Infra-red properties of bulk heavily doped silicon

Summary In this work reflectance (R) and thermoreflectance (TR) spectra in the infra-red of bulk P and B heavily doped silicon samples are reported and discussed. The values of the scattering time and of the effective mass, as well as the temperature derivative of the plasma frequency, scattering time and high-frequency dielectric constant are extracted from the data and analysed in terms of free-carrier-photon and free-carrier-impurity interaction.

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Riassunto In questo lavoro sono riportati e discussi gli spettri di riflettanza (R) e termoriflettanza (TR) in infrarosso di campioni di silicio drogati pesantemente per diffusione con P e B. Dai dati sono ricavati i valori dei tempi di rilassamento e della massa effettiva, come pure la derivata in temperatura della frequenza di plasma, del tempo di rilassamento e della costante dielettrica ad alta frequenza, che sono analizzati sulla base delle interazioni fra portatori liberi e fononi e fra portatori liberi e impurezze.

     

Infrared characterization of silicon dioxide films obtained by chemical vapour deposition

Summary In this work we report new FTIR absorbance measurements due to Si−O stretching bond, Si−O−Si and O−Si−O bending bonds of silicon dioxide amorphous films. We compare the optical results obtained from films grown by APCVD, LPCVD, PACVD and thermal oxidation techniques. The effect of thermal annealing on optical obsorbance structures has been studied. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Infrared angular spectroscopy characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates

Summary In this paper the technique of infrared angular spectroscopy applied to the characterization of epitaxial layers ofn-type silicon grown on N⁺ or P⁺ substrates is illustrated. Some results are reported and discussed concerning films having a free-carrier concentration ranging from 10¹⁴ cm⁻³ to 10¹⁷ cm⁻³ and thickness of the order of 10 μm. A significant comparison with results obtained by other techniques (four-point probe, spreading resistance,C−V plots, etc.) is performed and a few simple conclusions are drawn. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Spectral, thermal and hardness studies on unidirectional grown dichlorido diglycine zinc dihydrate single crystal

Bulk semi-organic single crystal of dichlorido diglycine zinc dihydrate has been grown by unidirectional crystal growth method from aqueous solution. The phase of the grown crystal was identified using single crystal XRD analysis. The functional groups present in the crystal were confirmed using FTIR and ¹H NMR analysis. Transmission study shows 70% of transmission in the entire visible region, which reveals the good optical quality of the grown crystal. A stable broad peak in the range of violet-green emission was observed in the emission spectrum, which is due to the existence of defects in the crystal. The thermal and mechanical properties of the grown crystal were studied using TG/DTA and the Vickers microhardness tester, respectively.     

Decay from photo-excited doubly degenerate electronic levels. A simple interpretative approach

Summary A simple physical model for interpreting decay processes from excited doubly degenerate electronic levels is described. It considers different de-excitation channels on the potential energy surfaces in the two-dimensional space of the ε-type coordinates. The obtained results are then discussed and their relevance for photophysics and photochemistry is stressed.

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Riassunto Si descrive un semplice modello fisico per l'interpretazione dei processi di decadimento da livelli elettronici eccitati doppiamente degeneri. Esso prende in considerazione differenti canali di diseccitazione sulle superfici di energia potenziale nello spazio bidimensionale delle coordinate di tipo ε. I risultati ottenuti sono poi discussi e si sottolinea la loro importanza per la fotofisica e la fotochimica.

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Резюме Описывается простая физическая модель для интерпретации процессов распада из возбужденных двукратно вырожденных электронных уровней. Рассматриваются различные каналы девозбуждения на поверхностях потенциальной энергии в двумерном пространстве координат ε-типа. Обсуждаются полученные результаты и отмечается их значимость для фотофизики и фотохимии.

