Growth Of ZnS Research Articles

MOVPE growth of ZnS xSe 1− x/GaAs(1 0 0) using ditertiarybutylselenium, tertiarybutylmercaptan and dimethylzinc triethylamine as precursors

Metal-organic vapor-phase epitaxy (MOVPE) at atmospheric pressure has been used to grow ZnS x Se 1− x epitaxial layers on (1 0 0)GaAs substrates. Ditertiarybutylselenium (DTBSe), tertiarybutylmercaptan (t-BuSH) and dimethylzinc triethylamine (DMZn : Et3N) were used as the selenium, sulfur, and zinc sources, respectively. The dependence of the composition of the ZnS x Se 1− x films on the partial pressures ratios R VI = p S/( p S + p Se) and R IV/II = ( p S + p Se)/ p Zn was investigated. The conditions for growing ZnS x Se 1− x alloy with x = 0.07 (lattice matched on GaAs) were therefore determined. In addition, the growth of ZnS x Se 1− x /ZnSe quantum wells was investigated. The structural characterization data show a strong dependence on the growth conditions. Excellent layer quality with sharp PL peaks and low values of the X-ray rocking curve width for x around 0.07 was obtained. A very intense and sharp (FWHM = 2 meV) PL emission was obtained for a ZnS 0.08Se 0.92/ZnSe quantum well with a 10 nm thick well.

MBE growth and characterization of ZnS 1− xTe x and Zn 1− yMg yS 1− xTe x alloys

ZnS 1− x Te x and Zn 1− y Mg y S 1− x Te x epilayers were grown on (1 0 0)GaAs by MBE. Ternary and quaternary alloys can be lattice matched to GaAs by adjusting the composition of the group VI and group II elements. Zincblende structure layers were grown and p-doping was achieved. A fairly good ohmic contact profile was obtained between gold and the alloy. By using the Au/p-ZnS 1− x Te x contacting layer, ohmic contact was obtained to p-ZnSe. p-Zn 1− y Mg y S 1− x Te x layers were applied to cladding layers of the LED, and bright luminescence was observed.

ZnSe/ZnS Distributed Bragg Reflectors in the Blue Region Grown on (311)B GaAs Substrates

High-reflectivity distributed Bragg reflectors (DBRs) in the blue region consisting of II–VI semiconductors were grown on (311)B GaAs substrates for the first time using metalorganic vapor phase epitaxy. ZnSe/ZnS alternative layers were used as the DBR. To realize atomically flat surfaces, the conditions of the thermal cleaning and the growth of ZnSe and ZnS on (311)B GaAs surfaces were investigated using atomic force microscopy and X-ray diffraction. The supply of sufficient organic As flow during the thermal cleaning led to extremely-flat (311)B GaAs surfaces, and it was attributed to the suppression of As desorption from (311)B surfaces. Through the examination of the growth conditions for ZnSe and ZnS layers on (311)B GaAs substrates, a DBR with a high reflectivity was fabricated. The maximum reflectivity of the ZnSe/ZnS DBR grown on the (311)B GaAs substrate, measured at room temperature, was 94.5% with only 10 periods at a wavelength of 468 nm, which is in good agreement with the calculated reflectivity of 94.8%.

AFM studies on ZnS thin films grown by atomic layer epitaxy

Polycrystalline ZnS films were grown from ZnCl 2 and H 2S on glass and mica using the atomic layer epitaxy (ALE) technique. Morphological and crystalline changes during the ALE growth of ZnS were studied by AFM and XRD. AFM measurements revealed that substantial agglomeration took place in the beginning of the growth. On glass the nucleation density of ZnS was higher than on mica and consequently the films on glass remained smoother than those on mica. XRD measurements revealed that orientation of the films was stronger on mica than on glass.

