Zinc selenide (ZnSe) film is successfully deposited by the electrodeposition technology. Due to ZnSe with a direct band-gap of 2.7 eV, it is widely used for optoelectronic applications. Recently, it is used as the window layer to improve the open circuit voltage in solar cells. The ZnSe film was prepared with vacuum, high temperature, and high pressure was usually used. However, these disadvantages limited the cost down and time to market. Electrodeposition is an easy use and very simple technology proposed to grow large area of ZnSe films. In this study, the electrodeposition of ZnSe film has been accomplished in an aqueous bath (pH = 2) during electrochemical reduction of an electrolyte containing SeO2 (100 mM) and ZnSO4¡E7H2O (1 M) on a indium tin oxide glass substrate. Results clearly show that the film quality was strongly depend on the electrodeposited potential. The electro-potential is Indeed as a function of the substrate temperature, the concentration of solutes, and pH value of solution. The structure of as-deposited ZnSe thin film is polycrystalline measured by x-ray diffraction (XRD). The surface morphology of deposited films are investigated by Scanning electron microscopy (SEM). The high quality of film growth is achieved when the electro-potential applied is close to the electrodeposited potential of ZnSe. As the more negative of electrodeposited potential applied at room temperature, the growth rate, thickness and resistance of thin film are increase and the current is decrease. In addition, the i-t curve shows very rough due to the bubbles generated to disturb the solution while electrodeposited at the high temperature.

The research and development of zinc selenide (ZnSe) based wide-gap II¡VVI materials and related blue/green light-emitting devices have significantly progressed since 1990. ZnSe is also a promising material for use in windows, lenses, output couplers, beam expanders, optically controlled switching, visible transmission and giant photo-resistivity. Recently, ZnSe has become an important material used as the window layer of CuInSe2-based solar cells . To improve device performance, it is necessary to reduce interface defects and improve epitaxial layer quality. However, ZnSe thin films on glass substrates with high reliability and applicability have not yet been developed. In this study, a ZnSe buffer layer was firstly grown by SME during the initial stage of film growth; the film crystallinity could gradually be improved layer by layer with smaller thicknesses. While the lattice disorder of the buffer layer decreased rapidly after several cycles of SME growth, the interfacial lattice mismatch between the buffer layer and the ZnSe film deposited by MBD was reduced. Thus, ZnSe films with buffer layers demonstrated better crystallinity. Initial growth stage evaluation of high-quality ZnSe films deposited on glass substrate was investigated. The self-limiting monolayer epitaxial (SME) process was used to pre-growth the buffer layer for a zinc selenide (ZnSe) film deposited. After alternating depositions for several cycles, the growth mode was changed to the molecular beam deposition (MBD) mode under growth conditions. Films deposited at substrate temperatures of 250¡V350¢XC and Se/Zn beam equivalent pressure (BEP) ratios of 0.77¡V1.87 were investigated. The crystal structure and preferred orientation of as-grown ZnSe films were examined using X-ray diffraction (XRD) patterns. The optical properties of the ZnSe films were revealed by photoluminescence spectra. The structure properties of as-deposited ZnSe films have been measured by X-ray diffraction (XRD) technique. The optimum film growth condition has been determined rapidly by comparing and analyzing the relative full width at half-maximum (FWHM) and peak intensity of XRD spectra. The composition of ZnSe films is determined by energy dispersive spectroscopic (EDS) analysis. Optical properties of ZnSe films are characterized by photoluminescence spectra. In addition, the structural parameters, crystallinity, lattice constant, grain size, strain, dislocation density and orientation of ZnSe film calculated are correlated with their growth conditions. The characteristics of the ZnSe films with and without a buffer layer were compared and discussed in detail. Finally, our results demonstrate that how the quality of ZnSe film can be improved on glass substrates for application to various devices.

