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.

Atomic Layer Epitaxy is a stepwise deposition process by supplying the sources materials alternatively. This deposition technique provides the monolayer control of film thickness and the uniform film growth over a large area. ZnSxSe1-x layers were grown epitaxially onto Si and GaAs substrate by using DMZn and H2S , H2Se gases for the reactant source. Owing to the self-limiting characteristics of ALE process, ZnSxSe1-x monolayers could be deposited over a wide range of temperature within growth window. In this study, for obtaining high crystalline quality ZnSxSe1-x epitaxial films, various growth conditions were investigated including substrate temperature, the flow rate of DMZn, H2S and H2Se, H2 purge duration and pulse duration etc.. A thermodynamic analysis based the calculation of Seki et. al [6], was used to investigate the effects by varying the substrate temperature, input mole ratio of group VI source gases on equilibrium partial pressure, solid composition and solid-vapor distribution relation of this alloy. The interaction parameter of ZnSxSe1-x, £[, was estimated by using the delta-lattice parameter (DLP) model suggested by Stringfellow [39]. Finally, it shows that the thermodynamic analysis provides a useful guideline for the growth of ZnSxSe1-x alloy on Si and GaAs substrates.