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The high-quality ZnO single crystals were grown by seeded chemical vapor transport (CVT) in a newly designed ampoule using carbon as a transport agent. The well-faceted crystal of about 5×5×5 mm 3 can be grown reproducibly. Secondary ion mass spectroscopy (SIMS) analysis, X-ray rocking curve (XRC) and photoluminescence (PL) measurements demonstrate that the grown single crystal is of high purity and high crystallinity.

Zinc oxide (ZnO) single crystal was grown, for the first time, by the self-flux method using a high-purity zinc solvent saturated with oxygen. ZnO crystals were successfully grown in the solvent by moving a growing crystal slowly, at about 17 mm/day along a temperature gradient (1.5 °C/mm) in a furnace, from 1050 to 500 °C. Hexagonal single crystals 1–3 mm in length and 0.5–1 mm in thickness were obtained. Energy-dispersive X-ray diffraction, secondary ion mass spectrometry, and photoluminescence confirmed that the purity and crystallinity of the ZnO crystals grown in this work were high.

We have successfully grown high-purity and -quality PbI 2 single crystals by the vertical Bridgman method. The rocking curves of four-crystal X-ray diffraction (XRD) show 120 arcsec in full-width at half-maximum (FWHM). The photoluminescence (PL) spectra at 7.8 K show the resolved intensive exciton emission line and the weak DAP emission band. The deep-level emissions are not observed. The measurement of the electrical and radiographic properties show that Leadiodide (PbI 2 ) single crystal has a resistivity of 5×10 10 Ω cm and imager lag is 8 s, respectively. In order to improve the controllability of crystal growth, PbI 2 single crystals were also grown from a lead (Pb) excess PbI 2 source. The experimental results show very good reproducibility. In addition, the growth models of crystal are proposed, and the growth mechanism is discussed.

β-Iron disilicide (FeSi 2 ) single crystals were grown by the chemical vapor transport (CVT) with iodine (I 2 ) as a transport agent. The optical and electrical properties of the crystals were then studied. Raman spectrum shows a set of strong A g -mode peaks and photoluminescence (PL) spectra show a very broad emission band. In order to study the effect of annealing on the electrical properties, β-FeSi 2 single crystals were annealed in the range of 1073–1213 K for 48 h. The electrical properties of as-grown and annealed crystals were then evaluated by measuring their Hall effects in the temperature range of 10–300 K. The results show that both of the as-grown and annealed single crystals are of the n-type conductivity. The dependences of the temperature indicate that carrier concentration decreases and Hall mobility increases with the increase of measuring temperature. When the annealing temperature reaches above 1223 K, these changes tend to saturation. Furthermore, the donor ionization energies were estimated and the scattering mechanisms of carrier were discussed.

ZnO crystal growth by chemical vapor transport (CVT) is carried out using CO 2 and Zn as a new transport agent. ZnO crystals are grown by the reaction: ZnO ( s ) + CO ( g ) = Zn ( g ) + CO 2 ( g ) . The increase in CO 2 / Zn changes the color of as-grown crystals from red to transparent. The color change of the crystals is due to the oxygen partial pressure during the CVT. The red color of crystals is attributed to defects caused by the shift of stoichiometry to zinc-rich (oxygen vacancies, zinc interstitials, or their complexes are created). All of the grown crystals are polycrystals by using the ordinary CVT ampoules. Single crystals are grown reproducibly by using a seed and a CVT ampoule with modified configuration.

Nitrogen (N) doped ZnSe homoepitaxial films and bulk single crystals doped with phosphorus (P), antimony (Sb) and bismuth (Bi), have been grown by metal–organic chemical vapor deposition (MOCVD) and Bridgman method, respectively. By examining photoluminescence (PL) spectra at low temperature, it is found that group Va elements act as both shallow acceptor and deep donor. To enhance the net acceptor concentration, ZnSe:Va specimens are annealed at different temperatures. The experimental results show that doped Va elements except P are activated remarkably. The C–V measurements show that the highest net acceptor concentration is 6.7×1017 cm−3 in ZnSe:N. Furthermore, the ionization energies of Va elements as acceptors and deep donor complexes are estimated.

The chemical vapor transport (CVT) with iodine as a transport agent used to grow the β-iron disilicide (FeSi 2 ) single crystals in the present study. To examine the growth conditions, the source temperature is fixed at 1323 K, and the temperatures of the crystallization zone are changed from 923 to 1223 K. The results show that Si, e-FeSi, β-FeSi 2 and α-FeSi 2 phases are formed in the ranges of 923–1108, 950–1193, 1108–1173 and 1173–1223 K, respectively. Fe phase is not found in the crystallization zone in all runs. This shows that the growth process is controlled by Fe transport rate. Using determined growth conditions, β-FeSi 2 single crystal with a dimension of 22.0×3.5×1.0 mm has been obtained. To our knowledge, this is the largest volume β-FeSi 2 crystal till now.

