Materiale electrotehnice noi

Materiale electrotehnice noi Materiale semiconductoare noi Facultatea de Inginerie Electrica, Materiale electrotehnice noi, 2009-2010, master IPE, anul I Prof.dr.ing.Florin Ciuprina

Structura disciplinei

Materiale semiconductoare • Materiale semiconductoare clasice • Polimeri semiconductori • Materiale semiconductoare nanostructurate • Aplicatii moderne

Materiale semiconductoare clasice Siliciu (Si) • cristalizeaza in retea de tip diamant • utilizari: • circuite integrate • diode • tiristoare • tranzistoare • baterii solare • traductoare Hall

Materiale semiconductoare clasice Germaniu (Ge) • cristalizeaza in retea de tip diamant • utilizari: • diode tunel • tranzistoare • detectoare de radiatii • traductoare Hall • termometre pentru temperaturi joase

Materiale semiconductoare clasice Seleniu (Si) • prezinta o mare varietate de stari alotropice: sticlos, amorf, cristalin • utilizari: fotoelemente, redresoare etc. Carbura de siliciu (SiC) • prezinta o mare varietate de politipuri cristaline • utilizari: varistoare si dispozitive de mare putere, rezistente la radiatii, care lucreaza la frecvente si temperaturi mari

Materiale semiconductoare clasice Compusi semiconductori AII - BVI • ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe • utilizari: fotorezistoare, generatoare Hall, traductoare de presiune etc. Compusi semiconductori AIII - BV • InSb, InAs, InP, GaSb, GaAs, AlSb • utilizari: diode tunel, tranzistoare, in optoelectronica etc.

Polimeri conductori Polimerii dupa anii ’70: • ieftini, • rezistenta mecanica foarte buna, • flexibili • izolatori electrici (σ < 10-7 S/m) • prin dopare unii polimeri pot deveni conductori sau semiconductori.

Polimeri semiconductori Conditii de obtinere: • Polimer realizat prin alternarea de legaturi simple si legaturi duble (conjugate) = polimer conjugat • Perturbarea polimerului conjugat prin dopare: • extragere de electroni (oxidare) • dopanti acceptori (tip p): I2, PF6, BF6, Cl, AsF6 • introducere de electroni (reducere) • dopanti donori (tip n): Na, K, Li, Ca

Polimeri semiconductori Structuri uzuale: Polyethylenedioxythiophene (PEDOT) Polyphenylene vinylene (PPV) Polydialkylfluorene

Polimeri semiconductori Conductia electrica: • deplasarea intramoleculara a cvasi-particulelor (solitoni, polaroni, bipolaroni) create prin dopare • transferul intermolecular al sarcinilor electrice prin “intersoliton hopping”

Polimeri semiconductori Conductia electrica: • deplasarea intramoleculara a cvasi-particulelor (solitoni, polaroni, bipolaroni) create prin dopare

Polimeri semiconductori Conductia electrica: • deplasarea intramoleculara a cvasi-particulelor (solitoni, polaroni, bipolaroni) create prin dopare Formarea si deplasarea unui polaron in poliacetilena

Polimeri semiconductori Conductia electrica: • deplasarea intramoleculara a cvasi-particulelor (solitoni, polaroni, bipolaroni) create prin dopare

Polimeri semiconductori Conductia electrica: • deplasarea intramoleculara a cvasi-particulelor (solitoni, polaroni, bipolaroni) create prin dopare • transferul intermolecular al sarcinilor electrice prin “intersoliton hopping” Intersoliton hopping: solitoni incarcati su sarcina (jos) sunt fixati de catre ionii dopantului, in timp ce solitonii neutri (sus) se misca liber. Un soliton neutru de pe un lant apropiat de un lant cu un soliton incarcat cu sarcina pot interactiona si electronul solitonului neutru sare dintr-un defect in altul.