(CdSe)ZnS Core−Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites

We report a synthesis of highly luminescent (CdSe)ZnS composite quantum dots with CdSe cores ranging in diameter from 23 to 55 Å. The narrow photoluminescence (fwhm ≤ 40 nm) from these composite dots spans most of the visible spectrum from blue through red with quantum yields of 30−50% at room temperature. We characterize these materials using a range of optical and structural techniques. Optical absorption and photoluminescence spectroscopies probe the effect of ZnS passivation on the electronic structure of the dots. We use a combination of wavelength dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, small and wide angle X-ray scattering, and transmission electron microscopy to analyze the composite dots and determine their chemical composition, average size, size distribution, shape, and internal structure. Using a simple effective mass theory, we model the energy shift for the first excited state for (CdSe)ZnS and (CdSe)CdS dots with varying shell thickness. Finally, we characterize the growth of ZnS on CdSe cores as locally epitaxial and determine how the structure of the ZnS shell influences the photoluminescence properties.

Epitaxial growth of ZnS on bare and arsenic-passivated vicinal Si(100) surfaces

We report a detailed study of molecular beam epitaxial growth of ZnS films on bare and arsenic-passivated vicinal Si(100) surfaces. This study elucidates the initiation of microtwinning and stacking-fault defects on double-stepped substrate surfaces. The study also sheds light on the function of arsenic passivation in reducing crystal defects in ZnS epitaxial layers. Three substrate surfaces, Si(100) 2×1, Si(100):As 2×1, and Si(100):As 1×2, were used for the ZnS epitaxial growth studies. Adsorption experiments were performed to demonstrate the chemical passivation effect of an arsenic overlayer. Reflection high-energy electron diffraction was used to study growth modes and the epitaxial relationship of the ZnS layers to the substrates. Transmission electron microscopy was used to study the crystal-defect structures. Secondary ion mass spectroscopy was used to determine the chemical profiles of the heteroepitaxial interfaces of ZnS layers grown on arsenic-passivated surfaces. One of the main results demonstrated by this work is that thin ZnS films can be grown epitaxially with much better crystal quality on As-passivated Si surfaces than on bare Si surfaces.

Selective Growth Conditions of ZnSe/ZnS Heterostructures on (001) GaAs with Metalorganic Molecular Beam Epitaxy

Selective growth of ZnSe and ZnS on (001) GaAs substrates partially covered with SiOx was examined by metalorganic molecular-beam epitaxy. The growth temperature was the key factor for the selective growth, and the minimum growth temperature of ZnS to achieve selective growth was 450°C. On the other hand, the minimum growth temperature of ZnSe was 500°C. This difference of temperature for the selective growth made it difficult to grow high-quality ZnSe/ZnS heterostructures. To overcome this problem, we used periodic supply epitaxy to lower the selective growth temperature of ZnSe. Supply interruption after short time supply of ZnSe enhances the desorption of precursors especially on SiOx surfaces and this suppresses the nucleation of ZnSe on SiOx surfaces. The lower VI/II ratio also suppresses nucleation of ZnSe on SiOx. The selective growth of ZnSe was thus achieved at 430°C with a VI/II ratio of 1. The minimum selective growth temperature reported on ZnSe up to now is 600°C, and this work demonstrated the selective growth of ZnSe at a considerably lower temperature. We have prepared a ZnSe/ZnS single quantum well (SQW) at 450°C under the selective growth condition and the bright band edge emission from the ZnSe well was observed by photoluminescence measurement at 13 K.

Photo-assisted chemical transport reaction growth of ZnS on GaP

Photo-assisted chemical transport reaction growth of ZnS on GaP

Self‐limiting growth of ZnS on Si substrates at a growth rate of 0.7 monolayers per operating cycle by atomic layer epitaxy using MOCVD

Abstract— ZnS films were grown on (100) Si substrates by atomic layer epitaxy (ALE) using a metal‐organic chemical vapor deposition system. We studied the growth rate as a function of the substrate temperature and the flow rates of DMZn and H2S. The growth rate was kept constant at 0.7 monolayers per cycle and was independent of substrate temperature in the range 125–225°C, and of the mole fractions of both DMZn and H2S. Although the “fractional ALE” growth does not produce a two‐dimensional surface, SEM micrographs show smooth ZnS films with the atomic ratio of S: Zn very close to unity.