The crystal growth process of zinc oxide (ZnO) by chemical vapor transport (CVT) using carbon as the transport agent is developed. The comparison between the chemical reaction rate and the diffusion velocity is our primary point of view. In ordinary CVT systems, the transport rate is diffusion-limited because the chemical reactions of both source and growth sides reach an equilibrium extremely faster than the diffusion velocity. Nevertheless, in our system, the transport rate is kinetics-limited because the estimated chemical reaction rates are slower than the diffusion velocity. Configurations of ampoules have been devised to decrease the diffusion velocity and to change from the kinetics-limited transport to the diffusion-limited one. Then the reproducibility of ZnO single crystal growth was considerably improved.

β -FeSi 2 single crystal epitaxial films were successfully grown on hydrogen terminated Si (1 1 1) substrates by using solid source molecular beam epitaxy (SS-MBE). The β -FeSi 2 epitaxial film with thickness of 180 nm was grown without template-layer or post-growth annealing. By analyzing X-ray diffraction (XRD) patterns and the corresponding scanning electron microscopy (SEM) images, the optimal growth temperature was established to be 580 °C. To study the effect of Fe/Si ratio on the film quality, a series of epilayers were grown at 580 °C with various Fe/Si ratios from 2 to 0.4. The stoichiometric Fe/Si flux ratio of 0.5 was confirmed to be an essential condition to grow single crystalline β -FeSi 2 epitaxial films at 580 °C, while the metallic e -FeSi phase grew predominantly at 480 °C. The observations of transmission electron microscope (TEM) and reflective high-energy electron diffraction (RHEED) verified the epitaxial growth of β -FeSi 2 films on Si (1 1 1).

ZnO crystal growth by chemical vapor transport (CVT) is carried out using carbon as a transport agent. Under the optimum Δ T and growth temperature, a single crystal was grown. The carbon contamination is not detected by SIMS measurements and all the crystals are orange-red colored. It is claimed that the orange-red color is attributed to the shift of stoichiometry to zinc rich atmosphere.

The dominant luminescence emission of excitons bound to a neutral acceptor defect (A0, X) in as-grown high purity CdTe single crystals has been studied by Cd-dip treatment, doping with Cu and Ag, and irradiation with γ-rays from 60Co. It has been demonstrated that, by Cd-dip treatment, the dominant (A0, X) emission can be annihilated to be a double-structure emission with their energy at 1.5896 and 1.5885 eV, respectively. Our doping experiments have unambiguously shown that (A0, X) at 1.5896 eV is associated with residual impurities of Cu and (A0, X) at 1.5885 eV with Ag. Further experiment with γ-ray irradiation has revealed a new (A0, X) emission at 1.5892 eV in the double structure. We suggest that this emission is associated with Cd-vacancies introduced by γ-rays. To our knowledge, this is the first report on the isolated Cd-vacancies showing (A0, X) emission with the energy position different from 1.5896 eV.

Cadmium telluride (1 1 1) epitaxial layers were directly grown by hot wall epitaxy (HWE) on the hydrogen-terminated Si(1 1 1) substrate without any preheating treatment. Low-temperature photoluminescence and four-crystal rocking curves X-ray diffraction (XRD) were used to establish the optimum growth conditions for HWE of CdTe/Si(1 1 1). Two-step growth regime was originally designed for obtaining high-quality CdTe crystal epilayers for further fabrication of Hg1−xCdxTe infrared detectors. Four-crystal rocking curves XRD data indicate significantly improvement in the crystal quality after applying the two-step growth regime, and the best full-width at half-maximum value of 118 arcsec was obtained for 5 μm thick epilayer.

The Effects of Cd-atmosphere annealing and Cd-dip treatment on high purity CdTe single crystals have been studied thoroughly. It has been presented that the Cd-dip treatment could change the dominant (A 0 , X) peak in PL spectrum for as-grown crystal into (D 0 , X) for Cd-dipped crystal. This result shows that the conductivity of specimen has been converted from p-type into n-type. By measuring the reflective spectrum of the Cd-dipped specimen, very clear free-exciton (FE) emission peak has been detected. This observation of FE emission indicates that the CdTe single crystal is of very high purity.

