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High Brightness Light Emitting Diodes

High Brightness Light Emitting Diodes. Chapter 1 Chapter 2 屠嫚琳. Materials issues in high-brightness light-emitting diodes. Techniques for production of III-V semiconductors for LEDs Specific materials systems. Techniques for production of III-V semiconductors for LEDs.

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High Brightness Light Emitting Diodes

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  1. High Brightness Light Emitting Diodes Chapter 1 Chapter 2 屠嫚琳

  2. Materials issues in high-brightness light-emitting diodes • Techniques for production of III-V semiconductors for LEDs • Specific materials systems 屠嫚琳

  3. Techniques for production of III-V semiconductors for LEDs • Liquid-Phase Epitaxy (LPE) • Vapor-Phase Epitaxial (VPE) • Molecular Beam Epitaxy (MBE) • Organometallic Vapor-Phase Epitaxy (OMVPE) 屠嫚琳

  4. Liquid-Phase Epitaxy (LPE) • LPE is the simplest technique mechanically. • It is an excellent technique for the production of the very thick layers used in some high-brightness LED structures. 屠嫚琳

  5. Molecular Beam Epitaxy (MBE) • MBE is the most powerful technique for the production of superlattice and quantum-well structures. • MBE can be used for the growth of a wide range of materials, but a notable shortcoming is the difficulty experienced with the growth of the phosphides. 屠嫚琳

  6. Organometallic Vapor-Phase Epitaxy (OMVPE) • OMVPE is the most versatile technique for the production of III-V materials and structures for eletronic and photonic device. • It is also the most recent technique to be devoloped for the production of high-quality III-V semiconductors. 屠嫚琳

  7. Driving force of growth technique 屠嫚琳

  8. Specific materials systems • AlGaAs • AlGaInP • AlGaInN 屠嫚琳

  9. AlGaAs • AlGaAs was the first material for which very high brightness LEDs were demonstrated. • The AlGaAs system is nearly lattice-matched to the GaAs substrates for all compositions. • When the Al content increases, the bandgap becomes large and indirect.With increasing Al composition, the wavelength will also decrease. 屠嫚琳

  10. AlGaInP • The AlGaInP system was identified early as one of the most promising for high-performance LEDs. • AlGaInP have high external quantum efficiency, like 20% at 630 nm, 10% at 590 nm, and 2% at 570 nm. 屠嫚琳

  11. AlGaInN • AlGaInN are very differently from the conventional III-V semiconductors.Due to they have large bond strengths, so they require high growth tempertures. • They can be grown on SiC and sapphire, but the lattice match between GaN and SiC is much better than for sapphire. 屠嫚琳

  12. Overview of device issues in high-brightness light-emitting diodes • Introduction • Internal Quantum Efficiency • Light Extraction 屠嫚琳

  13. Introduction • 1962 : GaAsP LED (Red) • 1970 : GaP:N LED (Green) GaAsP:N (Red~Yellow) • 1980s : AlGaAs LED (Red) • 1990s : AlInGaP LED (Red~Green) • 1993 : GaInN LED (entirevisiblespectralregion) 屠嫚琳

  14. Evolution of LED Performance 屠嫚琳

  15. Luminous performance of high performance LED 屠嫚琳

  16. Internal Quantum Efficiency • High purity and low defect density substrates and epitaxial structures • A direct semiconductor energy gap covering the desired color region • A lattice-matched materials system enabling the growth of heterostructure devices with low defect densities 屠嫚琳

  17. Light extraction • The extraction efficiency is the fraction of generated light that escapes from the semiconductor chip into the surrounding air. 屠嫚琳

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