ABSTRACT Recently, there has been an increasing interest in the fabrication and theory of self-assembled quantum dots (SAQD). Self-assembled quantum dots are of great interest because of good optical properties and device applications such as quantum dot lasers and memory device. The main merit of laser based on quantum dot is both the low threshold current density and low temperature sensitivite. We can grow the ZnSe quantum dot on GaAs substrate. The maximum value of dots density is 1.3¡Ñ109cm-2 at 16.7 of ¢¾/¢º ratio. The dots densities are increasing by the flow rate of DEZn and H2Se. When the ¢¾/¢º ratio are lager than 16.7 or smaller than 7.5 will lead to quantum dots increasing. The blue shift is from 8 nm to 15 nm by quantum confinement. The high quality of ZnS0.81Se0.19 epilayers on GaP substrate are grown with DEZn, H2Se, H2S and H2 fixed at 2.4 sccm, 10 sccm, 10 sccm and 1 slm respectively, and prepared at 340¢J and 50 min. High quality ZnS0.81Se0.19:N epilayer which was lattice-matched to GaP substrate has been prepared. The FWHM of X-ray diffraction was 720.2 arcsec. Its R-value was 5.20%. Then we grow ZnSe quantum dots / ZnS0.81Se0.19/GaP. The largest density of quantum dots is 1.1¡Ñ109 cm-2 at 30 s growth time.

In this thesis, ZnSe self-assembled quantum dots (SAQDs) was grown on GaAs substrate by organic-metal vapor phase epitaxy (OMVPE) with Stranski-Krastanow (S-K) growth mode. The contact-mode atomic force microscopy (AFM) and photoluminescence (PL) are used to measure the surface morphology and optical properties of ZnSe SAQDs, respectively. Experimental data show that the flow rate of H2Se have a significant influence on the relation between the density and the growth temperature of ZnSe SAQDs. At the H2Se flow rate of 25 sccm, the density of ZnSe SAQDs increases up to 3.96¡Ñ108 cm-2 as the growth temperature increase from 140¢J to 380¢J. However, the growth temperature has a negligible effect of the density of ZnSe SAQDs at the flow rate of 30 sccm. At the H2Se flow rate of 40 sccm, the density of ZnSe SAQDs decreases as the growth temperature increases due to the coalescences of SAQDs. Furthermore, a cap layer of ZnS was deposited on ZnSe SAQDs. Experimental data indicate that the increase of the thickness of ZnS cap layer results in blue-shifted emission due to the ZnSe SAQDs experience more biaxial strain. Besides, the ZnS cap layer provides an additional source of carriers, which thermalize to the ZnSe SAQDs before recombination, resulting in a significantly stronger photoluminescence signal. In AFM images, the density of ZnSe SAQDs decreases as the increase of the thickness of ZnS cap layer. In conclusion, we have successfully grown the high density of ZnSe SAQDs on the GaAs substrate and deposit the ZnS cap layer on it. Based on the technique, the multi-quantum dots will be developed in the future.

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Zinc selenide is a wide bandgap II-VI semiconductor. The minimum bandgap at £F point (zone center) is direct and has a room temperature value of 2.67eV, corresponding to the blue region of the visible spectrum (464nm). Molecular beam epitaxy (MBE) is an ultra high vacuum technique used for the growth of semiconductors. The molecular beam epitaxy system used for the growth of semiconductors . The molecular beam epitaxy system used for growth of the II-VI semiconductor layers is described in detail in Chapter 2. Chapter 3 describes the substrate preparation procedure and growth of ZnSe epitaxial layers. Last, information from characterization technique has been used to analysis the quality of the layers and hence determine referred growth conditions.

We have studies the II-VI ternary compound semiconductor ZnSe grown by molecular beam epitaxy ¡]MBE¡^Method. The modulation spectroscopy was used to study ZnSe. ZnSe epilayer was grown on GaAs substrate. The lattice mismatch¡]0.27 ¢H¡^between GaAs and ZnSe create a strain at the GaAs/ZnSe interface. The strain will remove the degeneracy of heavy and light holes to conduction band transition energies. We use the photoreflectance to measure the energy of different thickness ZnSe epilayers at low temperature. It was found that as the epilayer thickness becomes larger, the£GE will become smaller. We have also analyzed the energy of different temperatures in terms of Varshni relation, and the temperature dependence of the broadening parameters.