In-situ investigations on the SILAR-growth of ZnS films as studied by tapping mode atomic force microscopy

Tapping mode atomic force microscopy (TM-AFM) has been successfully used for in-situ imaging of the deposition of ZnS films with the successive ionic layer adsorption and reaction (SILAR) method. The films were deposited in-situ using the commercial TM-AFM liquid cell as a flow-through reactor. The potential of TM-AFM has been used to study the growth of ZnS on different substrates up to 50 SILAR cycles. Reactants and rinsing water were alternately exchanged in the cell by a computer controlled valve system. In comparison to earlier work performed with the conventional AFM operated in contact mode, imaging artefacts introduced by lateral shear forces can be largely eliminated with TM-AFM. On glass the roughness is observed to decrease initially until typical island formation takes place at a larger number of deposition cycles. On mica island formation can be observed right from the beginning of the process and the roughness increases with increasing number of deposition cycles.

MBE growth of n-type ZnSe and ZnS using ethylchloride as a dopant

A new gas source n-type dopant, ethylchloride (EtCl), was used for MBE growth of ZnSe and ZnS. Carrier concentrations up to 3.2 × 1018 and 3.5 × 1017cm−3 were achieved for ZnSe and ZnS, respectively. The use of the gas source dopant is advantageous in maintaining the MBE chamber.

ALE growth of ZnS 1− xSe x thin films by substituting surface sulfur with elemental selenium

Polycrystalline ZnS 1− x Se x thin films were grown from ZnCl 2, H 2S and Se on soda lime substrates using the atomic layer epitaxy technique. The selenium was incorporated into the films by substituting sulfur atoms on the surface of the growing film with elemental selenium. ZnCl 2 and H 2S pulses were used in every cycle and selenium, which was used only in a certain fraction of the cycles, was always pulsed after H 2S. Growth temperatures were 400 and 500°C. Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy measurements indicated that x in ZnS 1− x Se x can be varied between 0 and 0.8. Interplanar spacings evaluated from XRD data varied linearly as a function of x, thereby verifying the existence of the ZnS 1− x Se x solid solution.

Nucleation Studies Of Zns And ZnO Growth By Chemical Bath Deposition (CBD) On The Surface Of Glass And Tin Oxide Coated Glass

AbstractWe have studied the initial stages of nucleation and growth of ZnS and ZnO on glass and tin oxide coated glass in chemical baths containing thiourea as a source of sulfide ions. The results are used to comment on strategies for the deposition of ZnS and related ternary materials.

Photo-assisted chemical transport reaction growth of ZnS on GaP

Photo-assisted chemical transport reaction growth of ZnS on GaP

Kinetics of chemical beam epitaxy for high quality ZnS film growth

A comprehensive study is reported of the chemical and metalorganic molecular beam epitaxy ( CBE MOMBE ) growth of ZnS on Si and GaAs(100) substrates for applications in advanced electroluminescent displays and for optoelectronic device integration on Si. Growth kinetics studies of conventional and photoassisted MOMBE and CBE using diethylzinc (DeZn) with H 2S, di-isopropylsulfide (DipS) and a novel precursor, t-butyl mercaptan (t-BuSH), are reported. The results obtained indicated that the low temperature growth of ZnS using cracked DeZn and DipS was hindered. This was attributed to the reattachment of the alkyl radicals to surface growth sites, which resulted in a lower growth rate. However, by using uncracked DeZn and H 2S or cracked DeZn and t-BuSH, this growth hindrance was removed by the surface reaction of hydrogen with the alkyl radicals. The addition of a thin CaF 2 buffer layer was found to remarkably improve the growth of ZnS on Si.