Using a perfect single crystal sample of CdTe grown using PVT method, the electronic charge transfer in the II–VI compound semiconductor CdTe at 200 and 300 K has been evaluated using two different approaches: (1) by solving a quadratic equation involving the observed structure factors of h + k + l =4 n +2 type reflections; and (2) by a graphical approach in which the observed and calculated atomic form factors are extrapolated to sin θ/λ=0 , to determine the transferred charge. Precise X-ray structure factors collected using MoK α radiation have been used for the analysis. The results obtained are reasonable and clearly indicate the ionicity by which charge is transferred from Cd to Te in CdTe.

Compensating defects were studied in high purity Al-doped CdTe single crystals using its photoluminescence at 4.2 K and its temperature dependence. The acceptor complex defect (V Cd -Al Cd ) is found to give bound exciton emission at 1.5848 eV, and its related DAP emission at 1.453 eV. Furthermore, the bound exciton emission and DAP emission associated with the another complex defect (V Cd -2Al Cd ) is found at 1.5906 and 1.553 eV, respectively.

Extremely high-purity CdTe single crystals have been obtained by the traditional vertical Bridgman technique, beginning with the refining of tellurium material by the normal freezing method. The purification effect of normal freezing on tellurium has been confirmed to be very effective. This effect was also used to prepare extremely high-purity CdTe single crystals. The crystals were characterized by low temperature high-resolution photoluminescence (PL) spectroscopy. Only a sharp peak at 1.5896 eV was detected in the PL spectrum. The full-width at half-maximum is

High quality ZnTe epilayers on (1 0 0) GaAs substrates have been successfully grown by hot wall epitaxy. The strain in the hetero-interface has been studied by four-crystal X-ray diffraction and transmission electron microscopy (TEM). The smallest FWHM value of the four-crystal X-ray rocking curve was 66 arcsec, which is the best so far value reported. On the other hand, the reciprocal lattice mapping indicates a splitting of the (4 0 0) peaks from the GaAs substrate, indicating the existence of a strained region in the substrate. A TEM study confirms that the strain exists not only in the ZnTe epilayers but also in the GaAs substrate near the interface. This is the first such direct observation for the case of ZnTe/GaAs.

A closed, double-crucible has been proved to be very successful for preventing the deviation from the stoichiometric compositions of the melt in the process of ZnSe Bridgman growth, and to be necessary for preparing large twin-free ZnSe single crystals. Under the optimized growth conditions, ZnSe crystals have been grown from the source materials with different composition ratio (Zn/Se) of 1.03-0.98. Photoluminescence spectra show that the I d 1 , I 2 and I 1 emissions are dominant for sample is with Zn/Se= 1, Zn/Se > 1, and Zn/Se 1 is low-resistivity, n-type, and Zn/ Se < 1 is low-resistivity p-type. The highest carrier concentrations of n- and p-type ZnSe crystals are 8.8 x 10 17 cm -3 and 1.8 × 10 17 cm 3 , respectively. These results show that low resistivity n- and p-type ZnSe single crystals can be successfully grown by changing the compositions of the starting materials.

It has been proved that the net acceptor concentration as high as 2 × 10 17 cm - 3 Can be obtained when ZnSe:N homoepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) are annealed in molten zinc. However, it was found that the emission intensity of two sets of donor-acceptor pair (DAP), shallow DAP (D s AP) and deep DAP (D d AP), increased with the increase in annealing temperature. In order to clarify the compensation effect, the study on the origin and the concentration of deep donor related to the D d AP emission should be carried out. The ionization energies of acceptor and deep donor were estimated to be 101 ± 1 and 44 ± 5 meV, respectively, by examining the dependence of their emission peaks with the excitation intensity. Furthermore, the upper limit of the deep donor concentration was estimated to be 1 × 10 16 cm -3 . This is one magnitude smaller than the net acceptor concentration obtained from the annealed ZnSe: N homoepitaxial layer in our previous paper. By studying on the behaviors of deep donor, the main reason to lead to a low net acceptor concentration in the ZnSe:N epitaxial layers is not attributed to deep donor complex containing nitrogen atoms, but hydrogen passivation, although a part of doped-nitrogen atoms combine with other defects to form complicated defects.

Owing to the different vapor pressures of zinc and selenium, the deviation from the stoichiometric compositions of the melt occurs during melt growth. In order to overcome this problem, we have adopted a closed double-crucible assembly consisting of an inner pBN crucible and an outer molybdenum capsule. To decrease the density of twins, an optimum temperature gradient at the growth interface of 30 K/cm and a growth rate of 3.6 mm/h have been determined. Using these growth conditions, we have grown successfully twin-free high-quality ZnSe single crystals with an EPD of 2.0×10 5 cm −2 and an FWHM of 19 arcsec by the vertical Bridgman technique.

