Ar Ambient Research Articles

Comparison of Electrical, Optical, and Structural Properties of RF-Sputtered ZnO Thin Films Deposited Under Different Gas Ambients

Transparent conducting ZnO:Al thin films were prepared by rf-magnetron sputtering under different gas ambients at 300 °C. The electrical resistivity varied from 1.23×10-1 to 2.8×10-4 Ω cm introducing O2 and H2 gas with Ar ambient. The minimum sheet resistance of ZnO:Al film is 3.5 Ω/square. The maximum carrier concentration and Hall mobility as estimated from Hall effect measurement of the films were 2.3×1021/cm3 and 44.4 cm2 V-1 s-1 respectively. Photoluminescence (PL) spectra peaks are mainly in the blue emission region and change from 432 nm (2.87 eV) and 541.5 nm (2.29 eV) with the change of gas ambients. From the X-ray diffraction (XRD) pattern exhibiting only the <002> peak of ZnO, all films were found to be c-axis-oriented. The crystallite size varies from 150 to 288 Å for different films calculated from <002> orientation of XRD data. The characteristic features of ZnO films prepared under Ar+H2 ambient are their high carrier concentration, high strain values, high band gap and blue emission compared to the other ZnO films. The structural, electrical, optical properties and surface topography of ZnO thin films using XRD, Hall measurements, PL, UV–visible (vis)–near IR (NIR) spectroscopy and atomic force microscopy (AFM) have been investigated.

Surface plasmon enhanced ultraviolet emission from ZnO films deposited on Ag∕Si(001) by magnetron sputtering

The ZnO films were grown on Ag∕Si(001) substrates by sputtering Ag and ZnO targets successively in a pure Ar ambient. A significant enhancement of ZnO ultraviolet emission and a reduction of its full width of half maximum have been observed while introducing a 100nm Ag interlayer between ZnO film and Si substrate. Furthermore, a complete suppression of the defect related visible emission was also found for the ZnO∕Ag∕Si sample. This improved optical performance of ZnO is attributed to the resonant coupling between Ag surface plasmon and ultraviolet emission of ZnO.

Oxygen precipitate denuded zone formation in Czochralski silicon wafer based on rapid thermal processing in nitrogen ambient

The effects of temperature and cooling rate of the rapid thermal processing (RTP) in N2 ambient on oxygen precipitation and the formation of denuded zone (DZ) in Czochralski (CZ) silicon subjected to a subsequent low–high (L–H) two-step annealing have been investigated. It is found that as long as the cooling process of the RTP in N2 ambient is sufficiently slow, the DZ can be definitely formed. Moreover, it is revealed that, with respect to the RTP in Ar ambient, the RTP in N2 ambient can be carried out at lower temperatures to achieve the comparable oxygen precipitation in the subsequent L–H two-step annealing, indicating that the internal gettering (IG) process for CZ silicon wafers can be based on the RTP in N2 ambient at lower temperatures.

Growth and Properties of Stannite-Quaternary Cu&lt;sub&gt;2&lt;/sub&gt;ZnSnSe&lt;sub&gt;4&lt;/sub&gt; Thin Films Prepared by Selenization of Sputtered Binary Compound Precursors

Cu2ZnSnSe4 (CZTSe) thin films were grown on Corning glass 1737 by sequential methods of sputtering deposition and selenization process. As-grown films showed that elemental Cu, Zn, and Sn were in the nearly CZTSe stoichiometric ratio with Se-deficiency as detected by Energy Dispersive X-Ray spectrometry (EDX). In order to attain film stoichiometry, as-deposited films were subjected to selenization process in tube furnace under Ar ambient at different selenization temperatures for 10-60 min. It was found that compositions of binary compound in the sputtering target as well as selenization are critical for the growth of the CZTSe films. The structural characteristics of the selenized CZTSe films revealed a highly oriented stannite CZTSe phase with (112), (220/204) and (312/116) growth orientations and a CuSe secondary phase. By using 0.5% KCN solution, CuSe secondary phase could be totally etched from the CZTSe film surface.

