Epitaxial Growth Of ZnSe Research Articles

Photoelectric converters with graded-gap layers based on ZnSe

Oriented polycrystalline CdSe layers are used as substrates for the epitaxial growth of ZnSe. In order to exclude the formation of defects due to mismatch between lattice constants of the active epitaxial layer and the substrate material, a graded-gap CdxZn1 − xSe interlayer is grown. In this structure, the growth of donor-type point defects from the substrate through the growing layers leads to the appearance of a low-resistivity ZnSe layer. A barrier-forming p-Cu1.8S layer is deposited onto the ZnSe. In order to reduce the recombination losses of photocarriers at the p-Cu1.8S-n-ZnSe interface of the surface-barrier converter, an additional thin graded-gap layer incorporated into the space-charge region of the photoelectric converter is suggested and implemented.

Epitaxial growth of ZnSe on GaAs with the use of the ZnSe compound as the source

Processes of the molecular-beam epitaxy of submicron layers of ZnSe on GaAs (001) substrates with the use of the ZnSe compound as the source have been investigated depending on the initial state of the substrate surface and its temperature. It is shown that after the formation of the heterointerface the “excess” Ga remains on the surface of the growing film, determining, at temperatures above 250°C, the rate of its growth. According to the experimentally measured spectra of low-temperature luminescence, the optimum temperature of obtaining layers by this method is 240°C.

Design and Synthesis of High-Quality CdS/ZnSe Type-II Core/Shell Nanocrystals

High-quality (narrow size distribution, high crystallinity, high luminescent efficiency) type-II core/shell nanocrystals have been designed and prepared based on ZnSe epitaxial growth around CdS core template. The CdS/ZnSe type-II core/shell nanocrystals were prepared by the alternate injection of Se/Zn precursors into a diluted pre-prepared CdS core nanocrystals reaction solution via the successive ion layer adsorption and reaction (SILAR) technique. The claimed core/shell structure was confirmed by the optical spectra, TEM analysis and XRD measurement. The emission colors of the obtained CdS/ZnSe nanostructures can be tuned from 510 nm to 590 nm by the variation of both the size of the CdS core and the thickness of the ZnSe shell. The photoluminescence properties of the obtained CdS/ZnSe core/shell nanocrystals (emission efficiency up to 50%) are comparable to the best result reported for the extensively studied CdSe based nanocrystals.

Electrochemical Deposition of ZnSe from Dimethyl Sulfoxide Solution and Characterization of Epitaxial Growth

In this work, we studied the conditions for the electrodeposition of ZnSe films from dimethyl sulfoxide solutions with a special focus on epitaxial growth. We examined the influence of experimental parameters such as the nature of the substrate, temperature, and hydrodynamic conditions. The investigated substrates were glass covered with SnO2:F, molybdenum and (1̄1̄1̄) or (100) n−InP substrates. The voltammetric behavior of the Zn(II)−Se−DMSO system showed that the mechanism of ZnSe film formation is strongly dependent on the nature of the substrate. Films prepared at constant potential were characterized by scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), atomic force microscopy (AFM), reflection of high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and also by optical measurements. Epitaxial growth of ZnSe was obtained on (100) and (1̄1̄1̄) n−InP crystalline planes with good quality as demonstrated by RHEED patterns and TEM measurements, a result that confirms that electrodeposition provides an alternative route to obtain epitaxial films of ZnSe.

Ab initio molecular orbital study on atmosphere-sensitive characteristics of the alternate supply OMVPE growth of ZnSe

An insight into surface chemical reactions responsible for the organometallic vapor phase epitaxial (OMVPE) growth of ZnSe under the alternate supply of diethylzinc (DEZn) and dimethylselenium (DMSe) was provided by theoretical interpretation of our previous experimental results. Based on a quantum chemical study, atmosphere-sensitive characteristics of ZnSe growth were attributed to differences in the pathways and the corresponding adiabatic potential barriers between diethylzinc chemisorption onto hydrogen- and methyl-terminated Se-stabilized ZnSe surfaces.

