The bandgap energy versus lattice constant of the AlGaInN material system is shown in Fig. 13.2. The AlGaInN material system spans a very wide range of wavelengths covering the deep UV, near UV, visible, and even the near infrared spectral range. Of the three binary semiconductors InN, GaN, and AlN, epitaxially grown GaN has been […]

13.1 The UV spectral range The ultraviolet-visible boundary is at about 390 nm, where the 1978 CIE eye sensitivity curve has a value of 0.1% of its maximum value. This chapter concentrates on materials issues of III-V nitrides, on devices emitting in the ultraviolet (UV, X < 390 nm), and on devices emitting in the […]

The forward current-voltage (I-V) characteristics of a blue GaInN, a green GaInN, and a red AlGaInP LED are shown in Fig. 12.19. The forward turn-on voltage scales with the emission energy, indicating a well-behaved characteristic. Closer inspection of the forward voltage (at 1 mA) of the green LED (Vf, green = 2.65 V) indicates that […]

Optical emission spectra of red AlGaInP and green and blue GaInN LEDs are shown in Fig. 12.16 (Toyoda Gosei, 2000). Comparison of the emission spectra reveals that the green LED has a wider emission spectrum than either the blue or the red LED. This can be attributed to the well-known difficulties of growing GaInN with […]

The improvement in luminous efficiency of visible-spectrum LEDs has been truly breathtaking. The advancement of LED efficiency can be compared to the advancement made in Si integrated circuits where the performance increase versus time has been characterized by “Moore’s law”. This “law” states that the performance of Si integrated circuits doubles approximately every 18 months. […]

Originally, LEDs were exclusively used for low-brightness applications such as indicator lamps. In these applications, the efficiency and the overall optical power of the LED are not of primary importance. However, in more recent applications, for example traffic light applications, the light emitted by LEDs must be seen even in bright sunlight and from a […]

Graded-index encapsulants consisting of several layers with different refractive indices were demonstrated by Lee et al. (2004). The layer of highest refractive index is in contact with the semiconductor chip. The outer layers of the encapsulant have lower refractive indices. Extraction efficiencies exceeding those with a constant refractive index can be attained by using such […]

Encapsulants have several requirements including high transparency, high refractive index, chemical stability, high-temperature stability, and hermeticity. All encapsulants are based on polymers, several of which are shown in Fig. 11.8. A simple polymer molecule consisting of a hydrocarbon chain is shown in Fig. 11.8 (a). Branching and cross linking the polymer molecule results in rubber […]

Electrostatic discharge (ESD) can be a major failure mechanism for electronic and optoelectronic components (Voldman, 2004). Consider that a charge +Q is brought into contact with one of the diode electrodes. Consider further that the charge +Q is discharged uniformly over a time At, so that a current of I = +Q / At flows […]

11.1 Low-power and high-power packages Virtually all LEDs are mounted in a package that provides two electrical leads, a transparent optical window for the light to escape, and, in power packages, a thermal path for heat dissipation. The chip-encapsulating material advantageously possesses high optical transparency, a high refractive index, chemical inertness, high-temperature stability, and hermeticity. […]