The ZnSe : N epitaxial layers were grown on (1 1 0) ZnSe substrates in a low-pressure metalorganic chemical vapor deposition (MOCVD) system using hydrogen as a carrier gas, and using ammonia as a dopant source. In order to obtain highly doped ZnSe : N epitaxial layers, the optimum growth and doping conditions were determined by studying the photoluminescence (PL) spectra from the ZnSe epitaxial layers grown at different ammonia flux and VI/II flux ratio. Furthermore, in order to enhance the concentration of active nitrogen in ZnSe epitaxial layer, a rapid thermal anneal technique was used for post-heat-treating. The results show that the annealing temperature of over 1023 K is necessary. Beside, a novel treatment method to obtain a smooth substrate surface for growing high quality ZnSe epitaxial layers is also described.

(1 0 0)CdTe epitaxial films were grown on semi-insulating (1 0 0)GaAs substrates in order to determine optimum growth conditions by the hot wall epitaxy (HWE) technique. Further, CdTe epitaxial films with thicknesses of 0.84–14.9 μm were grown under determined optimum growth conditions for studying the effect of the thickness on crystalline quality. The low-temperature photoluminescence (PL) and X-ray diffraction (XRD) were used to evaluate the grown films. The results indicate that the density of extended defects in CdTe films decreases rapidly within 5 μm with the increase of thickness, and that high-quality CdTe epitaxial films on GaAs can be obtained at a thickness of over 10 μm. Several emission origins in PL are also discussed.

Single crystal films of ZnSe have been grown on nonpolar GaAs(1 1 0) surfaces by molecular beam epitaxy (MBE). The epitaxial films have been characterized by in situ reflection high-energy electron diffraction (RHEED), ex situ scanning electron microscopy (SEM) and X-ray diffraction. RHEED and SEM images of the surfaces reveal the formation of facets which are aligned along the [0 0 1] direction. The formation of facets indicates that ZnSe growth on the (1 1 0) surface proceeds 6°–13° off the vicinal (1 1 0) surface. Facet-free ZnSe surface has been successfully grown on a GaAs(1 1 0) 6°-off the substrate.

We have examined the aging behavior of some residual impurities in CdTe single crystals grown by vertical Bridgman method. The emission intensities of neutral donor bound exciton (D 0 , X) and neutral acceptor bound exciton (A 0 , X) related to Ag, P, Li and Na are found to obviously decrease with the aging time. This behavior, in the cases of Ag, Li and Na, is attributed to the instability of these elements occupying Cd sites. However, the decrease of (D 0 , X) and (A 0 , X) related to P suggests more complicated interaction among impurities and native defects and the formation of various complexes. These observations and their interpretation were confirmed by Ag-doping experiments.

High purity CdTe single crystals have been grown by improved physical vapor transport (PVT), following the purification by normal freezing using 6N Te and highly purified Cd as starting materials. As-grown single crystals were characterized with photoluminescence and photo-excited cyclotron resonance (CR) at 4.2 K and infrared transmission at room temperature. The improved PVT growth ampoule was confirmed very effective for controlling the growth rate and the reproducibility of a successful growth. Electron cyclotron mobility at 4.2 K is as high as 2.5 × 10 5 cm 2 /V · s and the neutral donor concentration ( N D ) obtained from the linewidth of CR is 5 × 10 14 cm −3 .

CdTe single crystals were grown by vertical Bridgman (VB) and physical vapor transport (PVT) methods. The photoluminescence was measured at 4.2 K to evaluate the crystals and to examine the behavior of residual impurities and the effect of Cd purity. The segregation of dominant residual impurities was confirmed in VB as-grown crystals. The purification effect of PVT was also confirmed. The dominant emission line (A 0 ,X) at 1.5896 eV in the PL spectrum, related to Cu Cd or V Cd , has been found to have a doublet structure shared by two origins, though a complete understanding is still lacking.

The feasibility of a far-field single-slit laser diffraction technique for in-situ growth rate measurements in physical vapour transport was demonstrated with CdTe single crystals. With a special crystal growth ampoule and a furnace with high optical quality windows, a resolution of better than 1 μm was achieved. It was found that the growth rate of CdTe decreases significantly with growth time. In addition, the dependence of the growth rate on supersaturation ( ΔT ) was investigated.