     

Two-photon interband transitions in semiconductors in a static magnetic field. Nonlocal effects

Summary It is shown that in the presence of a static magnetic field, the electronic states in the effective-mass approximation are described by a Hamiltonian containing a nonlocal potential. In order to preserve the gauge invariance of the transition rates, the interaction between the electrons and the radiation has to be modified. For ZnS, the transition rate between two particular levels is evaluated by showing a difference of more than one order of magnitude when compared with the transition rate previously calculated. Partially supported by the Italian Research Council (C.N.R.) through G.N.S.M.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

Normal- and oblique-incidence reflection of semi-infinite crystals: Adiabatic approach with excitonic effects

Summary Excitonic reflection spectra of semi-infinite crystals are calculated within Stahl's coherent wave approach to band gap dynamics. Stahl's constitutive equations are solved by an adiabatic approximation in a surface region of the thickness z₀ and exactly in the bulk. The depth z₀ determines a region where the repulsive surface potential plays a decisive part for the motion of electrons and holes. The method yields simple analytical expressions for the reflectivity and for the bulk polariton amplitudes both for the normal and for the oblique incidence. Calculated reflectivity curves are compared with experimental data for various semiconductors and various angles of incidence showing a fairly good agreement.

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Riassunto Si calcolano gli spettri di riflessione eccitonica di cristalli semi infiniti entro l'approccio d'onda coerente di Stahl alla dinamica dell'intervallo di banda. Le equazioni costitutive di Stahl si risolvono con un'approssimazione adiabatica in una regione di superficie di spessore z₀ ed esattamente nel volume. La profondità z₀ determina una regione in cui il potenziale di superficie repulsivo ha un ruolo decisivo per il moto degli electtroni e delle lacune. Il metodo rende semplici espressioni analitiche per la riflettività e per le ampiezze del polaritone di volume sia per l'incidenza normale che per quella obliqua. Si confrontano le curve di riflettività calcolate con i dati sperimentali per vari semiconduttori e vari angoli d'incidenza mostrando un accordo abbastanza buono.

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Резюме Вычисляются экситонные спектры отражения для полубесконечных кристаллов в рамках подхода когерентных волн Сталя к динамике ширины запрещенной зоны. Решаются конститутивные уравнения Сталя с помощью адиаватического приближения в поверхностной области для толщины z₀ и точно в объеме. Глубина z₀ определяет область, где поверхностный потенциал отталкивания играет суцественную роль для движения злектронов и дырок. Предложенный метод дает простые аналитические выражения для овоих случаев нормального и наклонного падения. Вычисленные кривые отражательной срособности сравниваются с экспериментальми данными для раэличных полупроводников и различнях углов падения. Обнаружено довольно хорошее соответствие.

     

Direct and indirect two-photon processes in semiconductors

Summary The expressions describing direct and indirect two-photon absorption in crystals are given. They are valid both near and far from the energy gap. A perturbative approach through two different band models is adopted. The effects of the nonparabolicity and the degeneracy of the energy bands are considered. The numerical results are compared with the other theories and with recent experimental data in ZnO and AgCl. It is shown that the dominant transition mechanisms are of the allowed-allowed type near and far from the gap for both direct and indirect processes. Permanent address: Physics and Mathematics Department, Faculty of Engineering, Ain Shams University, Cairo, Egypt.     

Investigation of doping in Si crystals by means of electroreflectance

Summary In this work the importance of electroreflectance is evidenced in two specific applications concerning studies of semiconductor surfaces: i) determination of junction depths and carrier profiles, ii) mapping of inhomogeneity curves of the carrier distribution on Si surfaces. New information in both cases is obtained and briefly discussed. Work partially supported by Progetto Finalizzato Energetica (Sottoprogetto Energia Solare) of consiglio Nazionale delle Ricerche.     

Calculated spectral weight function in aluminum

Summary The spectral weight function of aluminum has been calculated within the local-density approximation. The inclusion of the energy-dependent self-energy has been proved to be important in calculating the single-particle energies, that are in good agreement with experimental data. The main disagreement we found is at theX ₁ ⁻ level the calculated energy of which is too low. An appreciable lifetime broadening is found with small band dependence and almost parabolic trend as a function of energy.

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Riassunto Nel presente lavoro la funzione spettrale dell'alluminio è stata calcolata in approssimazione di densità locale, includendo i contributi dipendenti dall'energia all'autoenergia del sistema. Si trova un generale miglioramento dell'accordo con le energie sperimentali di particella singola. L'unico disaccordo si trova al puntoX ₁, la cui energia calcolata è troppo bassa. Infine si trova un andamento quasi parabolico della vita media in funzione dell'energia, con una piccola dipendenza dalla banda.

