peaks occur at 2θ = 25.3° (111), 29.6° (200), 41.9° (220), and 49.5° (311) using Cu Kα radiation. Energy-dispersive X-ray spectroscopy confirms stoichiometry with characteristic indium Lα (3.29 kiloelectronvolts) and arsenic Kα (10.5 kiloelectronvolts) emission lines.

Quantitative analysis employs inductively coupled plasma mass spectrometry with detection limits of 0.1 parts per million for metallic impurities. Hall effect measurements determine electrical parameters including carrier concentration (10¹⁵-10¹⁷ centimeters^-3) and mobility (20,000-40,000 square centimeters per volt-second) with accuracy within 5%. Secondary ion mass spectrometry profiles impurity distributions with depth resolution better than 5 nanometers and detection sensitivity below 10¹⁵ atoms per cubic centimeter.

Purity Assessment and Quality Control

Electronic grade material specifications require total metallic impurities below 1 part per million and carbon/oxygen concentrations under 0.1 parts per million. Residual donor concentrations typically measure 1-5 × 10¹⁵ centimeters^-3 with compensation ratios below 0.3. X-ray rocking curve full width at half maximum values below 30 arcseconds indicate high crystalline perfection for epitaxial substrates.

Industrial quality standards include dislocation densities below 1000 per square centimeter and etch pit densities under 500 per square centimeter. Surface roughness specifications require root mean square values below 0.3 nanometers over 10 × 10 micrometer areas for epitaxial readiness. Storage conditions mandate dry nitrogen atmosphere to prevent surface oxidation, with shelf life exceeding five years under proper containment.

Applications and Uses

Industrial and Commercial Applications

Infrared photodetectors constitute the primary application, with cutoff wavelengths near 3.8 micrometers at room temperature. Photovoltaic detectors achieve detectivity values exceeding 10¹¹ centimeters·√hertz/watt at 3.0 micrometers when operated at 195 Kelvin. Laser diodes fabricated from InAs/InAsSb superlattices emit in the 3-5 micrometer atmospheric window with output powers reaching 100 milliwatts in continuous wave operation.

High-electron-mobility transistors utilize InAs channels grown on gallium arsenide or indium phosphide substrates, achieving cutoff frequencies beyond 500 gigahertz. These devices demonstrate transconductance values exceeding 1.5 siemens per millimeter at room temperature. Magnetic field sensors based on the giant magnetoresistance effect in InAs quantum wells detect fields below 10 microtesla with linear response up to 5 tesla.

Research Applications and Emerging Uses

Topological insulator research employs InAs/GaSb type-II superlattices exhibiting quantum spin Hall effects at temperatures up to 10 Kelvin. These systems demonstrate edge state conduction with quantized resistance of h/2e² (12.9 kilohms) under magnetic fields below 1 tesla. Quantum computing applications utilize InAs nanowires as Majorana fermion hosts, with signature zero-bias conductance peaks observed below 100 millikelvin.

Terahertz generation via photo-Dember effect produces radiation up to 5 terahertz with conversion efficiencies near 0.1% using femtosecond laser excitation. Quantum dot infrared photodetectors based on self-assembled InAs dots on gallium arsenide achieve multicolor detection from 5 to 20 micrometers with dark currents below 10^-5 amperes per square centimeter at 77 Kelvin. Emerging applications include spin-filter devices and non-reciprocal optical elements exploiting the strong spin-orbit coupling in InAs heterostructures.

Historical Development and Discovery

Initial investigations of indium arsenide began during the 1950s as part of comprehensive studies of III-V semiconductor systems. Early synthesis methods developed at Philips Research Laboratories in the Netherlands produced the first single crystals in 1952 using horizontal zone melting techniques. Band structure calculations by Herman in 1954 correctly predicted the direct bandgap nature and small energy separation between conduction and valence bands.

The first experimental confirmation of high electron mobility occurred in 1956 through Hall effect measurements by Welker at Siemens Research Laboratories, revealing values exceeding 20,000 square centimeters per volt-second at room temperature. Crystal growth improvements during the 1960s enabled production of materials with carrier concentrations below 10¹⁶ centimeters^-3, facilitating detailed investigations of electronic properties. The 1970s saw development of liquid phase epitaxy methods for heterostructure fabrication, while molecular beam epitaxy capabilities emerged during the 1980s enabling quantum well and superlattice structures.

Conclusion

Indium arsenide represents a technologically significant III-V semiconductor characterized by exceptional electron mobility and narrow direct bandgap. The zinc blende crystal structure provides the foundation for its electronic properties, while covalent-ionic bonding contributes to thermal and chemical stability. Applications span infrared optoelectronics, high-frequency electronics, and quantum devices, with ongoing research exploring topological phenomena and quantum information processing. Future developments will likely focus on heterostructure engineering, interface control, and integration with other material systems to exploit the unique properties of this remarkable semiconductor compound.