CdSe Single Crystals Research Articles

Luminescence from the Excited States of Excitons in CdS and CdSe Single Crystals

AbstractThe photoluminescence in “pure” crystals of CdS and CdSe atT  1.4, 4.2, and 77 °K and high exciton concentration has been investigated. The correlation between arising (having mainly threshold character) of luminescence from the excited states of excitons A(n  2, 3) and B(n  1) and the existence of a fine structure, related to radiative recombination due to inelastic collisions between excitons (P, P2, P3, P4, and PB−lines) is observed. It is shown that with increasing excitation the “blue” shift of P‐line is twice than that for the A(n  1)‐line. The analysis of the problem using kinetic equations leads to conclusions about the possibility of stimulated enlargement (similarly to laser generation) of exciton concentration in their excited states due to Auger‐throwing of the excitons into these states at luminescence of P‐lines. The numerical estimations correspond to the experimental condition and the agreeement to the theory with experiment permitsto conclude that the observable luminescence from the excited states is dueto the stimulated generation of excitons in these states.

Properties of dynamic and pulse holograms recorded in semiconducting materials

An experimental study was made of holograms recorded in semiconducting materials using clusters of free carriers in Si an CdSe single crystals, color centers in CaF2:La crystals, and structural changes in As2Se3 films.

Scattering centres and their relation to the recombination centres in single crystals of CdSe

Electrical and photoelectrical properties of undoped thermally annealed n- and p-type single crystals of CdSe have been studied. Two types of scattering centres are found: the first type (Ec – 0.75) eV is caused by cadmium vacancies, the second type (Ec – 0.6) eV by selenium vacancies. The strong dependence of carrier mobility on the population of these centres shows their multiple charges, possibly, double charges. The centres at (Ec – 0.75) eV also serve as fast recombination centres. Interstitial cadmium is either neutral or singly charged, but never doubly charged. Die elektrischen und photoelektrischen Eigenschaften nichtlegierter, thermisch behandelter n- und p-leitender CdSe-Einkristalle wurden untersucht. Es wurden zwei Typen Streuzentren festgestellt: der erste Typ (Ec – 0,75) eV wird durch Kadmiumleerstellen, der zweite (Ec – 0,6) eV durch Selenleerstellen hervorgerufen. Die Beweglichkeit hangt stark von der Besetzung dieser Zentren ab, was bedeutet, das diese Zentren mehrere, moglicherweise zwei Ladungen besitzen. Die Zentren bei (Ec – 0,75) eV wirken als schnelle Rekombinationszentren. Kadmium auf Zwischengitterplatzen ist stets neutral oder besitzt eine, aber nie zwei Ladungen.

1102. Photoluminescent properties and amplification coefficient of CdS and CdSe single crystals at electron-beam excitation

This paper provides a theoretical survey and further experimental data of kinetically controlled stationary dark and photocurrents on n-GaAs and n-GaP electrodes.The mechanism of anodic photodissolution is treated in greater detail, taking explicitly into account a sequence of kinetic steps. The possibility to detect partial charge transfer steps in stationary photocurrent-voltage curves is examined and related experimental data are discussed.Effects of photoinduced surface layer formation which takes place under certain conditions are briefly reported.

Transmission spectra of CdSe single crystals at photon energies between 3.6 and 5.8 eV

Transmission spectra of CdSe single crystals at photon energies between 3.6 and 5.8 eV

P-type conductivity in undoped CdSe single crystals

Undoped single crystals of cadmium selenide grown by the method of static suulimation in an atmosphere of selenium vapour possess a p-type conductivity. The type of conductivity has been determined by the polarity of the Hall effect. From the temperature dependence of the Hall effect deep acceptors (from 0.63 to 0.65 eV of density between 10 14 and 10 15 cm −3 have been found. These centres are assumed to be caused by cadmium vacancies or by their complexes.

Photoluminescence of CdSe Single Crystals

As-grown CdSe single crystals exhibited mainly the emissions associated with excitons, and the diffusion of Li caused the intensity of edge emission to be marked. The difference in the peak wavelengths of edge emission at 4.2 K between the as-grown crystal and CdSe: Li seemed to be due to the difference in the donor-acceptor separation in the two specimens. The emission intensities in the exciton region, especially the P-line, decreased after plastic bending. The relationship between the luminescence of deep centers and several impurities was studied and the 1.50 eV emission was ascertained to be related to Ag.