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Резюме Вычисляется спектральная весовая функция в алюминии, используя приближение локальной плотности. Доказывается, что учет энергетической зависимости собственной энергии является важным при вычислении одночастичных энергий. Обнаружено хорошее согласие с экспериментом для одночастичных энергий. Единственное расхождение получено для уровняX ₁, для которого вычисленная энергия оказалась слишком низкой. Обнаружено заметное квази-параболическое уширение времени жизни, как функции энергии, с небольшой зависимостью от зоны.

     

Nonlinear index of refraction in semiconductors

Summary Experimental work on light refraction in semiconductors suggests that there are two separate mechanisms by which the index of refraction becomes nonlinear: direct saturation, on the one hand, and the Burstein-Moss effect, on the other hand. We show that this picture is incorrect, since it was based on the usage of the Bloch equation. Electron systems are not Boltzmann systems and the appropriate Fermi-Dirac master equation leads to a saturation that differs from the saturation of the Bloch equation. We show, using a simple two-level system, that this result may look like the spin result in one extreme (phonon bottleneck saturation), while it shows the features of the Burnstein-Moss effect in the limit of small degeneracy of the upper level (Fermi saturation).

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Riassunto I lavori sperimentali sulla rifrazione della luce nei semiconduttori suggeriscono la presenza di due meccanismi separati grazie ai quali l'indice di rifrazione diventa non lineare: la saturazione diretta, da un lato, e l'effetto Burstein-Moss, dall'altro. Noi mostriamo che questo quadro non è corretto, in quanto basato sull'equazione di Bloch. I sistemi di elettroni non sono sistemi di Boltzmann e l'appropriata ?master equation? produce una saturazione differente da quella dell'equazione di Bloch. Si mostra, usando un semplice sistema a due livelli, che questo risultato assomiglia a quello di un sistema di ?spin? ad un limite estremo (saturazione fononica a collo di bottiglia), mentre mostra le caratteristiche dell'effetto Burstein-Moss nel limite di piccola degenerazione del livello superiore (saturazione di Fermi).

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Резюме Экспериментальная работа по преломлению света в полупроводниках предполагает, что существуют два различных механизма, благодаря которым преломление становится нелинейным: с одной стороны прямое насыщение, а с дуугой стороны эффект ъурштейна-Мосса. Мы показываем, что эта картина не является корректной, т.к.основана на использовании уравнения ълоха. Электронные системы не являются больцмановскими системами и соответствующее управляющее уравнение Ферми-Дирака приводит к насыщению, котрое отличается от насыщения уравнения Блоха. Мы показываем, используя простую двухуровневую систему, что этот результат похож на результат для спина в случае одного максимума, тогда как этот результат обнаруживает особенности эффекта Бурштейна-Мосса в пределе малой вырожденности верхнего уровня.

     

Interference in the photodissociation (photoionization) by two close-lying frequencies

Summary The problem of photodissociation (photoionization) by two close-lying frequencies (two modes of a laser or two different lasers) is examined. In the case of one bound state and one continuum the problem is solved analytically and the solution is used to show that the photodissociation (photoionization) yield is reduced due to the interference between the two competing channels (i.e. absorption from one or the other photon mode). It is also shown that the population flow into the continuum happens simultaneously with a relevant photon redistribution between the two modes.

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Riassunto Si studia il problema della fotodissociazione (fotoionizzazione) ad opera di due frequenze vicine. Nel caso di un solo stato legato accoppiato dalla radiazione ad un continuo, si ricava una soluzione analitica del problema. Tale soluzione è adoperata per mostrare che la resa del processo è ridotta a causa dell'interferenza fra i due canali competitivi (assorbimento di uno o dell'altro fotone). Si mostra anche che contemporaneamente al flusso nel continuo si verifica una ridistribuzione dei fotoni fra i due modi.

     

Size effect in the optical properties of small metallic particles: A solvable model for cubic symmetry

Summary A solvable tight-binding model for the electronic states of cubic crystals of arbitrary size is used to compute the real and the imaginary part of the dielectric function of metallic particles. Two types of microscopic processes are discussed: first-order transitions between electronic states and second-order transitions due to collisions with vibrational states and impurities. Interband and intraband transitions are both taken into account fors andp bands. The results display very strong size effects due to the lack of translational symmetry and to the presence of surface states; the Lorentz-Drude behaviour of the bulk metal is approached as the number of atoms in the particles increases. The size effects in the optical functions of the metallic particles are shown to depend on the environment and this is made to account for the basic features in the optical properties, in particular for the resonance plasma absorption. The case of silver particles in a glassy environment is investigated, experimental trends of the optical absorption with varying particle sizes are explained and reasonable agreement with experimental data is obtained. Based on work supported in part by the Italian Research Council (C.N.R.) through a contract G.N.S.M. and by the French Ministry of National Education (Ministère de l'Education Nationale).     