The reaction mechanisms for precursors in photo-assisted metalorganic-vapor-phase epitaxy growth of ZnSe

The epitaxial layers of ZnSe have been grown by photo-assisted metalorganic-vapor-phase epitaxy with the use of dimethylzinc and dimethylselenide as precursors, and the growth mechanism has been investigated. The decomposition of precursors was observed by in situ measurements of ultraviolet photoabsorption spectra. The results show that dimethylzinc is decomposed by reaction with hydrogen molecule and dimethylselenide is decomposed by photocatalysis on the surface of ZnSe. New reaction models are proposed.

Characterization and fabrication of ZnSe epilayer on porous silicon substrate

This paper reports the development of a ZnSe epilayer onto porous silicon with a chemical vapor deposition (CVD) system to obtain a single crystal ZnSe epilayer on a silicon substrate for low cost short wavelength device applications. The ZnSe single crystal epilayer was successfully grown onto porous silicon. The optimized silicon substrate anodization conditions for ZnSe epitaxial growth are J=40 mA/cm 2, HF/C 2H 5OH=5:5 for the n-substrate and J=30 mA/cm 2, HF/C 2H 5OH=3:2 for the p-substrate. The PL spectrum of the ZnSe single crystal epilayer at 10 K has four peaks located at 444 nm (2.793 eV), 457 nm (2.718 eV), 478 nm (2.594 eV), and 574 nm (2.16 eV), respectively.

Molecular-beam epitaxy growth and nitrogen doping of hexagonal ZnSe and ZnCdSe/ZnSe quantum well structures on hexagonal ZnMgSSe bulk substrates

Hexagonal ZnMgSSe bulk substrates have been synthesized as attractive alternatives for the homoepitaxial growth of II–VI device structures. Hexagonal ZnSe epilayers and ZnCdSe/ZnSe quantum well structures were grown on these substrates by molecular-beam epitaxy. The cross-sectional transmission electron microscopy image shows that the ZnSe epilayer replicated the hexagonal structure of the substrate. The 6 K photoluminescence (PL) spectra of the hexagonal ZnSe layers show strong impurity-bound-exciton emissions at about 2.796 eV. No Y-line (defect-related emission) is observed in the spectra suggesting good substrate preparation and growth conditions. The 77 K PL spectra of hexagonal quantum well structures show dominant emission from the ZnCdSe well layer. Double-crystal x-ray rocking curves indicate that the ZnSe epitaxial layers and the substrates are near lattice matched. Doping of hexagonal ZnSe with nitrogen was performed. Photoluminescence spectra suggest that these samples exhibit donor-acceptor-pair emission with typical characteristics of heavily doped (compensated) samples.

Importance of initial nucleation step on low temperature photoassisted MOVPE growth of ZnSe

In this work, low temperature photoassisted metal-organic vapor phase epitaxy (MOVPE) growth of ZnSe on GaAs was carried out using dimethylzinc (DMZn) as the Zn precursor and dimethylselnium (DMSe) or diethylselnium (DESe) as the Se precursor at atmospheric pressure under H2 carrier gas, using the 458 nm wavelength from an Ar+ laser. In situ laser interferometry showed that the growth rate for thin films is non-linear and was explained in terms of the efficiency of coupling of the photo-irradiation with the growing film. The growth rate (GR) can be described by GR = P η F (1 − exp (−α d)) where η is the photo-chemical quantum efficiency, d is the film thickness, F is a structural factor, P is the laser intensity and α is the absorption coefficient. In situ laser interferometry has been essential in making these measurements to observe the initial non-linearity and ensure that characteristic growth rates are taken from steady state growth. Growth using DMSe as the Se precursor was very photosensitive due to its higher photochemical quantum efficiency arising from the additional source of CH3. radicals. These layers were mostly rough due to the slight variation in laser intensity across a region giving different degree of enhancement which is magnified by the growth rate non-linearity leading to non-uniform, and roughened growth. In the case of growth using DESe, it was possible to grow an initial nucleation layer of ZnSe pyrolyticaly prior to photo-assisted growth which ensured that there was sufficient thickness, d, of ZnSe such that the exponential term in the above equation became negligible and the growth rate was dependent only on the linear terms. The slight variation in laser intensity across the surface does not then cause a very significant variation in growth rate, thus maintaining smooth morphology and uniform growth rate.