1556. Investigation of electrical conductivity of CdSe single crystals in the region of high temperatures: Yu V Rud and K V Sanin, Ukraine Fiz Zh, 18 (8), 1973, 1377–1383 ( Russian

Periodically poled lithium niobate is an important component in mid-infrared lasers due to its perfect nonlinear optical property. However, fabrication of high-power laser based on periodically poled lithium niobate is still a great challenge, because lithium niobate crystal wafer with large thickness for large clear aperture periodically poled lithium niobate is hard to be completely poled due to the high coercive field of commercial congruent lithium niobate (LiNbO3). In this work, we have successfully grown 3-inch near-stoichiometric LiNbO3 by efficiently regulation of temperature gradient with the aid of thermal field simulation. Characteristics on the as-grown large size near-stoichiometric LiNbO3 proved that the [Li]/[Nb] of crystal is around 1:1, and the crystal possesses a typical single domain with high optical homogeneity. Compared with congruent and Mg-doped LiNbO3, the near-stoichiometric LiNbO3 crystal has better piezoelectric performance. The forward and backward coercive fields of the near-stoichiometric LiNbO3 crystal were 2.90 kV/mm and 2.43 kV/mm, respectively, which were approximately 8 times lower than that for CLN (21 kV/mm). The periodically polarization experiments proved that only 1.36 kV can realize the complete polarization for a 1 mm thick near-stoichiometric LiNbO3 wafer. The mass-productive near-stoichiometric LiNbO3 crystals grown in this work will have great applications in high-power mid-infrared solid-state laser.

Photoluminescence and gain of CdS and CdSe single crystals under electron-beam excitation conditions

An investigation was made of the photoluminescence spectra of cadmium sulfide and selenide single crystals (77 and 4.2°K) and of the spectra of the gain α(ħω) during excitation of the same crystals with electron beams of 20 keV energy (77°K). The experimental and calculated gain profiles were compared on the assumption of the exciton–phonon interaction between carriers. A correlation was found between the photoluminescence and gain spectra. Gains up to 70 cm–7 were obtained for CdS crystals whose 77°K photoluminescence spectra included a strong (compared with the edge luminescence) band due to A free excitons, and there was clear evidence of transitions assisted by one or two longitudinal optical phonons. In the case of CdSe crystals grown by the sublimation of a powder in an argon stream the maximum gain and full agreement between the experimental and calculated gain profiles were obtained when these crystals were grown in the temperature range 800–900°C.

Granular metal-semiconductor Schottky barriers

Granular metal-semiconductor barriers were investigated on n-type Si, GaAs, and CdSe single crystals. The barriers were formed by cosputtering metals, Au or Ni, and insulators, SiO2 or Al2O3, onto the semiconductor surface. By varying the relative volume fraction of the insulator over the range 0–90%, the structure of the granular metal changed from that of a continuous metal to that of isolated small ([inverted lazy s]20 Å ) metallic particles embedded in the insulator. Even with as little as 10% by volume of the metal, the granular metal contacts were found to behave as metal-semiconductor Schottky barriers. In the composition range 60–90% insulator in the granular metal, the barrier heights were independent of composition and their values were 0.57, 0.58, and 0.65 eV on Si, GaAs, and CdSe, respectively. In the case of Si and GaAs, the barriers are significantly lower than those observed for the pure metals; in the case of CdSe no such difference is found.

Electron trapping levels in cadmium selenide single crystals

Measurements of space-charge-limited currents have been performed on CdSe single crystals between 77 and 400 °K. Four groups of electron trapping levels have been found at 0.64, 0.49, 0.35, and 0.167 eV, with densities ranging from 5 × 1010 to 1013 cm−3. A check of the results with photocurrent vs light intensity and thermally stimulated currents measurements is presented. The origin and the nature of these centers is discussed and correlated with mobility values measured in the crystals investigated. Finally, contacts and geometry considerations are reported.

