Structure and bonding in narrow gap semiconductors

Many trends in the behavior of elements and their compounds are immediately visible by comparison with their position in the periodic table. The most obvious trend is that the elements to the left and in the lower part of the periodic table are metals while the rest are covalently-bonded semiconductors or insulators; the coordination number of the covalently-bonded materials is generally given by the 8-N rule (N is the column number). The next clear trend comes in the consideration of binary compounds; here we find that the horizontal separation of the two elements in the periodic table is a good indication of their ionicity. For example, this explains the trends in the forbidden energy gap and the crystal structure along an isoelectronic series (e.g. KBr, Case, ZnSe, GaAs, Ge).     

Avalanche breakdown in narrow gap semiconductors in crossed fields

The paper presents the results of experimental and theoretical investigations of interband breakdown in narrow gap Bi_1?xSb_x and Hg_1?xCd_xTe semiconductors in crossed electric and magnetic fields. Both these alloys show an increase of breakdown electric field in sufficiently strong magnetic field. In the case of Hg_1?xCd_xTe the breakdown field changes nonmonotonically with H. This is interpreted as being due to the transverse breakdown.     

Band gap engineering of atomically thin two-dimensional semiconductors

Atomically thin two-dimensional(2D) layered materials have potential applications in nanoelectronics, nanophotonics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for their broad applications in high-performance integrated devices, such as broad-band photodetectors, multi-color light emitting diodes(LEDs), and high-efficiency photovoltaic devices. In this review, we will summarize the recent progress on the controlled growth of composition modulated atomically thin 2D semiconductor alloys with band gaps tuned in a wide range, as well as their induced applications in broadly tunable optoelectronic components. The band gap engineered 2D semiconductors could open up an exciting opportunity for probing their fundamental physical properties in 2D systems and may find diverse applications in functional electronic/optoelectronic devices.     

IR optical absorption and reflection spectra in narrow gap semiconductors

Light transmission T(λ) and reflection R(λ) spectra were measured for the crystals Cd_xHg_1−xTe (x = 0.26). InSb and Mn_xHg_1−xTe (x = 0.12) with low impurity content at T = 300 K in the wavelength range 2.5 μm ⩽ λ ⩽40 μm. From the measured T(λ) and R(λ) data a dependence of the absorption coefficient x(λ) for the free-carriers light absorption (FCLA) was derived, which is caused by the intrabund electron and hole transitions and the intcrband transitions of the heavy holes from the band V₁ to the band V₂ of the light holes: x(λ) = x_intraband(λ) + x_interband(λ).It is concluded from the quantum mechanical approach that the intraband FCLA is directly related with the carriers scattering mechanisms. Calculations of x_intraband(λ) within the framework of this approach demonstrated that under room temperature the major contribution was from the scattering by polar optical phonons. In the case of less perfect Mn_xHg_1−xTe however, one should take into account the scattering by the short-range potentials of the defects.     

窄禁带半导体的非线性极化率和光学双稳性

本文改进了半导体两带模型,计算了窄禁带半导体的非线性极化率.运用所求得的极化率,研究了InSb的光学双稳性,所得到的稳态曲线、临界开关光强与入射光频率的关系以及动态特性都与实验结果有较好的符合.     

Mechanism of phase conjugation via stimulated Brillouin scattering in narrow band gap semiconductors

We develop a theoretical model to study optical phase conjugation via stimulated Brillouin scattering (OPC-SBS) in narrow band gap transversely magnetized semiconductors. Threshold value of pump electric field and reflectivity of the image radiation for the onset of OPC-SBS are estimated. The analysis is applied to both cases viz. centrosymmetric (CS) and non-centrosymmetric (NCS) crystals. Numerical estimates made for n-type InSb crystal at liquid nitrogen temperature duly irradiated by nanosecond pulsed 10.6 μm CO₂ laser shows that high OPC-SBS reflectivity (90%) can be achieved in NCS crystals at moderate pump electric fields if the crystal is used as an optical waveguide with relatively large interaction length (L = 5 mm) which proves its potential in practical applications such as fabrication of phase conjugate mirrors.     

On magnetic quantum oscillations of the Auger transition rate in narrow gap semiconductors

The experimental results of Dornhaus et al. on the dependence of the Auger recombination time on an applied magnetic field are explained within the frame of Takeshima's model by a proper inclusion of non-parabolicity and spin-splitting of the conduction band.     

Band gap anomaly in ternary chalcopyrite semiconductors,the role of p-d hybridization

Summary The anomalous reductions in the energy band gap of the chalcopyrite semiconductors as compared to their relative binary analogs are estimated quantitatively by using a simple relation that involves quantum defect electronegativity scale and the average principal quantum number. The chemical and the structural contribution to this anomaly is discussed in details and it is shown that the relation can be easily extended to explain the variation in the band gap of some cross-substitutional alloys.

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Riassunto Le anomale riduzioni del gap di energia nei semiconduttori a struttura calcopirite rispetto ai loro analoghi binari sono stimate quantitativamente usando una semplice relazione che implica l’uso della scala delle elettronegatività e il numero quantico principale medio. Il contributo chimico e strutturale a questa anomalia è discusso ed è mostrato che la relazione può essere agevolmente estesa per spiegare la variazione del gap in alcune soluzioni solide.

