W Spontaneous recombination based on quantum mechanics was discussed by Bebb and Williams (1972), Agrawal and Dutta (1986), Dutta (1993), Thompson (1980), and others. The quantum mechanical calculation for the spontaneous emission rate is based on the induced emission rate given by Fermi’s Golden Rule which gives the transition probability per unit time (called transition […]

In this chapter, the theory of radiative recombination is first discussed in terms of a rigorous quantum mechanical model. Subsequently recombination is discussed in terms of a semi- classical model based on equilibrium generation and recombination. This model was developed by van Roosbroeck and Shockley (1954). Finally, the Einstein model of spontaneous and stimulated transitions […]

So far we have seen that several mechanisms for non-radiative recombination exist, including Shockley-Read, Auger, and surface recombination. Even though non-radiative recombination can be reduced, it can never be totally eliminated. For example, surface recombination can be drastically reduced by device designs that spatially separate the active region from any surfaces. However, even if the […]

There are two basic recombination mechanisms in semiconductors, namely radiative recombination and non-radiative recombination. In a radiative recombination event, one photon with energy equal to the bandgap energy of the semiconductor is emitted, as illustrated in Fig. 2.5. During non-radiative recombination, the electron energy is converted to vibrational energy of lattice atoms, i. e. phonons. […]

Quantum wells provide a means of confining the free carriers to a narrow quantum well region by using the two barrier regions cladding the quantum well. Assume that the well region has a thickness of LqW. Assume further that the conduction band and valence band wells have carrier densities of n2D and p2D, respectively. The […]

Next, we discuss the recombination dynamics as a function of time. Consider a semiconductor subjected to photoexcitation. The equilibrium and excess electron and hole concentrations are n0, p0, An, and Ap, respectively. Since electrons and holes are generated and annihilated (by recombination) in pairs, the steady-state electron and hole excess concentrations are equal, A n(t) […]

Any undoped or doped semiconductor has two types of free carriers, electrons and holes. Under equilibrium conditions, i. e. without external stimuli such as light or current, the law of mass action teaches that the product of the electron and hole concentrations is, at a given temperature, a constant, i. e. (2.1) n0 P0 = […]

Electrons and holes in semiconductors recombine either radiatively, i. e. accompanied by the emission of a photon, or non-radiatively. In light-emitting devices, the former is clearly the preferred process. However, non-radiative recombination can, under practical conditions, never be reduced to zero. Thus, there is competition between radiative and non-radiative recombination. Maximization of the radiative process […]

As devices with higher power capabilities have become available, new application areas emerge constantly. Figure 1.14 shows the use of LEDs integrated into medical goggles worn by a surgeon during an operation (Shimada et al., 2003). The LED-based light source promises substantial weight savings and fulfills the stringent requirements of high-quality color rendition required during […]

The AlGaInP material system is suited for high-brightness emission in the red (625 nm), orange (610 nm) and yellow (590 nm) spectral range and today is the dominant material system for high-brightness emitters in that wavelength range. Figure 1.13 shows some of the common signage applications of red and yellow AlGaInP LEDs. The AlGaInP material […]