It is shown theoretically that for certain profiles of inhomogeneity along the electric field of the density of the rate of photogeneration of carriers in semiconductors, three unexpected effects can ...appear. These are self-amplification and self-extinguishing of the density of the photogeneration rate of carriers and self-inversion of its sign. The effects are due to the local photoinduced space charge. The shapes of the profiles depend on the parameters of the semiconductor, the strength of the electric field, and the temperature. Examples are given for all three types of profiles.
A concept of profile photoelectronics is introduced. A photoresistor is used as an example to present the basic principles of this new promising branch of photoelectronics. It is based on specific ...profiling of the shape of the incident radiation flux relative to the direction of the electric field. The possibility of new anomalous photoelectric effects in semiconductors is theoretically shown. They are called self-amplification of incident radiation, self-quenching, and self-inversion of the sign of the photogeneration rate (generation of negative photoconductivity). Specific examples are provided for all three types of profiles. The results of the analysis fundamentally change the existing concepts of possible photoelectric effects in semiconductors. Such results open up prospects for development of a new generation of photodetectors for weak optical and short-wavelength radiation.
It is shown theoretically that the effective rate of carrier photogeneration in a longitudinal photoresistor, which directly initiates the conversion of the radiation into the electric current, can ...be positive, zero, or negative and significantly exceed the true carrier photogeneration rate in absolute value. The effects are shown to be caused by the photoinduced local space charge.
In this paper, we analyze the intrinsic photoconductivity burst of semiconductors at an increase in the recombination center concentration upon uniform and non-uniform weak illumination along the ...electric field. An equation for the concentration distribution of nonequilibrium carriers at an arbitrary illumination profile along the electric field is derived without using the quasi-neutrality approximation. Based on this equation, the bursts in photoelectric gain of the transverse and longitudinal photoresistors should significantly differ from each other under any recombination conditions at current contacts due to the photo-induced space charge. If the carrier photogeneration is not uniform, then, unlike uniform photogeneration, the photoelectric gain burst depends on the polarity of the applied voltage. The quasi-neutrality approximation does not produce these results. An analytical expression for the maximum value of the electron photoelectric gain depending on the recombination center concentration is derived in the case of an exponential photogeneration profile and pulling-out contacts. The relationship that was found between the concentrations of nonequilibrium electrons and holes allows derivation of an analytical expression for the maximum value of the hole photoelectric gain.
In this paper, we derive an analytical expression for the multiplication factor of photocarriers in avalanche heterophotodiodes with separated absorption and multiplication regions. The ...multiplication factor is presented in the traditional Miller form. The dependence of this factor on the applied bias voltage and heterostructure parameters is analyzed.
The geochemical typification of magmatic rocks of the Mankhambo block (southern part of the Lyapinsky anticlinorium), which is confined to the junction zone of the Ural orogen with the ...Timanide–Cadomide belt relics, was performed based on the generalization of abundant isotope-geochemical data, application of modified discriminant diagrams, and analysis of Y/Nb ratio. The magmatic rocks mark two stages of the geodynamic evolution of this structure. The first stage (RF
2–3
) is characterized by the tholeiitic magmatism (subvolcanic basic rocks of the Shchokuryinsky and Moroinsky complexes). According to composition and source type (Y/Nb = 3–5, E-MORB), these rocks can be correlated with riftogenic plume-related series of the East European passive margin. Magmatism of the second stage (650–500 Ma) was related to the evolution of divergent transform continental margin. This stage involved the subsequent formation of calc-alkaline magmatic series (653–608 Ma) (Sys’insky and Parnuksky complexes) and bimodal basalt–rhyolite association (569–554 Ma) (Sablegorsky and Laptopaisky complexes), which vary from tholeiitic to calc-alkaline rocks. High values of the Y/Nb ratio (5–8) in the basic rocks of the Sablegorsky complex suggest that their generation was related with intensification of transform movements, when plume-related basic magma (E-MORB-type source) interacted with more depleted slab-derived component. The rhyolites of the Sablegorsky complex mark the incipient generation of the A-type rhyolite–granite association (Y/Nb = 0.2–1), which was continued (522–490 Ma) by the granites of the Mankhambo and Ilya-Iz massifs. Their genesis may be related to the differentiation of magmas from two possible sources. A-granites with Y/Nb = 2.0 (phase I of the Mankhambo massif) were generated from E-MORB-type source. Granites of phase II (Y/Nb = 0.2–1) were derived from heterogeneous sources with the participation of OIB-type component. In general, the rocks of the Vendian–Cambrian stage, in comparison with older rocks, are characterized by the highest degree of plume-lithosphere interaction, with contribution of subduction-modified lithospheric mantle. The role of crustal contamination increases from the rhyolites of the Sablegorsky and Laptopaisky complexes to the granites of the Mankhambo massif. The presence of relict zircons and the “crustal” Sr and Hf isotope signatures indicate the contribution of ancient crustal material in their protolith. The genesis of the rhyolite–granite association may be associated with the emplacement of the “Mankhambo” plume. The plume role in the magma generation of rocks of the Mankhambo block increases with decreasing age.
