|Published (Last):||15 January 2016|
|PDF File Size:||19.32 Mb|
|ePub File Size:||6.86 Mb|
|Price:||Free* [*Free Regsitration Required]|
You can change your ad preferences anytime. Chapter 4b. Upcoming SlideShare. Like this presentation? Why not share! Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. Published in: Science , Technology , Business.
Full Name Comment goes here. Are you sure you want to Yes No. Show More. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Chapter 4b 1. Depletion Region Depletion region 5. Energy band diagrams for a pn junction under c reverse bias conditions. Light Emitting Diode I—V characteristic of a p-n junction. LED types Infrared - 1. Principles of LED Recombination around the junction and within the diffusion length of the electrons in the p-side leads to photon emission.
Kasap, Optoelectronics Prentice Hall Fig. Device structures GaAs or GaP as shown in Fig. Kasap,Optoelectronics Prentice Hall Fig. Band gaps of some common semiconductors relative to the optical spectrum.
Two types of blue LED materials 1. GaN is a direct bandgap semiconductor with Eg of 3. The less efficient type is the Al doped SiC, which is an indirect bandgap semiconductor — The acceptor type localized energy level captures a hole from the valence band — A conduction electron then recombines with this hole to emit a photon — As the recombination process is not direct and therefore not as efficient, the brightness of blue SiC LEDs is limited.
Hatched region and dashed lines are indirect Eg materials. The homojunction LED has two drawbacks. The p-region must be narrow to allow the photons to escape without much re-absorption — When p side is narrow, some of the injected electrons in the p side reach the surface by diffusion and recombine through crystal defects near the surface — The radiationless recombination process decreases the light output 2.
If the recombination occurs over a relatively large volume distance , due to long electron diffusion length, then the chances of re-absorption of emitted photons becomes higher. EF must be uniform. GaAs Schematic illustration of photons escaping reabsorption in the AlGaAs layer and being emitted from the device.
The rate of direct recombination is proportional to both electron and hole concentrations 1. The transition, which is identified as 1 in Fig 7 a , has the relative small intensity of light with photon energy hv1. The relative intensity of light corresponding to transition hv2 is maximum — The transitions that involve the largest electron and hole concentration occur most frequently.
The light intensity at the relative high photon energies hv3 occurred through transition 3 is small. The turn-on voltage is around 1. The band gap of GaAs at K is 1. You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips.
Visibility Others can see my Clipboard. Cancel Save.
Continue to access RSC content when you are not at your institution. Follow our step-by-step guide. Cubic phase zinc-blende GaN referred to as c-GaN -based phosphor-free white light emitting diodes LEDs can exhibit superior characteristics and ultrahigh efficiency compared with conventional hexagonal phase wurtzite GaN referred as h-GaN -based examples. However, one notorious issue is low quality of c-GaN due to thermodynamical instability of cubic phase, epilayer-substrate chemical incompatibility, and large lattice-mismatch during epitaxial deposition, giving rise to insufficient light emission efficiency. Here, we report the growth of high quality single crystalline GaN microcubes MCs with pure zinc-blende phase for large scale production by the chemical vapor deposition method.