Band gap energy, estimation

The band gap energy has been discussed from the photo-current action spectrum. The band gap energy estimated from the photo-cmrent spectra is abont 2 eV for the assumption for the indirect photo excitation process. We can illustrate a model of the band diagram of n-type semiconductive passive oxide for the photo-induced process in Fig. 38. The indirect transition may pos-... 

The potential of cBN as a semiconductor was also shown by Wentorf (4). cBN can be regarded as the extreme of III-V compounds from the viewpoint of periodic table systematics. Indeed, its band gap energy (estimated to be 6.3 eV see Sec. III.A) is the widest among known semiconductors including diamond. This fact gives us a hint that cBN has new potential in electronic applications. 

Band-gap energies between 1.45 eV and 1.47 eV were obtained for the films. The band-gap energies were estimated using plots of (ahv)2 versus E (Fig. 6.23), where a is an absorption coefficient estimated from optical transmittance data and hv is the photon energy. Figure 6.23 shows that the band edge... 

EXAMPLE 4.3 Figure 4.9(a) shows the dependence of the absorption coefficient versus the photon energy for indium arsenide, (a) Determine whether or not InAs is a direct-gap semiconductor, (b) Estimate the band-gap energy, (c) If an InAs sample of 1 mm thickness is illuminated by a laser of 1 W at a wavelength of 2 jam, determine the laser power for the beam after it passes through the sample. Only consider the loss of light by optical absorption. 

The data in Table 3.16 may be used to estimate the band gap energy for unstrained wurtzite-structure MgO of E = 6.9 eV and for rocksalt-structure ZnO of Ee — 7.6 eV, with stronger bowing for the rocksalt-structure than for the wurtzite-structure occurrence of the alloys. Theoretical band-structure calculations for ZnO revealed the high-pressure rocksalt-structure phase as... 

With the knowledge of the quasi-Fermi level of electrons, the level of holes can be estimated by adding the band-gap energy as obtained from diffuse reflectance spectra. This rough but helpful procedure is based on the assumption that both Fermi levels are located very close to the corresponding band edges. Since most of the employed powders represent highly doped semiconductors, this seems a reliable approximation. 

Correlation between electrochemical and spectroscopic data usually focuses on the determination of band gap energy and the estimation of the position of upper edge of the valence band (HOMO energy) and the lower edge of the conduction band (LUMO energy). Formal electrode potentials are correlated to the vacuum level as previously indicated. In most cases, the corresponding energies, Fhomo ... 

Figure 17-9. Diagram depicting the redoxpotentiak ofvtdence and conduction bands, and band-gap energies for various metal oxides estimated at pH 7. The redox potential positions of...

From the intercept the Sg is estimated to be 2.6 eV. Searson et al. replotted the absorption coefficient estimated from the data in Fig. 24 in (ahvf = (Av -sae) to evaluate the band gap energy of 1.75 eV for the indirect transition. Such band gap energy has been evaluated from the photo-excited cd measured as a function of photon energy under an assumption that the cd was proportional to the absorption coefficient. The absorption edge was estimated from the photo-excited cd to be a range from 2 to 3 eV. " The photo-excited current will be discussed in the following section. 

Fig. 20 (Absorbance/A,) vs. 1/X, plot for CdTe nanoparticles with estimated band gap energy using...

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