A double heterostructure based on direct-gap semiconductors with a photoabsorption middle layer at the avalanche breakdown voltage is considered. Such structures are used in the development of ...avalanche photodiodes with separate absorption and multiplication regions (APD with SAMR). It is shown that impact generation of electron–hole pairs should be considered in calculating the maximum possible characteristics of APDs with SAMR even in the absorption layer; therewith, this can be performed analytically.
Naphtha fractions of the West Siberian gas condensate were evaluated as feedstock for thermal pyrolysis performed in the temperature interval 750–900°C at the conventional contact time of 0.2–0.4 s ...and steam-to-feed weight ratio of (0.5; 0.8): 1.0. Statistical models of the process, based on the experimental dataset obtained, were constructed and used for multicriteria optimization with respect to the key products: ethylene, propylene, divinyl, pyrogas, and coke. The optimum process parameters for pyrolysis of light and heavy naphtha of the gas condensate to reach the maximal yield of target products (ethylene, propylene, divinyl) under the conditions of compromise solutions were found. The influence of the group and individual hydrocarbon composition of the naphtha fractions of the gas condensate on the yield and distribution of the major products was demonstrated.
This paper deals with the second part of the overview on analytical calculations of the characteristics of avalanche photodiodes (APDs) based predominantly on direct gap semiconductors. In the first ...part of the overview (JCTE 2017, vol. 62, no. 9, p. 1027), a general formulation of the problem is carried out and an approach to its solution is reported. The program for calculations of multiplication coefficientins is fulfilled. In the most typical situations, they are represented analytically. It is demonstrated that the obtained analytical results are in good quantitative agreement with previously published numerical calculations and experimental data. In the given part of the overview, the dependences between the interband tunnel current of the heterostructure with a
p
+
–
n
junction in the “wide-gap” (wg) layer and the parameters of used semiconducting materials, layer-doping levels, and their thicknesses corresponding to avalanche breakdown voltages of a heterostructure are analyzed theoretically. It is demonstrated that, as a rule, the tunnel current depends nonmonotonically on the dopant concentration in the “high-resistance” region of a wg layer. There is an optimal concentration of the given dopant at which the tunnel current reaches its absolute minimum. Simple formula for determining the optimal concentration is derived. In addition, an analytical expression for determining the minimum tunnel current is obtained. In real cases, tunnel currents can vary by several orders of magnitude. It is found that, in many cases, an increase in the doping level of a “narrow gap” layer diminishes the tunnel current. It is shown that the tunnel current does not vanish with a decrease in the doping level of the high-resistance layers of a heterostructure but, beginning with a certain concentration, becomes independent of the doping level. An analogous effect is inherent to a homogeneous
p
+
–
n
junction. Physical reasons of such behavior of tunnel currents, which are observed at an avalanche breakdown voltage, are discussed. A technique for the optimizing the parameters of the APD heterostructure with separate absorption and multiplication regions (SAMRs) is developed. As an example, specific calculations are carried out for a widely used InP–In
0.53
Ga
0.47
As–InP heterostructure. The opportunity of description of transient phenomena in
p–i–n
APDs is considered first of all in the case where the initial voltage
V
0
is higher than the avalanche breakdown voltage
V
BD
. This problem is formulated because there is a need to know the explicit conditions whereby the Geiger mode is generated in APD operation. A formula describing the total time of progress in the avalanche Geiger process is derived. An analytical expression for the implementation of the Geiger mode is presented. At the end of the given paper, the advantages of avalanche heterophotodiodes with SAMRs of the low-high-low type over classical samples are demonstrated and discussed on the basis of analytical calculations. The numeration of formulas, figures, and references continues that used in Part I.
The analytical model of avalanche photodiodes based on the different types of
p–n
structures is discussed. Formulas for avalanche breakdown voltage
V
BD
and the exponent in Miller’s relation for ...dependence between the carrier multiplication coefficient
M
and the applied voltage
V
are derived. The obtained results enable us to avoid time-consuming numerical calculations and develop an analytical method for optimizing the structural parameters of avalanche heterophotodiodes (its principles will be reported in Part II).