Si substrate treatment with nitrogen for molecular beam epitaxial growth of ZnSe

The authors have achieved a substantial improvement in the ZnSe molecular beam epitaxy of Si(111) by irradiating the substrate surface with a flux of nitrogen free radicals (N*) prior to growth. This new substrate treatment induced an initial two-dimensional growth as revealed by reflection high-energy electron diffraction, Auger electron spectroscopy, and atomic force microscopy. The improved epitaxy was confirmed by high resolution x-ray diffraction.

Simulations of [formula omitted] heteroepitaxial growth

The epitaxial growth of ZnSe on GaAs(0 0 1) is simulated by employing a hybrid approach based on molecular dynamics to describe the initial kinetic behavior of deposited adatoms and Monte Carlo displacements to account for subsequent equilibration. Stillinger-Weber potentials are employed to describe interatomic interactions. This method is well-suited to describe initial nucleation and growth. Results for a variety of growth temperatures and interface structures are presented.

Molecular beam epitaxial growth of ZnSe(1 1 1) films on GaAs(1 1 1)B substrates and nitrogen doping

Abstract ZnSe films were grown on GaAs(1 1 1)B substrates by molecular beam epitaxy. The observation of reflection high-energy electron diffraction confirmed that the epilayers on both just and 10 o -misoriented (1 1 1)B substrates consist of twins. The photoluminescence of the undoped epilayers showed defect-related Y-line emissions and deep emissions owing to the twins. Nitrogen was doped to the epilayers using an RF plasma cell. The photoluminescence spectra of the doped epilayers suggested that the nitrogen doping to ZnSe is enhanced using the GaAs(1 1 1)B substrates instead of the GaAs(1 0 0) substrates. We discussed the reason based on the bond number of the growing surface.

Molecular beam epitaxial growth of ZnSe on GaAs substrates: influence of precursors on interface quality

The initial growth of thin ZnSe layers, grown on GaAs(0 0 1) using molecular beam epitaxy (MBE), has been studied using real-time reflection high-energy electron diffraction (RHEED), as well as X-ray double-crystal rocking curves (DCRC), reflectivity difference spectroscopy (RDS) and transmission electron microscopy (TEM). A noticeable difference in interface quality and growth was observed depending upon the initial precursor. Exposure to Se flux before growth led initially to three-dimensional growth, whereas exposure to Zn flux or no precursor led immediately to two-dimensional growth. X-ray DCRC and RDS confirmed that the overall sample quality was better with two-dimensional growth, and TEM observations were consistent with previous studies which have shown that initial three-dimensional growth is related to the formation of Ga2Se3 at the interface, leading to high densities of stacking faults and edge dislocations.

ZnSe epitaxial growth on Si(100) and Ge(100) by H-radical assisted MOCVD

Epitaxial ZnSe is a polar material grown on non-polar substrates such as Si(100) and Ge(100) by metal organic chemical vapor deposition methods. Epitaxial growth of ZnSe on non-polar materials is more difficult than on polar materials, for example, on GaAs. For the growth of ZnSe on non-polar substrates, a polarization of substrate surface at the initial step is of importance. The FWHM of XRD peak obtained for ZnSe(100) grown on Ge is wider than that obtained for ZnSe(100) grown on GaAs, in spite of both Ge and GaAs having nearly the same lattice constant. Further, the surface morphology of ZnSe films grown on Ge and GaAs substrates is observed to be different. It is considered that the surface polarization of Ge substrate at the initial stage is not uniform. This results in a lower number of growth sites on Ge substrate compared with that on GaAs substrate.

ZnSe epitaxial growth on zinc- and selenium-treated GaAs(001) surfaces observed by STM

The structures of both selenium and zinc treated GaAs(001) surfaces and the early stages of ZnSe growth on those surfaces have been studied using reflection high energy electron diffraction (RHEED) and in-situ scanning tunneling microscopy (STM). Upon exposure of Se, both Ga- and As-stabilized GaAs surfaces form (2 × 1) structures which were observed by RHEED at a temperature range of 250–500°C. The STM image revealed that the Se-terminated surface is well ordered and has dimer rows along the [110] direction in higher treatment temperatures. During the ZnSe growth on the Se-terminated surface, the RHEED pattern immediately became spotty (only 1–2 ML of growth). STM images of this surface showed a disordered rough surface. Thus, it was confirmed that epitaxy of ZnSe film on Se-terminated GaAs proceeded by predominantly three dimensional island growth. In the case of Zn exposure on As-stabilized (2 × 4) surfaces, there were no obvious changes in the STM image and RHEED patterns. Only a slight change was observed in the 2 × reconstruction pattern. The streaks were weaker and the spots at the Laue zone became brighter. This implies that Zn did not react with the GaAs surface but merely stuck to it. At ∼ 0.5 ML of ZnSe growth on the Zn-treated surface, streaks along the 4 × direction became weaker and the STM showed a very uniform distribution of ZnSe. The (2 × 4) stripes were still observed. This is in good agreement with a two dimensional growth mode.