Lithium was incorporated into high purity ZnSe single crystals by dipping the crystal into molten Se-0.1 at% Li alloy at 673 K. The ILi1 line and two types of donor-acceptor pair (DAP) emissions (Q and R series) are observed. The acceptor binding energy of 105 meV is obtained for LiZn from the results of the excitation intensity dependence of the peak energy of DAP emissions. Comparison with the previous results of Na-doped crystals reveals that the R series is attributed to Lii−LiZn pairs and the Q series both to GaZn−LiZn and to Nai−NaZn pairs. The donor binding energies for Lii and Nai are estimated to be 15 ± 1 and 16 ± 1 meV, respectively.

Hetero-epitaxial growth of Pb 1− x Cd x S 1− y Se y on the substrates of (111) BaF 2 , (111)CaF 2 and (100)PbS was studied by the hot-wall method. Efforts were made to control the compositions ( x , y ) and conductivity type of the films by changing the growth parameters such as the temperatures of substrate, source and sulfur reservoir. Experiments were performed from binary PbS to quaternary Pb 1− x Cd x S 1− y Se y and consequently Pb 0.965 Cd 0.035 S 0.915 Se 0.085 films with the desired band-ga p and conductivity type were grown on a lattice-matched PbS substrate. This proved a possibility of multilayer growth with a double hetero-structure by the hot-wall method usage in lasers.

ZnSe 1− x Te x thin films have been grown on (100)GaAs and (100)InP substrates using an atmospheric pressure MOCVD. In the whole range of x , ZnSe 1− x Te x epitaxial films are grown on both substrates at 523–673 K using DEZn, DESe and DETe as the sources. It is found that the value of x in the grown films can be controlled by changing the ratio of supplies of DESe and DETe, though the value of x is higher than the fraction of DETe in the VI sources. The growth rate depends on the value of x .

High purity zinc selenide single crystals have been grown by a vapor phase transport method, using a commercial grade high purity selenium and the zinc purified by vacuum distillation and overlap zone-melting. Photoluminescence spectra measured on the grown crystals are confirmed to be affected considerably by the purity of zinc used and show that the crystals are of good quality. After the Zn-dip treatment, the Id1 line disappears, the peak energy of Ex decreases from 2.8024 to 2.8019 eV, and the emission intensities of Ex-LO and Ex-2LO become strong. The notable spectral feature observed on the purest crystal is that the emission intensities of the I3 lines become stronger than those of the I2 lines. For some of the crystals, a new emission band is found at 2.8002 eV and its intensity is found to be non-linearly dependent upon the excitation intensity.

We have prepared high purity ZnSe single crystals with donor concentrations less than 10 15 /cm 3 and characterized the doped and undoped ZnSe single crystals using photoluminescence and cyclotron resonance techniques. Photoluminescence and photoluminescence excitation spectra on the purest crystal reveal (1) that a Zn-dip treatment increases the free exciton life time, (2) that the free excitons recombine on the lower excitonic polariton branch, (3) that the intensities of I 3 become larger than those of I 2 , and (4) that each I 3 line has excited states, which are rather more complicated than those of the I 2 lines. We have observed for the first time cyclotron resonance absorption of photoexcited electrons and holes. This means that the grown crystals are not only of high purity but also of high quality. Isotropic effective masses ( m ∗ e = 0.145 m 0 and m ∗ h = 1.04 m 0 ) and cyclotron mobilities at 4.2 K (μ e = 470,000 cm 2 /V·s and μ h = 210,000 cm 2 /V·s) have been obtained. Doping experiments with In and Cu reveal that the difficulties of preparing low resistivity p-type crystals, such as self-compensation and the amphoteric behavior of dopants, can be solved by heat treatments after doping.

High purity zinc selenide single crystals have been grown using commercial high purity selenium and zinc purified by vacuum distillation and overlap zone-melting. The photoluminescence spectra measured at 4.2 K on the grown crystals are confirmed to be affected considerably by the purity of the zinc used. In the case of the purest crystal, the emission intensity related to donor bound excitons is remarkably small compared to that due to the recombination of free excitons. Moreover, no emission band is observed in the phonon energy below 2.4 eV.

Segregation coefficients of Ag, Co, I and In have been determined by means of a new method using radioactive tracers. Radioisotopes are incorporated, without any contamination, by producing them in the CdTe specimens through the nuclear reactions, (p, n) and (γ, p). 56 Co is implanted into the specimens using the recoil energy of the reaction 56 Fe(p, n) 56 Co. Segregation coefficients are estimated using normal freezing theory from distributions of each of the radioactivities in the single crystals grown by the Bridgman method. The obtained values of the segregation coefficients on Ag, Co, I and In are 0.2, 0.3, 0.22 and 0.43, respectively.