The method of C-V analysis is a powerful technique to determine the parameter of MOS (metal oxide semiconductor) structure. In this study, we fabricate the MOS structure with rf magnetron sputtering of Ta2O5 on n-ZnSe surface. The n-ZnSe¡¦s with various carrier concentrations have different electrical property. Interfaces of various Ta2O5/ZnSe have different properties, for examples flatband voltage, threshold voltage, the mobile oxide charge density, and the effective oxide charge concentration and etc. We find that the interfaces of the Ta2O5/ZnSe MOS structure have low mobile charges and interface trap charges. Thus Ta2O5/ZnSe MOS structure may be worthy to develop further.

Abstract High quality epitaxial growth of undoped ZnSe, ZnSxSe1-x and ZnSe-ZnS strained quantum well structures were successfully grown on n-type (100)-oriented silicon substrates at 150 ºC in a horizontal cold-wall quartz reactor by low-pressure metalorganic atomic layer epitaxy (MOALE) at a pressure of 30 Torr for the first time. Dimethylzinc [Zn(CH3)2, DMZn], hydrogen selenide (H2Se) and hydrogen sulfur (H2S) were used as the reactants. ALE is a suitable technique for the growth of ultra thin semiconductors because it provides accuracy monolayer control of the deposited film thickness, low growth temperature and uniform growth over a large area by its¡§ self-limiting mechanism ¡¨via supplying source materials in a flow pulse sequences alternatively over the substrate. Idea one monolayer per cycle was obtained in wide range of parameters such as substrate temperatures, mole flow rate and pulse duration of reactants. From X-ray diffraction pattern, (400)-oriental single crystal epilayers of ZnSe are evidenced. The surface morphologies of ZnSe in the ALE temperature region 150 - 200 ¢J, extensively smooth and mirror-like surface were obtained. PL spectra of ZnSe epilayer is dominated by the strong near-band-edge at 2.8 eV with FWHM of 36 meV. Schottky diodes were fabricated from the undoped ZnSe layer and the electrical properties were measured at room temperature. From the current-voltage (I-V) characteristics, a high reverse breakdown voltage (>40 V) and an excellent low cut-in voltage of 0.6 - 0.8 V were obtained. On the basis of the observed ZnSe/Si epitaxial film properties, the material is suitable for fabrication of ZnSe-based blue light emitting diodes and for application in direct-current thin-film electroluminescence. The lattice of the ZnSxSe1-x layer with a sulfur content around 93% was found to have the best match to the Si substrate, as confirmed by the good layer thickness, uniformity, surface morphology and narrow linewidth of the X-ray diffraction rocking curve with a minimal FWHM of about 0.16 degree. In addition, strong near-band-edge and weak deep-level emissions in the longer wavelength region dominate PL spectra of the ZnS0.93Se0.07 epilayer at 300K. With respect to Schottky diodes, Au/n-ZnS0.93Se0.07/Al, has a high breakdown voltage, over 40 V at 400 nA and a low cut-in voltage of 0.68 V. The highest Hall mobility of the ZnS0.93Se0.07 is 347 cm2/v-sec. These results indicate a good lattice-match of ZnS0.93Se0.07/Si as a result of low numbers of interface and epitaxial layer defects. The lower temperature of ZnSe-ZnS strained quantum well structures, 150 ºC would be lowed enough to eliminate 3-D growth related to the lattice mismatch between ZnSe and ZnS. A good epitaxy and crystallinity was carried out by X-ray diffraction. The formation of the strained quantum well structure is evident from the periodic behavior of each fluctuation profile by SIMS. At least 25 periodic thickness of the ALE growth samples shows a strong blue emissions and nearly neglects the deep-level emission at room temperature. The phenomenon of quantum size effects and the ¡§ blue-shift ¡¨ was evidenced as the well width increases. The results of the PL measurements were found to correlate well with the theoretical one, parabolic well-strain mode. Schottky diodes were fabricated from the Au/ZnSe-ZnS SMQW/n-Si/Al, a high reverse breakdown voltage over 40 (at 20 µA) and an extremely low cut-in voltage of 80 - 120 mV were obtained. The I-V characteristics of the heterojunction are more suitable for the fabrication of the direct-current thin film electroluminescent (EL) device.