Impact of surface stoichiometry control during the initial stages of growth on the stacking fault concentration in ZnSe epilayers grown by molecular beam epitaxy

We have determined that the surface stoichiometry maintained during the first five monolayers of ZnSe epitaxial growth can have a significant influence on the stacking fault concentration in 2 μm thick epilayers. In particular, we have been able to minimize the stacking fault concentration to a level in the 104 cm−2 range (comparable to the stacking fault concentration in the ZnSe substrates used for epitaxy) by appropriate selection of a delay time (∼30 s for a substrate temperature of 300 °C) employed during an alternate element (Zn and Se) exposure phase of growth. The delay time in question is the time elapsed between closing the Se shutter and opening the Zn shutter. We show that the surface stoichiometry (Zn to Se atomic ratio) can be tailored during the delay phase since Se thermal desorption occurs at the growth temperature in a controlled fashion from an initially Se-terminated surface, and, it is postulated that selection of an optimum delay time corresponding to the attainment of a near-stoichiometric surface results in the growth of low stacking fault concentration material.

Atomic Layer Epitaxy Growth of ZnSe on (100) GaAs Using Metalorganic Vapor-Phase Epitaxy System

The atomic layer epitaxy (ALE) growth of ZnSe is successfully carried out on (100) GaAs substrates at 100–200° C by the use of a metalorganic vapor-phase epitaxy system. The growth rate per cycle is strongly dependent on the substrate temperature. The self-limiting growth of one monolayer per cycle is obtained in the wide substrate temperature range of 100–200° C. Double-crystal X-ray pattern shows that the lattice constant of ZnSe epilayer is 5.69 Å. The surface morphologies are smooth and mirrorlike. The photoluminescence spectrum shows an emission at 443 nm at 77 K.

ZnSe crystal growth by radical assisted MOCVD

Epitaxial growth of ZnSe on silicon substrates was studied by metal organic chemical vapor deposition (MOCVD), using diethylzinc (DEZ) and selenium hydride (SeH 2). During the epitaxial growth, hydrogen radicals or nitrogen radicals were introduced and showered on the growing surface. The growth rate was extensively increased in the presence of H radicals produced by the rf plasma. Heteroepitaxial growth of ZnSe on silicon appeared at the substrate temperatures above 400°C. When H radicals were replaced by N radicals produced by NH 3 plasma, N-radical doping into ZnSe which is promising to yield p-ZnSe was observed.

Surface migration of ZnSe regrowth using compound source molecular beam epitaxy

We studied ZnSe epitaxial growth on ZnSe and ZnSSe patterned layers with two methods. One was conventional-type molecular beam epitaxy (MBE) which uses elemental materials as its sources. The other one was compound source molecular beam epitaxy (CSMBE) which uses compound polycrystals. We found that the epilayer is regrown on undercut mesa sidewall by CSMBE, while nothing is grown on the sidewall by conventional MBE. The surface migration length on ZnSSe (221)B plane was estimated from the surface edge profile of the regrown layer by CSMBE.

Surface reactions in photoassisted MOVPE growth of ZnSe as studied by in-situ optical reflection measurements

Optical reflection measurements were performed during metalorganic vapor phase epitaxy (MOVPE) growth of ZnSe at a variety of source supply modes, i.e., simultaneous and alternate supplies of diethylzinc (DEZn) and dimethylselenide (DMSe), and with and without above-bandgap photoirradiation. Reflection change took place at an interval of the DEZn supply in an alternate source supply mode, while it did not at an interval of the DMSe supply. On the other hand, the reflection signal induced by the DEZn supply tended to fall off unless the DMSe supply followed immediately. The observed results suggest that the formation of a precursor in the simultaneous presence of DEZn and DMSe on the surface is responsible for photoassisted growth rate enhancement.