Ch 1 Introduction Optoelectronic devices devices deal with

Ch. 1 Introduction • Optoelectronic devices: - devices deal with interaction of electronic and optical processes • Solid-state physics: - study of solids, through methods such as quantum mechanics, crystallography, electromagnetism and metallurgy • Elemental semiconductors: - Si, Ge, . . etc. - indirect bandgap, low electric-optics conversion efficiency • Compound semiconductors - III-V (e. g. Ga. N, Ga. As), II-VI - direct bandgap, high electric-optics conversion efficiency • Ga. As, In. P - higher mobility than Si, Ge, - energy band gap, Eg: 1. 43 (Ga. As), 1. 35 (In. P) - most common substrate, used to grow up compound semiconductors

Periodic Table

Band structure • Band structure: - results of crystal potential that originates from equilibrium arrangement of atoms in lattice - directed from potential model and electron wave equation (Schrodinger equation) time-dependent Schrodinger equation E: electron energy, φ: wave equation, m: electron mass, ħ: Plank constant

Electron energy band diagram v. s. wave number

Energy bandgap v. s. lattice constant

Bonding in solids • Van der Waals bonding: formation of dipoles between atoms and their electrons e. g. : inert gas, like Ar • Ionic bonding: electron exchange between atoms produces positive and negative ions which attract each other by Coulomb-type interactions e. g. Na. Cl, KCl • covalent bonding sharing of electrons between neighboring atoms e. g. : elemental and compound semiconductors • Metallic bonding: valence electrons are shared by many atoms (bonding not directional, electron free or nearly free contributed to conductivity) e. g. : Zn

Body-Centered Cubic (BCC) structure • http: //stokes. byu. edu/bcc. htm e. g. iron, chromium, tungsten, niobium

Face-Centered Cubic (FCC) structure e. g. : aluminum, copper, gold, silver • http: //stokes. byu. edu/fcc. htm

Diamond Cubic (FCC) structure • http: //zh. wikipedia. org/zh-tw/File: Diamond_Cubic-F_lattice_animation. gif

Zincblende structure • Diamond structure, e. g. : Si, Ge Zincblende structure e. g. : aluminum, Ga. As

Atomic arrangement in different solids

Dislocation & strain • Dislocation occurs if - epitaxial layer thickness > hc (critical thickness), or - epitaxial layer thickness < hc, but with large mismatch • Strain occurs if - epitaxial layer thickness < hc, and with small mismatch

Strain semiconductor • a) lattice match b) compressive strain c) tensile strain • Strain offer flexibility for restriction of lattice mismatch

Crystal Growth • Bulk growth: - furnace growth - pulling technique • Epitaxial growth: - Liquid Phase Epitaxy (LPE) - Vapor Phase Epitaxy (VPE), or termed Chemical Vapor Deposition (CVD) - Molecular Beam Epitaxy (MBE)

Epitaxy • epi means “above” taxis means “in order manner” epitaxy can be translated to “to arrange upon” • with controlled thickness and doping • subtract acts as a seed crystal, deposited film takes on a lattice structure and orientation identical to the subtract • different from thin film deposition that deposit polycrystalline or amorphous film • - homoepitaxy: epi and subtract are with the same material epi layer more pure than subtract and have different doping level - hetroepitaxy: • used for - Si-based process for BJT and CMOS, or - compound semiconductors, such as Ga. As

Epitaxy Material Growth Methods • Liquid Phase Epitaxy • Vapor Phase Epitaxy (VPE), or termed Chemical Vapor Deposition (CVD) - formation of condensed phase from gas of different chemical composition - distinct from physical vapor deposition (PVD) such as sputtering, e-beam deposition, MBE (condensation occurs without chemical change) - gas stream through a reactor and interact on a heated subtract to grow epi layer • Molecular Beam Epitaxy

Doping of Semiconductors • Intrinsic materials: undoped - Undoped materials by epitaxy technology have more carriers than in intrinsic material. e. g. Ga. As: 1013 /cm 3 (instrinsic carrier concentration: 1. 8 x 106 /cm 3) - impurity comes from source materials, carrier gases, process equipment, or subtract handle • Extrinsic materials: - n-type: III sub-lattice of III-V compound is substituted by V elements: impurity terms “donor” - p-type: V sub-lattice of III-V compound is substituted by III elements: impurity terms “acceptor” http: //www. siliconfareast. com/sigegaas. htm

Optical fiber - lowest loss at 1. 55 um - lowest dispersion” 1. 3 um

Energy band theory