Fluctuations of current, electroluminescence and acoustic emission in light-emitting А³В⁵ heterostructures

It is shown, that in heterostructures based on A³B⁵ compounds acoustic emission occurrence, current and light fluctuations, evolution electroluminescence spectrums, current-voltage characteristics degradation occur simultaneously and has the common origin

Thermofield Cr→Cr²⁺ recharging resulting in anomalous intensification of Cr²⁺ emission in ZnS:Cr thin-film electroluminescent structures

For the first time, an anomalous strong increase of the Cr²⁺ emission intensity (I) with increasing the applied voltage (V) has been discovered in ZnS:Cr thin-film electroluminescent structures (TFELS) instead of the I(V) dependence saturation typical of TFELS of the MISIM type, where M is an electrode, I is an insulator layer and S is an EL film. The dependence of I on the transferred charge (Q) is very superlinear, whereas the luminance of the emission of hot electrons, which takes place simultaneously with the Cr²⁺ emission, increases proportionally to Q as it happens usually in TFELS. The increase of I and Q is accompanied by rising the sample temperature up to 30 – 50 °C. However, the emission spectrum that is inherent to the ⁵E → ⁵T₂ transition in the 3d shell of a Cr²⁺ ion is not changed in this case. The above effects are explained by Cr⁺ → Cr²⁺ thermofield recharging, which results in an increase of the number not only of free electrons, but also of Cr²⁺ radiation centers. The most probable mechanism of such a recharging is the Frenkel-Pool field-stimulated thermal ionization of Cr⁺ ions, whose ionization energy is 0.65…0.82 eV

Stimulated emission of Cr²⁺ ions in ZnS:Cr thin-film electroluminescent structures

First observation of stimulated Cr²⁺ emission in ZnS:Cr electroluminescent (EL) impact-excited thin-film waveguide structures is reported. The structures consist of the following thin films deposited on a glass substrate: a transparent In₂O₃:Sn electrode, an insulator SiO₂/Al₂O₃ layer (~270 nm), an EL ZnS:Cr film (~600 nm), the same insulator layer, and an Al electrode. The stimulated character of the emission recorded through the edge of the structure is evidenced by the following. With increasing the applied voltage, a broad band with three waveguide mode maxima in the edge emission spectrum changes into an intensifying and narrowing band. The maximum of this band is the same as that of the Cr²⁺ emission band recorded through the face, i.e. through the In₂O₃:Sn electrode (1.75 and ~2.6 µm at the Cr concentrations (5-7)*10¹⁹ and (2- 3)*10²⁰ cm⁻³, respectively). The five-fold narrowing is observed when increasing the voltage by ~4% in the case of the lower Cr concentration. The voltage and frequency dependences of the edge emission are stronger than those for the face emission. A small manifestation of the gain occurrence in the ZnS:Cr TFELS is also observed in the face emission. The possibility to create a new type of electrically pumped lasers with the impact excitation mechanism is discussed

Mid-IR impurity absorption in As₂S₃ chalcogenide glasses doped with transition metals

Room temperature IR impurity absorption spectra in 1 4000 7000 cm ( 4.1 - 25um ) region for chalcogenide glasses of As₂S₃ doped with chromium (0.5, 1 wt.%) and manganese (0.1, 1, 2, 5 wt.%) have been studied. The effects of chromium and manganese impurities on the transmission spectra are discussed

Laser oscillation in Cr²⁺:ZnS waveguide thin-film structures under electrical pumping with impact excitation mechanism

The laser oscillation at room temperature in Cr²⁺:ZnS waveguide thin-film structures under electrical pumping with the impact excitation mechanism was first discovered after improvement of some waveguide optical properties. However, lasing turned out to be unstable and ceases soon, which is accompanied by strong weakening the emission recorded from the waveguide edge whereas the emission from the structure face remains intensive. It is shown that the above changes stem from increasing optical losses caused by appearance of light scattering in the structure by inhomogeneities formed during lasing as a consequence the most probably of recrystallization processes in the Cr:ZnS film. Some ways are proposed to improve the lasing stabilit

Method for determination of the absorption coefficient in films based on photoluminophore suspension for white LEDs

Developed in this work is the method for measuring the absorption coefficient in optically non-homogeneous media (films prepared from photoluminophore suspension). Using this new method, the authors have measured the absorption spectrum of the above films with inorganic photoluminophore FLY-7. At the film absorption peak (near 448 nm) and photoluminophore concentration close to 20%, the absorption coefficient reaches 124 cm⁻¹ . Ascertained have been the conditions that should be provided when using this metho