Enhancement of photoelectrochemical response by aligned nanorods in ZnO thin films

ZnO thin films are deposited in pure Ar and mixed Ar and N 2 gas ambient at various substrate temperatures by rf sputtering ZnO targets. We find that the deposition in pure Ar ambient leads to polycrystalline ZnO thin films. However, the presence of N 2 in the deposition ambient promotes the formation of aligned nanorods at temperatures above 300 °C. ZnO films with aligned nanorods deposited at 500 °C exhibit significantly enhanced photoelectrochemical response, compared to polycrystalline ZnO thin films grown at the same temperature. Our results suggest that aligned nanostructures may offer potential advantages for improving the efficiency of photoelectrochemical water-splitting for H 2 production.

Electrical and optical properties of epitaxial transparent conductive BaCuTeF thin films deposited by pulsed laser deposition

Transparent p-type conductive BaCuTeF thin films are reported. Epitaxial BaCuTeF films are obtained in situ by pulsed laser deposition in ultra-high vacuum and in Ar ambient up to 1 × 10 −3 Torr on single-crystal MgO (100) substrates above 500 °C. Nominally undoped films exhibit hole carrier mobilities of 4–8 cm 2/V s with a maximum conductivity of 167 S/cm. Polycrystalline films deposited under similar conditions on amorphous SiO 2 substrates have hole mobilities of 0.2 cm 2/V s and conductivities of 0.4–7 S/cm. The largest change in optical absorption occurs near 3 eV, with a weak feature near 2.4 eV in epitaxial films.

ANNEALING TEMPERATURE EFFECT ON THE FIELD EMISSION PROPERTIES OF CARBON NANOTUBE FILMS

As the carbon nanotubes (CNTs) films are applied to the field emission cathodes in the vacuum devices, heat treatment in the range of 400°C–500°C is often conducted during the device sealing process, especially for glass-based devices. The annealing temperature effect on the field emission of the CNT films prepared by chemical vapor deposition is investigated. The CNT film annealed at 400°C in air contains less amorphous carbon phase, and shows better field emission properties comparing to the as-grown CNT film. Annealing at 450°C causes serious oxidative damage along the tube walls, resulting in the poor field emission performance. The CNTs annealed at 500°C are all burned out. The experiment shows that the sealing temperature at 400°C or below can be conducted in air, while the sealing temperature above 400°C should be done in N 2 or Ar ambient.

Use of Graphite Cap to Reduce Unwanted Post-Implantation Annealing Effects in SiC

6H and 4H–SiC epilayers were Al-implanted at room temperature with multiple energies (ranging from 25 to 300 keV) in order to form p-type layers with an Al plateau concentration of 4.5×1019 cm-3 and 9×1019 cm-3. Post-implantation annealing were performed at 1700 or 1800 °C up to 30 min in Ar ambient. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. From Atomic Force Microscope measurements, the roughness is found to increase drastically with annealing temperature for unprotected samples while the C capped samples show a preservation of their surface states even for the highest annealing temperature. After 1800°C/30 min annealing, the RMS roughness is 0.46 nm for the lower fluence implanted samples, slightly higher than for unimplanted samples (0.31 nm). Secondary Ion Mass Spectroscopy measurements confirm that the C cap was totally removed from the SiC surface. The total Al-implanted fluence is preserved during postimplantation annealing. A redistribution of the Al dopants is observed at the surface which might be attributed to Si vacancy-enhanced diffusion. An accumulation peak is also observed after annealing at 0.29 9m, depth corresponding to the amorphous/crystalline interface that was determined on the as-implanted samples by Rutherford Backscattering Spectroscopy in channeling mode. The redistribution of the dopants has an impact on their electrical activation. A lower sheet resistance (Rsh= 8 k) is obtained for samples annealed without capping than for samples annealed with C capping (Rsh= 15 k ).

