Semiconductors reflection coefficient

Because of these factors, the fundamental experimental information about the interaction of metastable atoms with semiconductors and dielectrics is meant for the reflection coefficients that are determined with the aid of beam methods and for the coefficients of heterogeneous deactivation which are evaluated under diffusion conditions. However, the data in this event are fairly scarce and conflicting. The results obtained by the methods of electronic beams do not agree with diffusion experiments. Thus, Allison et al [ 137] report that the coefficients dealing with... 

In the EER method, the relative variation of the optical reflection coefficient (AR/R) of the electrode surface caused by the low-frequency harmonic modulation of the electrode potential is used as the informational signal [96-98]. The high sensitivity of EER technique (it is possible to detect the AR/R values of about 10 5-10 7) allow us to identify the impurity electronic levels in a semiconductor band gap at their very small concentrations and, therefore, to control the actual surface energy states rather than those distributed in the sub-surface region [49-57]. 

Growth of multilayer periodic Z nS/ZnSe h eterostructures b y m etallorganic c hemical vapor deposition, their optical properties examined by ellipsometry and traditional spectroscopy are described. The results obtained evidence that the structures proposed are promising as efficient Bragg reflectors for blue semiconductor lasers. Reflection coefficient higher than 90% in the blue-green spectral range have been obtained. 

The photoconductor, as shown in Fig. 7, depends upon the creation of holes or electrons in a uniform bulk semiconductor material, and the responsivity, temporal response, and wavelength cutoff are unique to the individual semiconductor. An intrinsic photoconductor utilizes across-the-gap photoionization or hole-electron pair creation. An extrinsic photoconductor depends upon the ionization of impurities in the material and in this case only one carrier, either hole or electron, is active. The same is true for a quantum-well photoconductor, in which electrons or holes can be photoexcited from a small potential well in the narrower band-gap regions of the semiconductor. The quantum efficiency for the structure in the figure is determined by the absorption coefficient, o, and may be written 2isrj = (l — / )[ — where R is the reflection coefficient at the top surface. Carriers produced by the radiation, P, flow in the electric field and contribute to this current flow for a time, r, the recombination time. The value of the current is... 

The absorptive active region (for MWIR and LWIR devices typically fabricated from a narrow-bandgap material, its thickness d and the absorption coefficient a) is positioned between two layers of wider-bandgap material (thickness Li and and the absorption coefficient of both layers ttex). DBR mirrors are on the top and the bottom side. In some cases the top Bragg mirror does not exist, and its role is assumed by the interface between semiconductor and the incident medium (air), which furnishes a top surface reflection coefficient of about 30 % [251]. 

Basic physical properties of sulfur, selenium, and tellurium are indicated in Table 1.3. Downward the sulfur sub-group, the metallic character increases from sulfur to polonium, so that whereas there exist various non-metallic allotropic states of elementary sulfur, only one allotropic form of selenium is (semi)metallic, and the (semi)metallic form of tellurium is the most common for this element. Polonium is a typical metal. Physically, this trend is reflected in the electrical properties of the elements oxygen and sulfur are insulators, selenium and tellurium behave as semiconductors, and polonium is a typical metallic conductor. The temperature coefficient of resistivity for S, Se, and Te is negative, which is usually considered... 

The method of semiconductor sensors allows one to determine the flux of atoms, to which the sensor was exposed, from electric conductivity measurements (provided coefficients of ionization and reflection of oxygen atoms from zinc oxide films are known). In other words, the sensor technique can be used in this case as an absolute method [21]. Indeed, variation of electric conductivity of a semiconductor film Acrpi due to adsorption is known to be caused by variation of carrier concentration An in the film, rather than by variation of their mobility / [21] ... 

Electrons in metals and semiconductors give rise to free-carrier absorption, the absorption coefficient being proportional to the square of the incident wavelength (hence high in the infrared region for most metals). The reflectivity of metals is related to the plasma frequency, cOp, by the relation... 

At this point it should be noted that both the index of refraction and the extinction coefficient are extremely frequency dependent. Consequently, the properties of absorption, reflection, and phase shift which depend on them will also show a frequency dependence. Value of r] and k for most metals and semiconductors are tabulated in the American Institute of Physics Handbook ... 

The reflectance depends upon the K/S ratio and not on the absolute values of K and S. The scattering S coefficient is independent from the wavelength over wide spectral ranges and therefore the SKM function reflects the trend of the absorption K coefficient. Moreover, because SKM is a function of a(hv), a plot of (F(RJj against hv can be used to determine f g in powdered semiconductor oxides. 

Infrared spectroscopy (IR) is a fairly simple in situ method. Since the absorption coefficients of molecular vibrations are rather low, it is impossible to detect the IR absorption of a molecule adsorbed or bonded to the semiconductor surface, merely by an ordinary vertical transmission measurement. This problem was solved by using attenuated total reflection (ATR) spectroscopy, as introduced by Harrick [17], and first applied to semiconductor-liquid junctions by Beckmann [18,19]. In this technique, the incident IR light beam is introduced via a prism into a semiconductor, at such an angle that total internal reflection occurs at the semiconductor-liquid interface, as illustrated... 

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