Determination of the spectral dependence for the absorption coefficient of phosphor inorganic microparticles

Developed in the work has been the mathematical model of the composite film, which enables to calculate the wavelength dependence of the absorption coefficient of microcrystals in the phosphor composition. Also, developed has been a new method for determining the spectrum of the absorption coefficient for microparticles of powderlike materials. Being based on this method, obtained has been the wavelength dependence for the absorption coefficient of microparticles of inorganic phosphor ФЛЖ-7-01. At the emission peak of a blue LED (456 nm) their absorption coefficient is close to 684 cm⁻¹

Fourier Raman spectroscopy studies of the As₄₀S₆₀-xSex glasses

The present paper is concerned with the investigations of As₄₀S₆₀-xSex glasses with the help of Fourier Raman spectroscopy. The results of Raman spectroscopy investigations indicate increased presence of non-stoichiometric Sen, As₄S₄ fragments for intermediate compositions of As₄₀S₆₀-xSex glasses, which in combination with composition dependencies of molar volume, previous results on investigations of optical and thermal properties of As₄₀S₆₀-xSex can be explained by the small deviation from the statistical one under the isovalent substitution of Se on S in As₄₀S₆₀-xSex glasses with the composition change

Optical properties of quantum-sized structures and two-dimensional photon crystals fabricated in semiconductor substrates using irreversible giant modification

It is known that using the irreversible giant modification, it is possible to change locally the refractive index of semiconductors. This work is concerned with the development of the methods of photonic crystal formation basing on CdS, CdTe and GaAs semiconductors. It was shown that complex refractive index of the CdS, CdTe and GaAs semiconductor samples is changed significantly after their modification. For example, the complex refractive index of CdS is changed from 2. 75 + i2.8113 up to 1.9 + i0.035. The real and imaginary parts of CdS refractive index are decreased by 0.85 and 2. 7763, respectively, while the absorption coefficient is decreased by 80 times. It is also shown that the interface between modified and non-modified sample areas is submerged into the sample depth (the distance from the surface being at least 11 μm). Thus, one- and two dimensional photonic crystals for visible and ultraviolet ranges can be effectively obtained using CdS, CdTe and GaAs semiconductor substrates by modifying thereof without complex lithographic technology.Відомо, що за допомогою незворотної гігантської модифікації можна локально змінювати коефіцієнт заломлення напівпровідників. Ця робота присвячена розробці методики формування структур фотонних кристалів у напівпровідникових матеріалах CdS, CdTe і GaAs. Показано, що комплексний показник заломлення у напівпровідниках CdS, CdTe і GaAs значно змінюється після вищезгаданої модифікації. Для CdS комплексний коефіцієнт заломлення змінюється від величини 2,75 + i2,8113 до 1,9 + i0,035. Дійсна та уявна частини комплексного коефіцієнта заломлення у CdS зменшуються відповідно на 0,85 і 2,7763, а коефіцієнт поглинання зменшується у 80 разів. Також показано, що границя розділу між модифікованими та немодифікованими ділянками знаходиться під поверхнею зразка, на глибині щонайменше 11 мкм. Із застосуванням такого способу модифікації оптичних властивостей напівпровідників можна виготовляти одно- та двовимірні фотонно-кристалічні структури для видимого і ультрафіолетового діапазонів на напівпровідникових субстратах зі сполук CdS, CdTe і GaAs без використання складних багатоступінчастих літографічних технологій.Известно, что с помощью необратимой гигантской модификации можно локально изменять коэффициент преломления полупроводников. Настоящая работа посвящена разработке методики формирования структур фотонных кристаллов в полупроводниковых материалах CdS, CdTe и GaAs. В работе показано, что комплексный показатель преломления в полупроводниках составов CdS, СdТе и GaAs претерпевает значительные изменения после вышеупомянутой модификации. Для CdS комплексный коэффициент преломления изменяется от величины 2,75 + i2,8113 до 1,9 + i0,035. Действительная и мнимая части комплексного коэффициента преломления CdS уменьшаются на 0,85 и 2,7763 соответственно, а коэффициент поглощения уменьшается в 80 раз. Также показано, что граница раздела между модифицированным и не модифицированным участками находится под поверхностью образца, на глубине не менее 11 мкм. С применением такого способа модификации оптических свойств полупроводников можно изготавливать одно- и двумерные фотонно-кристаллические структуры для видимого и ультрафиолетового диапазонов на полупроводниковых подложках составов CdS, CdTe и GaAs без использования сложных многоступенчатых литографических технологий