Reflectance magnetocircular-dichroism spectra and electronic structures of CdCr2Se4

Summary Reflectance magnetocircular-dichroism spectra of a ferromagnetic semiconductor CdCr₂Se₄ were measured for temperatures between 4.2 K and 157 K. Off-diagonal elements of the dielectric tensor were calculated from the measured spectra. A number of fine structures was resolved, the energy position of which was plotted against temperature. It is found that there are two red-shifting structures: one at 1.1 eV (the well-known absorption edge) and the other at 1.9 eV. Other structures show slight blue-shift. These energy positions were compared with the band structure calculated by means of the self-consistentDV-Xα technique. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Single-photon interference experiment using a mechanical frequency shifter

Summary A variation of the interference experiment on the single photon has been performed. By means of a mechanical effect, we change the frequency of the photon only on one arm of a Mach-Zender interferometer. We observe the beat signals even when the intensity is so small that only one photon at a time passes through the interferometer. Our experiment gives a further proof of the classical behaviour of the electromagnetic radiation at arbitrarily small intensity, in agreement with the probabilistic interpretation of quantum mechanics.

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Riassunto è stata realizzata una variante dell'esperimento d'interferenza del singolo fotone. Variando, mediante un effetto meccanico, la frequenza del fotone soltanto in uno dei due bracci di un interferometro di Mach-Zender, si osservano segnali di battimento anche quando l'intensità è così bassa che solo un fotone per volta attraversa l'interferometro. Questo esperimento dà un'ulteriore dimostrazione del comportamento classico della radiazione elettromagnetica ad intensità arbitrariamente ppicole, in accordo con l'interpretazione probabilistica della meccanica quantistica.

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Резюме Осуществлен вариант интерференционного эксперимента с одним фотоном. С помощью механического эффекта мы изменяем частоту фотона в одном из плеч интерферометра Маха-Цендера. Мы наблюдаем сигналы биения даже в том случае, когда интенсивность настолько мала, что только один фотонодновременно проходит через интерферометр. Наш эксперимент указывает на классическое поведение электромагнитного излучения при произвольномалых интенсивностях, что согласуегся с вероятностной интерпретацией квантовой механики.

     

Normal-incidence exciton transmission and reflection spectra of semiconducting plane-parallel slabs

Summary Exciton transmission and reflection spectra of thin semiconducting crystals in the spectral region of excitonic polaritons are calculated by the Stahl's coherent wave approach. The influence of the crystal thickness and of the intrinsic damping is discussed. Calculations are performed for the lowest state of theA-exciton in CdS. Experimental results of Broseret al. (1985) are reproduced by inserting an appropriate energy-dependent damping. The research was supported by the Polish Ministry for Science and Higher Education, Program CPBP01.03.     

Light scattering from spin waves in superfluid3He-A

Summary We show that in theA-phase of superfluid³He one may expect the Mandelstam-Brillouin light scattering from spin waves. The scattering is caused by fluctuations of the magnetic susceptibility.

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Riassunto Si mostra che nella faseA del superfluido³He ci si può aspettare diffusione di luce di Mandelstam-Brillouin da onde di spin. La diffusione è caratterizzata da fluttuazioni della suscettibilità magnetica.

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Резюме Мы покаем, что ьА-qfазе сьерхтекучего³He μожно ожидать рассеяние света Мандельштама-Бриллюэна на спиновых волнах. Рассеяние обусповлено флуктациями магнитной восприимчивости.

     

Reflectivity and dynamical conductivity ofn-type HgCr2Se4

Summary Reflectivity measurements have been done on dopedn-type HgCr₂Se₄ (n≈(10¹⁵÷10¹⁹) cm⁻³), at various temperatures ((4÷300) K) in the infra-red range . The spectra show the structure of a plasma edge and reststrahlbands. Data have been analysed by a Kramers-Kronig procedure. The deduced dynamical conductivity shows an anomaly near the plasma frequency ω_p. The transmitivity measurements show a strong temperature dependence of the conduction band. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.