Semiconductor Light-Emitting Diodes

Inorganic semiconductor light-emitting diodes (LEDs) 181000000... 

The physical mechanism by which semiconductor light-emitting diodes (LEDs) emit light is spontaneous recombination of electron-hole pairs and simultaneous emission of photons. The spontaneous emission process is fundamentally different from the stimulated emission process occurring in semiconductor lasers and superluminescent LEDs. The characteristics of spontaneous emission that determine the optical properties of LEDs will be discussed in this section. 

A method of white light illumination uses the electroluminescence of semiconductor light-emitting diodes (LEDs), either singly or by the combination of red, green, and blue emitting diodes. However, white organic LEDs suffer from relatively short... 

Fig. 6.6 A semiconductor light-emitting diode (LEDs). The p-n junction is forward-biased (by connecting positive voltage to a p type p semiconductor and negative voltage—to a n-type semiconductor) and the external electromagnetic field has a polarity opposite to the internal field in the semiconductor. Therefore, the resultant field is small and the p-n junction conducts electric current. This enables continuous injection of electrons (e) from the n-type semiconductor to the p-type semiconductor and their recombination with electron holes (h) resulting in an emission of photons of an energy hv...

Interest in AIN, GaN, InN and their alloys for device applications as blue light-emitting diodes and blue lasers has recently opened up new areas of high-pressure synthesis. Near atmospheric pressure, GaN and InN are nnstable with respect to decomposition to the elements far below the temperatures where they might melt. Thus, large boules of these materials typically used to make semiconductor devices caimot be grown from the... 

Semiconductors are materials that are characterized by resistivities iatermediate between those of metals and of iasulators. The study of organic semiconductors has grown from research on conductivity mechanisms and stmcture—property relationships ia soHds to iaclude appHcations-based research on working semiconductor junction devices. Organic materials are now used ia transistors, photochromic devices, and commercially viable light-emitting diodes, and the utility of organic semiconductors continues to iacrease. 

Light-emitting diodes are the most commercially important compound semiconductor devices in terms of both doUar and volume sales. The 1991 worldwide compound semiconductor device market totaled 2.8 biUion (39). Light-emitting diodes accounted for ca 1.9 biUion of this market. Visible and ir LEDs represented 37 and 30%, respectively. These markets are expected to grow as LEDs are increasingly employed in advanced appHcations. 

A light-emitting diode (LED) is a forward-biasedp—n junction in which the appHed bias enables the recombination of electrons and holes at the junction, resulting in the emission of photons. This type of light emission resulting from the injection of charged carriers is referred to as electroluminescence. A direct band gap semiconductor is optimal for efficient light emission and thus the majority of the compound semiconductors are potential candidates for efficient LEDs. 

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