G. S. Tompa

Transparent and conductive Ga-doped ZnO films grown by low pressure metal organic chemical vapor deposition

Highly transparent conductive Ga-doped zinc oxide (ZnO:Ga) has been deposited on 3 in.×4 in. Corning 7059 glass and other substrates using a high speed rotating disk reactor low pressure metal organic chemical vapor deposition system. Diethylzinc, oxygen, and triethylgallium were used as precursors. The films exhibit low resistivity, ∼2.6×10−4 Ω cm, high optical transparency (>85%) in the visible range, good adhesion, and are highly stable. The film properties were correlated with the growth conditions, including flow rate, temperature, pressure, and doping concentrations. The microstructural properties of the films, such as surface and interface morphology, crystallinity, and composition were studied using scanning electron microscopy, x-ray diffraction, and secondary ion mass spectroscopy. The resistivity and transmittance of the films were investigated by four-point probe measurements, photoluminescence spectroscopy, and optical absorption spectroscopy. In order to meet the needs for application to fla...

Influence of the size dispersion on the emission spectra of the Si nanostructures

A systematic study of the size dependence of the photoluminescence spectra of Si quantum nanocrystals in the SiO2 matrix has been performed. The results have been fitted to a quantum‐confinement model that includes the nanocrystal size dispersion rather than a specific size of the nanocrystal. This, in conjunction with the results [Z. H. Lu, D. J. Lockwood, and J.‐M. Baribeau, Nature 378, 258 (1995)] for amorphous Si layers serves as a strong confirmation of the confinement‐induced nature of the photoluminescence.

Silicon and germanium nanoparticle formation in an inductively coupled plasma reactor

We have studied the formation of Si nanoparticles in a SiH4–Ar plasma discharge generated in a helical resonator type inductively coupled plasma reactor. It is observed that Si particles vary in sizes from 5 to 15 nm under different conditions. The particles were mostly spherical and made up of a crystalline core with a 1–2 nm thick amorphous shell. The size distribution was narrow for particles formed at a pressure of 200 mTorr, plasma power of 400 W and silane flow rate of 20 sccm (+980 sccm Ar). The effect of a dc bias applied to the particle collecting grids has also been studied. It is found that a negative bias (−25 to −100 V) applied to the grids used for particle collection results in a large increase in the number of Si nanoparticles collected, while a positive bias does not change the collection efficiency considerably, suggesting that the particles are positively charged. Under very low flow rates and under high plasma powers, the Si particle density decreases considerably and a film like depos...

Photolumineseence, Electroluminescence, and Cathodoluminescence of ZnO:Zn Phosphor Films Prepared by MOCVD

Cathode ray tube (CRT) technology remains the major display component for todays display technologies. The improvements from monochrome displays to todays full color displays have always been accompanied by improvements in the phosphors. The CRT type displays operate at very high voltages (over 10 keV) at relatively low currents, a few microamps/cm 2 . The phosphors and phosphor coating technology used in CRT based displays have been optimized for operation with these excitation conditions. However, the developments of field emitter displays based on microtip technology, or negative electron affinity technology require phosphors that operate at lower voltages, preferably 10 to 1500 eV at relatively higher current densities. Zn-rich zinc oxide (ZnO:Zn) powders have shown improved low voltage cathodoluminescence (CL) as compared to conventional ZnS based phosphors. ZnO:Zn thin film phosphors for cathodoluminescent displays, compared to conventional powder phosphors, can have the advantages of high electrical and thermal conductivity, high energy saturation limit, and high screen resolution. The photoluminescence (PL), Electroluminescence (EL), and CL from thin ZnO:Zn films were studied. The samples were prepared by Low Pressure Metal Organic Chemical Vapor Deposition (LP MOCVD) and post-annealed at temperatures from 700 °C to 1000 ° C. The PL, EL, and CL spectra have a peak centered at 590 nm that increases with annealing temperatures up to 1000 °C. The CL efficiencies are 0.12 Lm/W at electron voltages and currents as low as 500 V and 64 mA/cm 2 . The ZnO films have been characterized by X-ray Diffiractometry (XRD), and Sweep Electron Microscope (SEM). These PL, EL, and CL results from ZnO:Zn films show the promise for improved phosphors to meet Field Emitting Device (FED) challenges.