Borides of Ag and Au prepared by magnetron sputtering

Following the discovery of MgB 2 that has a superconductive critical temperature ( T c) of ∼39 K much research was initiated in the search for materials with higher T c. Theoretical studies predicted that diborides of metals having the AlB 2 type structure, among them AgB 2 and AuB 2, may be superconductive at values of T c even higher than 39 K. In our attempts to prepare AgB 2 and AuB 2 using films of the Ag–B and Au–B systems, no superconductivity was observed. Equilibrium phase diagrams of these systems do not support the possibility of forming AgB 2 or AuB 2 compounds, despite a report which indicates their existence. Films of the Ag–B and Au–B systems were obtained by magnetron cosputtering from two separate targets, that of B and Ag (or Au) on Si(1 0 0) substrates in Ar ambient. The specimens were subjected to X-ray diffraction (XRD), secondary electron microscopy (SEM), X-ray photo spectroscopy (XPS), Auger analysis and optical microscope (OM) investigations. No superconductivity was observed in the range 10–200 K on the basis of resistivity measurements. The films were not homogeneous, but rather the alloys had decomposed into two separate phases. One of the phases was in the form of dispersed particles. An XRD peak at 28° was observed which supposedly is characteristic of a noble metal boride. The possibility that the XRD peaks might belong to a boric acid phase also exists. The boric acid phase had the same diffraction peak as was observed by XRD in our films.

Effects of two‐step rapid thermal processing in different ambients on denuded zone and oxygen precipitation in Czochralski silicon

AbstractThe effects of two‐step rapid thermal processing (RTP) sequentially in different ambients on the formation of denuded zone (DZ) and oxygen precipitation in the Czochralski (CZ) silicon wafers have been investigated. With the first‐step RTP in Ar ambient, no obvious DZ but a high density of bulk micro‐defects (BMDs) were formed in the sample with the second‐step RTP in N2 ambient, while the BMD density in the sample with the second‐step RTP in O2 ambient was remarkably low. With the first‐step RTP in N2 ambient, a high density of BMDs and a width of DZ could be formed in either of the samples with the second‐step RTP in Ar or O2 ambient, but the DZ width in the two samples differed to a certain extent. With the first‐step RTP in O2 ambient, the two samples with the second‐step RTP in Ar and N2 ambients respectively possessed reasonably comparable DZ width and BMD density. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electron spin resonance from annealed titania nanotubes

Titania nanotubes were prepared using a hydrothermal method. Hydrogen titanate nanotubes (H-TNTs) with an anatase phase changed to anatase nanocrystals at about 500 °C, and then a rutile structure at ∼800 °C. A sharp and symmetrical electron spin resonance (ESR) signal (g=2.003), attributed to a single-electron-trapped oxygen-vacancy (SETOV), was obtained at the annealed H-TNTs (T<500 °C). The SETOV signal increased and maximized remarkably at about 400–500 °C. Then, the nanotube structure appeared to be demolished. Yet, when the vacuum-heated H-TNTs were sealed in N2 or Ar ambient, some additional ESR signals appeared besides the SETOV signal. The broad asymmetric ESR signal (g=1.98) was attributed to a surface oxygen vacancy related to the Ti3+ sites in a reduced TiO2 matrix. The vacuum-heated sodium titanate nanotubes (Na-TNTs) showed only the SETOV signal (T<500 °C).