Polimeri semiconductori Controlul dopajului:

Aplicatii ale polimerilor semiconductori Tranzistoare cu efect de camp – FET poli(o-metoxianilina) - POMA

Aplicatii ale polimerilor semiconductori Polimer LED - PLED

Materiale semiconductoare nanostructurate • Filme din siliciu policristalin (poly-Si) • metoda de fabricatie: depunere chimica de vapori la presiune scazuta si temperaturi de peste 600 °C, utilizand silan ca gas precursor. • avantaje fata de Si monocristalin: mobilitatea purtatorilor este cu cateva ordine de marime mai mare, are stabilitate mai mare sub actiunea solicitarilor campului electric si a luminii. • utilizari: celule solare pentru panouri solare de, circuite integrate la scara mare, MEMS, tranzistoare TFT etc.

Materiale semiconductoare nanostructurate • Filme nanostructurate din oxizi metalici (TiO2, SnO2, ZnO) • metoda de obtinere: prin hidroliza controlata din suspensii coloidale preformate • utilizari: senzori de gaz, celule fotovoltaice

Materiale semiconductoare nanostructurate • Filme din oxizi metalici modificate cu produsi semiconductori AII – BVI (CdSe, CdS, CdTe) • metoda de obtinere: prin precipitare chimica a produsilor AII – BVI direct pe substrat, si absorbtia selectiva a ionilor din solutie. • utilizari: LED-uri, microelectronica

Aplicatii moderne ale semiconductorilor Ecrane cu cristale lichide (LCD) • Cristale lichide (faze mezomorfe, mezofaze): materiale care pot sa curga ca un lichid, dar ale caror molecule pot fi orientate ca intr-un cristal; • Materiale: compusi organici (cianobifenil), compounduri polimerice etc. • Mezofaze: nematice, smectice, chiralice, albastre. cianobifenil

Aplicatii moderne ale semiconductorilor Ecrane cu cristale lichide (LCD) • folosesc cristale lichide cu structuri nematic rasucite TN (twisted nematic)

Aplicatii moderne ale semiconductorilor Ecrane cu cristale lichide (LCD) cu matrice activa (tehnologie TFT) cu matrice pasiva

Aplicatii moderne ale semiconductorilor Laseri (Light Amplification by Stimulated Emission of Radiation) Caracteristici: • lumina monocromatica • lumina unidirectionala • lumina coerenta (“organizata”)

Aplicatii moderne ale semiconductorilor Laseri (Light Amplification by Stimulated Emission of Radiation) Tipuri: • Solid-state lasers have lasing material distributed in a solid matrix (such as the ruby or neodymium:yttrium-aluminum garnet "Yag" lasers). The neodymium-Yag laser emits infrared light at 1,064 nanometers (nm). A nanometer is 1x10-9 meters. • Gas lasers (helium and helium-neon, HeNe, are the most common gas lasers) have a primary output of visible red light. CO2 lasers emit energy in the far-infrared, and are used for cutting hard materials. • Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet range. • Dye lasers use complex organic dyes, such as rhodamine 6G, in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths. • Semiconductor lasers, sometimes called diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, such as the writing source in some laser printers or CD players.

Aplicatii moderne ale semiconductorilor Laseri (Light Amplification by Stimulated Emission of Radiation)

Aplicatii moderne ale semiconductorilor Laseri (Light Amplification by Stimulated Emission of Radiation) Tipuri: • Medicine: Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry • Industry: Cutting, welding, material heat treatment, marking parts • Defense: Marking targets, guiding munitions, missile defence, electro-optical countermeasures (EOCM), alternative to radar, blinding enemy troops. • Research: Spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry, LIDAR, laser capture microdissection • Product development/commercial: laser printers, CDs, barcode scanners, thermometers, laser pointers, holograms, bubblegrams. • Laser lighting displays: Laser light shows • Laser skin procedures such as acne treatment, cellulite reduction, and hair removal.

Materiale electrotehnice noi