Photoluminescence properties of ZnS epilayers grown by metalorganic molecular beam epitaxy

A comprehensive study is reported of the epitaxial growth and photoluminescence properties of ZnS on GaAs and Si. Conventional and photoassisted MOMBE and CBE growth using H2S, DipS and t-BuSH, with DeZn showed higher growth rates in the presence of H, or under photoassisted conditions. At low temperatures, the radical alkyl by-products from the cracked precursors were identified as reducing the growth rate through surface site blocking. A CaF2 buffer layer was shown to improve the crystalline quality due to elimination of a reaction between S and Si. Low temperature photoluminescence studies identified recombinations from the ground and the first excited states of the free exciton as well as from neutral donor and acceptor bound excitons, and phonon replicas.

Temperature Dependence of ZnS Growth with Atmospheric-Pressure Metalorganic Vapor Phase Epitaxy Using Ditertiarybutyl Sulfide

Quadrupole mass spectrometric study of the decomposition of ditertiarybutyl sulfide (DtBS) showed that DtBS decomposes at low temperatures above 300°C. The growth of ZnS with metalorganic vapor phase epitaxy (MOVPE) using diethylzinc (DEZn) and DtBS showed the growth rate of more than 1 µm/h at ∼300°C with moderate flow rates of the precursors. These studies demonstrate the superiority of DtBS for low-temperature growth of S-containing II-VI semiconductors. However, the decrease of the growth rate was observed at higher temperatures under the growth condition limited by DtBS supply. We examined the reason for this phenomenon and attributed it mainly to the decrease of the transport efficiency of DtBS to the growing surface due to thermal cracking of DtBS during transport, which was caused by the excessive difference between the growth temperature and the decomposition temperature of the precursor.

Growth of ZnS and ZnSSe by gas-source molecular beam epitaxy using hydride group VI sources

ZnS and ZnSSe layers were successfully grown by gas-source molecular beam epitaxy using hydride H 2S and H 2Se sources, and their surface morphology was very smooth. The full width at half maximum of X-ray rocking curve of the ZnS x Se 1- x layer with S composition x of 0.06 (lattice-matching to a GaAs substrate) was as low as 22 arc sec. For the ZnSSe layer, the electron concentration was controlled in a 10 17 cm -3 range by using n-type dopant gallium, and a net acceptor concentration of 7.4 × 10 17 cm −3 was obtained by using active-nitrogen as p-type dopant. Using n- and p-ZnSSe layers, separate-confinement-heterostructure multiple-quantum-well laser diodes were fabricated. Lasing operation was observed by injecting a pulsed current at 77 K.

Atomic layer epitaxy growth of ZnS on (100)GaAs using molecular beam epitaxy system

The atomic layer epitaxy (ALE) growth of monocrystalline ZnS is successfully carried out onto (100)GaAs substrates at 185–;200°C by the use of a molecular beam epitaxy system, and the growth mechanism is considered with the results of reflection high energy electron diffraction (RHEED). The ALE growth is performed with alternative irradiations of Zn and S molecular beams. The orientation of the epilayer is 〈100〉 and the epilayer is free from twins. The RHEED patterns suggest that the progress of the growth of ALE-ZnS is based on the alternative change of the surface structures of c(2 × 2)-Zn and (2 × 1)-S. The growth rate per cycle is remarkably dependent on the substrate temperature and the origins of the growth rate variation are presumably due to the temperature dependences of the dissociations of cluster molecules or polyatomic molecules and of sticking coefficients for Zn and S.

Growth of II–VI compounds by metal–organic chemical vapour deposition. Propylene sulfide: a novel sulfur-containing precursor for MOCVD growth of ZnS

As part of our continuing investigations into the problem of pre-reaction in MOCVD systems, layers of ZnS have been grown onto GaAs substrates using Me2Zn and the novel sulfur-containing precursor propylene sulfide. Layers have been produced in the temperature range 300–550 °C and have been characterized by XRD. The results indicate that the layers with the highest degree of crystallinity are grown towards the higher end of this temperature range. Most significantly, no pre-reaction is observed between these precursors.