Elemental vapor transport epitaxy of GaAs, without oval defects

A novel, high yield, vacuum growth technique, elemental vapor transport epitaxy (EVTE), is reviewed and materials results are presented. In EVTE, vapors are transported from remote elemental source reservoirs and feed through regulating valves into a common hot manifold which is located directly beneath the inverted wafer. Film uniformity is controlled by the flux distribution from the common manifold. Using the hot flux manifold we have demonstrated oval defect‐free growth of specular GaAs films on 2 in. diam (100) and (111) 2° off substrates at growth rates exceeding 1 μm/h to several microns of thickness. Without the flux manifold, under similar growth conditions, the films are observed to have many oval defects. The technique offers the safety of the molecular beam epitaxy process without the oval defects and the flux control of the organometallic vapor phase epitaxy/chemical beam epitaxy processes without the carbon contamination.

Vapor transport epitaxy, a novel growth technique for compound semiconductors

An advanced vapor transport epitaxy (VTE) technique for depositing compound semiconductors is described. The technique operates in the 10−1–10−6 Torr range using elemental, gas, or metalorganic sources. We have previously demonstrated elemental VTE oval defect‐free growth of several microns of GaAs at growth rates exceeding one micron per hour, on GaAs (100) and (111) 2° off toward 〈110〉 substrates. Elemental VTE is reviewed, and the effects of hydrogen on elemental VTE are discussed. The deposition process for GaAs films using metalorganic sources is described and results are presented. Electrical characteristics, as measured by Hall and sheet resistivity, show that films deposited using monoethylarsine and triethylgallium are n type as deposited. The resolving of several problems common to molecular‐beam epitaxy, chemical‐beam epitaxy, and metalorganic chemical vapor deposition systems has been the motivation for investigation of this technique.

Uniformity Control in Elemental Vapor Transport Epitaxy

Elemental Vapor Transport Epitaxy (EVTE) is a novel technique for semiconductor manufacturing, which combines the advantages of Molecular Beam Epitaxy (MBE) and Vapor Phase Epitaxy (VPE). EVTE provides a high level of elemental flux control, scaling to large deposition areas, and elimination of elemental Ga source related oval defects. EVTE has been successfully applied to the deposition of III-V and II-VI thin films and heterostructures. Design considerations and evaluations of the novel EVTE elements: elemental flux regulating valve operating at temperatures >1250°C with demonstrated response times less than 1 second and elemental flux distribution manifold are presented. The calculated operational parameters for EVTE are in good agreement with the observed experimental results.

Growth of MnS, Cd1-xMnxSe, and MnS1-xSex Films by Molecular Beam Epitaxy (MBE) and Elemental Vapor Transport Epitaxy (EVTE) Techniques

This work addressed the MBE and EVTE growth of wide band gap semiconductor materials such as MnSe, Cd 1-x Mn x Se, and MnS 1-x Se x which have potential application for blue-green light emitters. It is the first time that EVTE was applied for high (Se, S, Cd) and low (Mn) vapor pressure materials, which required modification of the conventional design. The films were grown on GaAs 2° off (100) substrates and characterized using optical microscopy, SEM, EDS, X-ray, SIMS, Hall, and sheet resistance measurements. The deposition process parameters will be reviewed and related to results such as film composition, surface morphology, uniformity, and crystallinity. We report on growth of Cd 1-x Mn x Se with 0.42 1 _ x Se x with 0.58

Vapor transport epitaxy: an advanced growth process for III-V and II-VI semiconductors

The Vapor Transport Epitaxy (VTE) thin film deposition technique for the deposition of III - V and II - VI compound semiconductors and material results are reviewed. The motivation for development of the VTE technique is the elimination of several problems common to molecular beam epitaxy/chemical beam epitaxy and metalorganic chemical vapor deposition systems. In VTE, vapors from sources feed through throttling valves into a common manifold which is located directly below the inverted wafer. A high degree of film uniformity is achieved by controlling the flux distribution from the common manifold. The technique operates in the 10-4 - 10-6 Torr range using elemental, metalorganic or gaseous precursors. The system is configurated for 2 inch diameter wafers but the geometry may easily be scaled for larger diameters. Using elemental sources, we have demonstrated oval defect free growth of GaAs on GaAs (100) and (111) 2 degree(s) off substrates, through several microns of thickness at growth rates up to ten microns per hour. GaAs films which were grown without the manifold exhibit classic oval defects. The deposition rate of ZnSe films as a function of elemental flux, VI/II ratio, and growth temperature are described. The ZnSe films exhibited smooth surface morphologies on GaAs (100) 2 degree(s) off substrates. X- ray analysis shows that III - V and II - VI films exhibited crystallinities comparable to films produced by molecular beam epitaxy and metalorganic chemical vapor deposition techniques.