2B- Optical Technologies

E-Photon One Curriculum 2B- Optical Technologies Coordinator: António Teixeira, Co-Coordinator: K. Heggarty António Teixeira, Paulo André, Rogério Nogueira, Tiago Silveira, Ana Ferreira, Mário Lima, Ferreira da Rocha, João Andrade

Basic Photonic Measurements Material growth and processing Semiconductor materials Transmission systems performance assessment tools Optical Amplifiers Semiconductor Optical Amplifiers (SOAs) Erbium Doped Fiber Amplifiers (EDFAs) Fiber Amplifiers- Raman Other Amplifiers Emitters Semiconductor Fiber 7.Receivers PIN APD Modulators Mach Zehnder Electro-absorption Acoust-optic Filters Fiber Bragg gratings Fabry Perot Mach-Zehnder Isolators Couplers Switches Mechanical Wavelength converters Multiplexers/ Demultiplexers Program E1- 2b Optical technologies

Paulo André Material Growth and Processing

2. Material Growth and Processing 1.1. States of Matter (2) 1.2. Material Structure (16) 1.3. Brillouin zones (2) 1.4. Miller indexes (2) 1.5. Growing Steps and Processes (13) 1.6. Manufacture of Microelectronic devices (1) 1. Photolithography (10) 2. p-n junction manufacture (4) E1- 2b Optical technologies

States of Matter • Gaseous • Liquid • Solid • Crystalline: the long range crystalline order extends to the all of the material. • Polycrystalline:the long range crystalline order is about the same size of the crystals • Amorphous: short range order E1- 2b Optical technologies

States of matter • The macroscopic properties (electrical, optical and mechanical, …)of a material depend on the internal organization of the atoms and also from the interatomic forces that bind them. • Most electronic and optoelectronic devices are made of crystallinematerials where the long range order between atoms is dominant. Diamond Graphyte E1- 2b Optical technologies http://www.iit.edu/~felfkri/report.htm

SiO2 Structure Crystalline Lattice Non-Crystalline Lattice E1- 2b Optical technologies

In a crystalline lattice equivalent points (R and R`) are connected by a lattice vector Structure Primitive Cell – cell defined by primitivevectors (vectors defined by the lesser integer numbers) serves the purpose of being an elementary building block to build the lattice. It can only contain 1 lattice point. E1- 2b Optical technologies

Wigner-Seitz primitive Cell - It’s built not from primitive vectors but from each lattice point, complying to the translation symmetry that binds each point to it’s neighbor. Building: - Connect a lattice point to all its adjacent neighbors; - Draw lines (or a plane) that bisect the previous drawn lines; - An area or volumes that is delimited by these planes is said to be a Wigner-Seitz cell. Structure - Wigner-Seitz Cell http://www.chembio.uoguelph.ca/educmat/chm729/wscells/construction.htm E1- 2b Optical technologies

Structure – Bravais Lattice August Bravais showed that there are only 14 ways to group 3-dimensional points: 14 Bravais lattices. These lattices can be grouped on 7 crystallographic systems. E1- 2b Optical technologies http://folk.uio.no/dragos/Solid/FYS230-Exercises.html

Structure O coordination number (CN) is the number of adjacent neighbors near a given atom. The spatial arrangement depends on: - the ions' relative size - the electrical charge balance Normally there is a tendency to have bigger packaging in order to minimize the energy The bigger the number of cations that surrounds the central cation, the bigger the stability. A: CN = 4 B: CN= 6 C: CN= 8 D, E: CN= 12 E1- 2b Optical technologies

Structure - cubic - simple cubic (sc) 1 atom per unitary cell 8x(1/8 dos vertices)=1 Conventional cell volume : ao3 APF=0.524 Number of adjacent neighbors: 6 Distance to closer neighbors: ao E1- 2b Optical technologies

Structure - cubic - Corpus centered cubic (CCC) 2 atoms per unitary cell 8x(1/8 of the vertices)+1=2 conventional cell volume : ao3 APF=0.68 Number of adjacent neighbors : 8 Distance to closer neighbors : http://tftlcd.kyunghee.ac.kr/lecture/solid_state_physics/chapter1.html http://www.jwave.vt.edu/crcd/farkas/lectures/structure/tsld005.htm E1- 2b Optical technologies

Structure - cubic – Face Centered Cubic (FCC) 4 atoms per unitary cell 8x(1/8 of the vertices)+ 6x(1/2 of the faces)=4 Volume of each conventional cell : ao3 APF=0.74 Number of adjacent neighbors : 12 Distance to closer neighbors : http://www.jwave.vt.edu/crcd/farkas/lectures/structure/tsld002.htm E1- 2b Optical technologies

Structure - compact - hexagonal (CH) 6 atoms per unitary cell APF=0.74 Number of adjacent neighbors : 12 • The spatial lattice is simply hexagonal, with a two atoms base associated to each lattice point E1- 2b Optical technologies

Structure - Crystalline - NaCl (sodium chloride) type • Coordination Number = 6 • Anion with FCC structure • Cation placed centrally in the cube and in the middle of each of its 12 edges => Two interpenetrated FCC lattices • MgO, FeO, MnS, LiF E1- 2b Optical technologies