The influence of mobility on photoconductivity in cdsesingle crystals at high excitation density

The influence of mobility on photoconductivity in cdsesingle crystals at high excitation density

CdSe single crystals with n- and p-type of conductivity approaching intrinsic

The properties of CdSe single crystals grown by static sublimation in an atmosphere of the excess selenium vapor both in the presence of argon and without it have been analyzed. The conditions for obtaining p- and n-type single crystals are given.

EPR Spectra of Transition Element Impurities with 3d2 Configuration in Hexagonal CdS and CdSe Single Crystals

AbstractElectron paramagnetic resonance has been studied for divalent titanium with 3d2 configuration substituting for Cd in hexagonal single crystals of cadmium sulphide and cadmium selenide. The parameters of the spin‐Hamiltonian have been determined at T = 27 and 77 K. It is found that the symmetry of the centre is axial, corresponding to the C3V symmetry of an isolated impurity on normal lattice sites in wurtzite.

Impact Ionization, Breakdown, and Photoinduced Switching in CdSe

Measurements of conductivity, Hall coefficient, and mobility of CdSe single crystals have been made in the temperature range 4.2-300 \ifmmode^\circ\else\textdegree\fi{}K. For the sample with the lowest carrier concentration of 2.8\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the donor ionization energy of 18 meV is obtained. This is in good agreement with the calculated hydrogenic value of 19 meV. Above 100 \ifmmode^\circ\else\textdegree\fi{}K, the electron---polar-optical-phonon interaction determines the mobility. Below 100 \ifmmode^\circ\else\textdegree\fi{}K, ionized- and neutral-impurity scattering also contribute to the mobility, and for $T<50$ \ifmmode^\circ\else\textdegree\fi{}K dominate the mobility. At relatively low fields, nonlinear $I\ensuremath{-}V$ characteristics are observed. The samples show breakdown around 100 V/cm (varies somewhat with carrier concentration), resulting in a region of current-controlled negative resistance. The conductivity, Hall coefficient, and mobility of the samples are measured in the high-field region. The samples which show current-controlled negative resistance can be switched from a low- to a high-conductivity state under illumination below the threshold field in the dark. The higher the intensity of illumination, the lower is the threshold field for switching. These results are discussed in terms of various models.

Study of the traps created in the single crystal of CdSe by the irradiation of Mo K α X-ray quantum

Traps were created in the single crystal of CdSe by bombardment with Mo Kα X-ray radiation. These traps were studied by the relaxation curves of photoconductivity, obtained at 6000 Å and after two dosages of radiation. It has been found out that the traps created were β-type.

Peculiarities in the growth of single crystal CdSe films on sapphire, fluorite and mica: A V Vanyukov and N M Kondaurov, Neorg Mater, 7 (11), 1971, 1956–1959 ( in Russian)

Peculiarities in the growth of single crystal CdSe films on sapphire, fluorite and mica: A V Vanyukov and N M Kondaurov, Neorg Mater, 7 (11), 1971, 1956–1959 ( in Russian)

Optical phonon drag effect in single crystals of CdSe

AbstractAn investigation is made of the optical phonon drag effect. In contrast to [1] where all calculations were performed for low carrier densities and the change of sign of phonon drag effect at low temperatures was obtained, it is shown in this paper that for high carrier densities no change of sign takes place. The phonon drag effect is found to be inversely proportional to the carrier density. These conclusions were checked experimentally on CdSe single crystals.

The influence of an electric field on the B, n = 1 ground state exciton line of CdS and CdSe single crystals

AbstractThe influence of an electric field has been measured for the B. n = 1 exciton line of CdS and CdSe single crystals. The results indicate a quadratic Stark shift in agreement with second‐order perturbation theory and a quadratic field dependence of half‐width.

Determination of exciton diffusion length from photoconductivity low‐temperature spectra

AbstractThe spectral distribution of the photoconductivity of CdS and CdSe single crystals has been investigated at 77 °K in a wide spectral range. The values of the exciton diffusion lengths in these compounds have been obtained from the photocurrent spectra using the absorption coefficient data. The exciton diffusion lengths were found to be within the range of 2000 to 10000 Å for CdS and 2000 to 4000 Å for CdSe. The proposed model involves the diffusion of the excitons to the surface, where they dissociate into free carriers interacting with the near‐to‐surface centres. The role of the space charge layer in these phenomena is discussed.