Indirect bandgap semiconductor

Diamond, however, is not the universal semiconductor panacea it is an indirect bandgap semiconductor and does not lase. In addition, present semiconductor materials, such as silicon and gallium arsenide, are solidly entrenched with a well-established technology, and competing with them will not be an easy task. CVD diamond will also compete with silicon carbide, which has also an excellent potential as a high-performance semiconductor material and is considerably easier and cheaper to produce. 

Figure 7.6 Schematic representation of fundamental absorption processes in (a) direct bandgap and (b) indirect bandgap semiconductors. Phonon emission and phonon absorption processes are marked in red. (Adapted from Yacobi [211)...

The n parameter equals 1 for direct bandgap semiconductors or 4 for indirect bandgap semiconductors in the case of allowed fundamental transitions [22], Other values of n, 2 or 3, are valid only for forbidden transitions. The proper transformation allows estimation of the bandgap energy, Eg, for both types of crystalline semiconductors. Figure 7.7 presents the procedure of Eg evaluation. 

In indirect bandgap semiconductor crystals both the emission and absorption of phonons are allowed to preserve the momentum (see Figure 7.6.). Therefore two contributions to the overall absorption spectrum should be considered aa and ae, associated with phonon absorption and emission, respectively [21] ... 

Figure 7.9 Recombination of electrons and holes in the case of (a) direct bandgap semiconductor and (b) indirect bandgap semiconductor. The energy E is a function of the wave vector k...

Cubic boron nitride has high thermal conductivity, high dielectric constant, great hardness, and good chemical stability. The material can be doped n-type with Si and p-type with Be to form p-n junctions. While cubic boron nitride (c-BN) has been successfully doped p- and n-type to produce the first UV-LEDs, it is an indirect bandgap semiconductor which will ultimately limit emission efficiency. Relatively few studies have been performed on this material system. ECR-LPCVD techniques [23, 24] and LPCVD [25] have had the most success informing BN films. As with other specialty materials there is a lack of BN substrates. In order to produce the c-BN phase, high deposition temperatures often are combined with assisted techniques. 

FIGURE 3 Energy vs. momentum band diagram for an indirect bandgap semiconductor (Er - Ex > ksT). Phonons are involved in the recombination of the holes from the valence band with the electrons in the X valley of the conduction band. 

Dopants with energy levels closer to the center of the energy gap (i.e., the so-called deep energy level dopants) serve as electron-hole recombination sites, impacting the minority carrier lifetime and the dominant recombination mechanism in indirect bandgap semiconductors. 

The semiconductor properties of diamond are excellent and it has good potential as a semiconductor material. i It is an indirect bandgap semiconductor and has the widest bandgapof any semiconductor (see Sec. 6.2). 

Direct-Bandgap Semiconductor see Indirect-Bandgap Semiconductor. 

We saw in Chapter 20 that direct or vertical interband transitions from a full band to an empty band were possible even in indirect bandgap semiconductors provide the photon energy liw = EgmptyW Efuii ( )- Similar interband transitions occur in metals where electrons can be excited from full bands below the Fermi level to empty bands just above the Fermi level or from full bands just below the Fermi level to empty bands above the Fermi level as illustrated in Figure 24.15. The flat d-bands in Cu lie a couple of volts below the Fermi level and transitions from these bands to the empty parabolic s-bands just above the Fermi level are responsible for the loss of copper s reflectance in the visible spectrum. 

At equilibrium in the dark. Equation 5.6 holds. Application of either a bias or illumination increases norp (or both). For a direct bandgap semiconductor, transitions between the conduction and valence bands involve only the absorption/emission of photons. Transitions between the conduction and valence bands in indirect bandgap semiconductors require both absorption/emission of photons and phonons (lattice vibrations). Since both energy and momentum must be conserved, direct band-to-band transitions in indirect bandgap semiconductors are much less probable because of the additional requirement of momentum conservation, and so values of k tend to be much smaller than for direct bandgap semiconductors. 

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