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Резюме Количественно оцениваются аномальные уменьшения ширины запрещенной зоны в полупроводниках халькопирита, по сравнению с бинарными аналогами. Подробно обсуждается химичекий и структурный вклад в эту аномалию. Показывается, что предложенный подход можно легко обобщить для объяснения изменения ширины запрещенной зоны в некоторых кросс-замещенных сплавах.

     

Band gap dependence with temperature of semiconductors from solar cells electrical parameters

Using experimental measurements of the open-circuit voltage and the short-circuit current density at different temperatures, for a solar cell, we investigate numerically the band gap evolution with temperature for the semiconductor constituting the concerned device. The application of the approach in the case of silicon semiconductor gives satisfying results compared to previous works.     

A simple approximative method for determination of Auger 1 lifetime in degenerate narrow gap semiconductors

Using the well-known Beattie-Landsberg expression for Auger 1 lifetime and the “effective” Auger energy gap (E_gA), we obtained a simple approximative expression for determination of the Auger 1 lifetime. We also obtained a formula for the electron concentration above which the effects of degeneration are significant.     

Electrophonon resonance in narrow band semiconductors

The theory of the electric current splashes on a current-voltage characteristic due to the phonon-induced-electron-transitions between Stark ladder levels is developed. Splitting and broadening of the current peaks because of an electric field vector deviation from the [ 111 ] direction is considered. The recent experimental results on current-voltage characteristic of the tellurium cluster superlattice in ceolite are accounted for by the electrophonon resonance studied in the present paper.     

Phase-modulation-induced two-wave mixing in semiconductors

Two-wave mixing amplification of a weak probe beam interfering with a powerful pump beam of the same linear polarization is demonstrated when the probe beam enters the semiconductor sample before the pump pulse. This mixing of two beams of the same frequency is made possible by the difference between self-phase modulation and cross-phase modulation, which modify differently the instantaneous frequencies of both beams. Net gain coefficients up to 5.5 cm (-1) are obtained for experiments performed in CdTe. Theoretical calculations quantitatively confirm this interpretation and predict much higher gain for more resonant configurations or higher pump energies, making this process of potential interest for optical processing.     

Highg-factors and Landau level crossing in the valence band of narrow gap semiconductors

When the Kildal-Bodnar [1–3] model of cadmium arsenide is developed for the valence bands, it is found that, for a range of energy below the band maximum, the spin splitting of Landau states is larger than the separation between Landau levels. The same holds for a variety of inverted-gap materials of Kane type [4–5] (with three-dimensional symmetry), as well as Kildal type (with axial symmetry). This could have interesting consequences for interband optical properties of Cd₃As₂ as well as for other p-type materials.     

One-photon absorption in direct gap semiconductors

One-photon absorption coefficients of InSb and GaAs are calculated using the first order perturbation theory assuming a two band model in which the interband energy difference is given by $E(k)=E_g{(1+\frac{h^2{k}^2}{m^{*E}g})}^{1/2}$ The results obtained are in much better agreement with the experimental data than the results of first order perturbation calculations using parabolic bands.     

Impact ionization rate in direct gap semiconductors

In the framework of the 14-band k ? p model, the intensity of the impact ionization processes in direct gap semiconductors is studied and explicit expressions for the impact ionization rate are obtained. It is shown that the rate of the process near the threshold energy is determined by the sum of the isotropic and strongly anisotropic contributions. The former contribution is proportional to the cube of the distance from the threshold, whereas the latter is a quadratic one arising only because of the coupling with remote bands. The comparison of these contributions under averaging over the nondegenerate isotropic distribution of nonequilibrium electrons characterized by some effective temperature T* demonstrates that the cubic contribution rather than the commonly used quadratic one is dominant in the direct gap semiconductors with E _g<1?1.5 eV up to T* = 300 K. This should be taken into account in the calculations of the operating characteristics of the devices based on the avalanche multiplication of charge carriers.     

Excitons in direct band gap cubic semiconductors

Perturbation is applied to study of the Wannier-Mott excitons in direct band gap cubic semiconductors with a fourfold degenerate highest valence band. The fine structure of exciton energy levels is investigated. General formulae are derived for the matrix elements of the perturbation. From these expressions it is straightforward to obtain values of the fine structure splittings of the energy levels and the wave functions of corresponding staes in any order of perturbation theory. A comparison with results of previous works is made.     

Band mixing effect in semiconductor superlattices

The band mixing effect on the electronic and optical properties of semiconductor superlattices is studied within the framework of the empirical tight-binding model. It is found that the superlattice periodic potentials mix the bulk heavy hole, light hole and spin-orbit-split bands in the valence band states. As a consequence, the optical matrix elements associated with various valence-to-conduction subband transitions are very sensitive to the variation of the wavevector in directions parallel to the interface ( _t). We find that band mixing in conjunction with the exciton effect can account for the Δn≠0 forbidden transitions observed in several recent experiments.