Structure - Crystalline - CsCl (Cesium Chloride) type • Coordination Number = 8 • Anions on the cube vertices • Cation on the center of the cube • CsBr, CsI E1- 2b Optical technologies

Structure – Crystalline-type CdS (Wurtzite) • Coordination Number = 4 • Anions with a CH arrangement • Cations with a CH arrangement => 2 interpenetrated CH lattices • ZnO, AlN, GaN, ZnS E1- 2b Optical technologies

Structure - Crystalline structures of ZnS (zinc-blende) • Coordination Number = 4 • Anions with a FCC arrangement • Cations occupy tetrahedricpositions • SiC, BeO, CuCl, GaAs E1- 2b Optical technologies

Structure - diamond type • 8 atoms per unitary cell • FCC lattice com um motivo de dois átomos • Coordination Number = 4 => 2 FCC lattices interpenetrated at ¼ of the diagonal of the body structure) • Si, C, Ge E1- 2b Optical technologies

Structure - Reciprocal Lattice Each crystalline structure has two lattices: the crystallinelattice and the reciprocal lattice. The set of all wave vectors that generate plane waves with a periodicity taken from the Bravais lattices, is the reciprocallattice. The vectors that define the reciprocal lattice’s axis are deduced from the primitive vectors of the crystalline network. E1- 2b Optical technologies

Structure The reciprocal lattice vector can be defined by: Ghkl = h b1+k b2+ l b3 with h, k and l integer numbers The crystalline lattice vectors have dimension L The reciprocal lattice vectors have dimension L-1 E1- 2b Optical technologies

1st Brillouin zone As in the case of a direct lattice, where a primitive cell containing a single lattice point using translational symmetry can build the entire sapce without superposition and still mantain full lattice symmetry – Wigner-Seitz cell Also in the reciprocalspace, and by analogy with the Wigner-Seitz cell, a 1st Brillouin zone can be built If a Wigner-Seitz cell has volume V, the Brillouin zone will have 2/V 1st Brillouin zone for a 1-D lattice E1- 2b Optical technologies

1st Brillouin zone for a simple cubic lattice 1st Brillouin zone for an hexagonal lattice 1st Brillouin zone for a face centered cubic lattice : truncated Octahedral 1st Brillouin zone for a face centered cubic lattice: rhombic dodecahedral http://cst-www.nrl.navy.mil/bind/kpts/ E1- 2b Optical technologies

Miller indexes In order to identify the planes and directions of a crystalline lattice, Miller indexes are used. • - Choose an axis system whose origin isn’t over the plane • - determine the plane intersections with the crystallographic axis • - Invert • - Simplify the fractions to minimum integer possible • - This values are the Miller indexes (h,k,l) of the plane • - The negative direction must be signaled with a line above • Identical plane family. Z Y (001) (002) (111) X (100) E1- 2b Optical technologies

E1- 2b Optical technologies

Growing Steps Initial Material Polycrystalline Material monocrystalline Material Wafers Devices Quimical Processing Growth Techniques Cutting and polishing Semiconductor Layer Deposition E1- 2b Optical technologies

Monocrystal Growing • The purpose of the growing techniques: • - produce ingots with the least amount of imperfections and with the biggest diameter. • For Si, it is possible to grow ingots • with about l=100cm and = 30cm. - For Si, GaAs and InP semiconductors, there are well developed growth technologies. However, for most semiconductors it is difficult to get high quality materials and big dimension substrates. http://www.ent.ohiou.edu/~juwt/HTMLS/semicondmanufactureprocess/crystalgrowing.htm E1- 2b Optical technologies

Semiconductor Growth Czochralski – single crystal Wafers http://www.nikkohitech.com/ E1- 2b Optical technologies

Czochralski Method • A solid material seed is dived in the molten material • The seed is slowly pulled in order to promote the solidification of the grasped molten material • O crystal is slowly turned around its axis in order to get a circular section. http://www.ent.ohiou.edu/~juwt/HTMLS/semicondmanufactureprocess/crystalgrowing.htm E1- 2b Optical technologies

Si monocrystal Growth Typical Growth Environment: Fusion Temperature = 1420ºC Growth Speed = 2mm/min Growth Atmosphere = Argon E1- 2b Optical technologies http://www.sumitomometals.co.jp/e/business/silicon.html

After growing the ingot, several steps have to be taken until actually having a substrate; Remove the seed and the other ingot end; Rectify the surface and define the diameter; Mark the crystallographic orientations, by making one or more plain regions over the ingot length; Cut in a disc shaped way; Polish the discs. http://materiaali.tkk.fi/en/PhysicalMetallurgy/English/high1.html E1- 2b Optical technologies

Real crystals aren’t perfect since they have crystalline periodicity irregularities - flaws. The presence of this flaws affects the electrical, mechanical and optical properties. Point defects: a) substitutional impurities b) interstitial impurities c) hole d) Frenkel and Schottky flaw Crystal Characterization E1- 2b Optical technologies

Epitaxial Growth The wafers grown through the described techniques are rarely used in direct device manufacture, but are used as substrates instead. Solution : grow one or more layers (of some m thickness) over them. The epitaxial growth techniques have low growth rate (as low as one single layer per second in some techniques) which allows an high precision size control in the growth direction, which is essential for the heterostructure variety that is nowadays used in optoelectronic devices. E1- 2b Optical technologies

Molecular Beam Epitaxy (MBE) The MBE technique is one of the more important heterostructure manufacture techniques for optoelectronic devices Almost all semiconductors have been grown through this technique • MBE is a growth technique that involvs the reaction of one or more atom beams with the substract surface http://www.elettra.trieste.it/experiments/beamlines/lilit/htdocs/people/luca/tesihtml/node24.html E1- 2b Optical technologies

When an effusion cell is heated, atoms or charged molecules evaporate in the direction of the heated substrate. E1- 2b Optical technologies

An atom or molecule beam is direccioned to the substrate's crystalline lattice, giving rise to a new deposited material layer. • When heating the surface, each atom has enough time to migrate find a new place in the new crystalline lattice. • The MBE growth rate is about one single layer per second. This low growth rate in association to the shutters placed in front of the effusion ovens allows the change of the crystal composition with a single layer control. http://www.wsi.tu-muenchen.de/E24/resources/facilities.htm E1- 2b Optical technologies

The photolithography technique allows the manufacture of complex and dense circuits, improving this way the performance of the devices since it allows for its dimension reductions to happen. Recurring to the lithography technique, it’s possible to manufacture on the same wafer both active and passive devices. The process consists in transferring a previously created pattern/model to the wafer’s surface, in order to define the several regions of an integrated circuit This process has several steps, so all advances in the overall process depend on the development of each of the individual steps. Photolithography E1- 2b Optical technologies

Spin Coating A little piece of photosensitive material is placed on the center of the wafer. The wafer is then spinned over its axis in order to promote a uniform spacing of the material. Base Material : polyisopropene Conditions: rotation speed: 2000-8000rpm time: 10-60s thickness: 0.7 - 1.0m thermical treatment : 100ºC Photolithographic Process Steps 1 - Deposition of the photosensitive film The photolithography process must be implemented in a clean room, in order to avoid dust to be deposited in the mask and wafer. E1- 2b Optical technologies

The photosensitive film when receiving radiation can behave as: - Positivephotosensitive : The images formed are the same as the ones in the mask. - Negativephotosensitive: The images formed are complementary to the ones in the mask. The radiation exposed regions become insoluble and therefore can not be removed. 2- Photosensitive film to radiation • The transfer of the model from the mask to the wafer can be done using optic equipment (for details bigger than 0.25m), X-rays or by an electron beam. E1- 2b Optical technologies

Positive Photosensitive : It’s built by 3 components: a resin, a photosensitive element and an organic solvent. The region exposed to radiation changes its chemical structure becoming soluble. The broken connections between the molecules allow an easy removal. Negative Photosensitive : Polymers are combined with a photosensitive element. The region exposed to radiation become insoluble due to the cross connections formed between the molecules. The high molecular weight of the molecules prevents their removal. E1- 2b Optical technologies

Exposure Response Curves and their transversal sections Photosensitive film fully soluble for an energy equaling ET Photosensitive film fully insoluble for an energy equaling 2ET E1- 2b Optical technologies

The next step is the Writing/Recording process, That must allow the removal of material in the regions where the photosensitive film doesn’t exist. 3- Writing/Recording Process SiO2 is selectively attacked, whereas the substrate remains unaltered E1- 2b Optical technologies

The simplest recording process is chemical recording: - It involves a chemical reaction followed by the removal of reaction elements. - The elements used for chemical attacks are mostly acids (HF, HNO3, H4C2O2, H2SO4). E.g. : SiO2 + 6HF -> H2SiF6 + 2H2O Water can be used as diluent for this attacker E1- 2b Optical technologies

The Attack depends on the orientation degree: Some solutions are more easily solved in some specific crystallographic planes. The material used in the attack should attack only one layer at a time and should be self-limitative. Chemical recording is simple and cheap, however it’s neither compatible with submicrometric technologies nor permits an anisotropic attack. E1- 2b Optical technologies

After the recording, the photosensitive film must be removed 4 – Film Removal Usually, the film removal is made by chemical attack E1- 2b Optical technologies

Manufacture Steps of a p-n junction Oxidation - Forming a SiO2 layer. - Works as an insulator or barrier to diffusion or implantation Litographic Process - The wafer is covered by a photosensitive film; - Radiation Exposure through a mask; - The non-polymerized regions are solved; - Thermical Treatment (120-180ºC) to boost the film adhering; - Attack with HF to remove the uncovered SiO2; - Photosensitive film removal through a chemical solution or through an attack of oxygen plasma. E1- 2b Optical technologies

In order to form active elements in integrated circuits it’s necessary to selectively introduce dopants in the substrate; The surface is exposed to an high ion dopant concentration, that are incorporated in the semiconductor crystal lattice; The SiO2 layeris a barrier to diffusion and to the impurity implantation. E1- 2b Optical technologies

2B- Optical Technologies