Effects of annealing on the electrical and interfacial properties of amorphous lanthanum scandate high-κ films prepared by molecular beam deposition

Amorphous LaScO3 thin films were grown on (100) Si by molecular beam deposition and the effects of postdeposition thermal treatments on the film properties were studied after anneals in O2 or inert Ar atmosphere at 400 or 650 °C. Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS) were employed to investigate the samples. Capacitance-voltage and current-voltage measurements allowed their electrical characterization. Postdeposition annealing in O2 reduces hysteresis, flatband voltage, and also leakage current density. In contrast, films treated in Ar ambient revealed a different behavior. The observations were associated with the interface evolution as studied by XPS, which verify that an O2 atmosphere favors the formation of a SiO2-rich interface between the film and the Si substrate, while a La-Sc-silicate-like compound predominates in this region after treating the samples in Ar. Additionally, postdeposition annealing results in an improvement of the dielectric constant up to 33, which is higher than that previously determined for LaScO3 or other amorphous alternative high-κ oxide films deposited by various techniques.

Fabrication of CeO2 Dielectric Films by Chemical Vapor Deposition with a Liquid Metal Organic Source

Cerium dioxide films were deposited by chemical vapor deposition using tetrakis (3-methyl-3-pentoxy) cerium. In the present CVD process, Arrhenius plots indicated the existence of two activation energies of 0.85 eV and 0.29 eV. For the samples deposited under the condition of the lower activation energy of 0.29 eV, electrical properties were improved after annealing at 500 {degree sign}C in Ar, O2, and O-radical ambient. A hysteresis of 2.0 V and a flat band voltage shift of 3.0 V for the as-deposited film decreased to 0.15 V and almost 0 V after annealing, respectively. The leakage current decreased by 4 orders of magnitude after annealing in an oxidizing ambient, and even more improved value of the order of 10-7 A/cm2 was obtained after annealing in the O-radical ambient. For the samples deposited under the condition of the higher activation energy of 0.85 eV, however, electrical properties were not improved even after annealing.

Photoluminescence from Magnetron Sputtered SiO2 Films Co-doped with (Er, Ge) under Excitation of a 325 nm He-Cd Laser Line

We have studied photoluminescence (PL) from SiO2 films co- doped with (Er, Ge) deposited by magnetron sputtering of an Er+Ge+SiO2 composite target in pure Ar ambient. Under excitation of a 325 nm He-Cd laser line, blue emission bands around 400 nm and near infrared bands around 800 nm have been observed, which are attributed to Ge-related defects and Ge nanoclusters (Ge-ncls), respectively. Strong Er3+ PL at 1.54 μm was also observed from the films, while the Er PL intensity of a control Er-doped SiO2 film (i.e., without Ge), is negligible under the same excitation. All the PL intensities vary as functions of thermal annealing temperatures. The results demonstrate that the significant enhancement of Er PL in the (Er, Ge) co-doped SiO2 films are due to the incorporation of Ge. The roles of Ge-ncls and Ge-related defects to the Er3+ excitation are discussed.

250 °C operation normally-off GaN MOSFETs

We tried normally-off operation GaN metal–oxide–semiconductor field effect transistors (MOSFETs). n+ Contact layers as a source and drain region were fabricated using a Si ion implantation technique with the activation annealing at 1300 °C for 30 s in Ar ambient. The ohmic contact and sheet resistance of n+ contact layer were 1.1 × 10 −7 Ω cm 2 and 53 Ω/sq, respectively. As a result, we achieved a normally-off operation GaN MOSFETs and moreover high temperature operation of 250 °C for the first time. Threshold voltage ( V th) was +3 V. Drain current ( I d) was over 100 mA/mm at gate voltage ( V g) of 10 V and drain-to-source voltage ( V ds) of 10 V. Maximum field effect mobility ( μ FE) was 210 cm 2/V s at V ds = 0.1 V.

Dependence of conduction type of ZnO films prepared by sputtering a Zn 3As 2/ZnO target on substrate temperature and thermal treatment

ZnO films were deposited on glass substrates by sputtering a Zn 3As 2/ZnO target using radio frequency (rf) magnetron sputtering. XRD was used to analyze the crystal orientation of ZnO films. Energy dispersive spectroscopy result shows that As content in ZnO:As films is nearly uniform. Room temperature Hall and resistivity measurements indicate that the substrate temperature is an important factor to determine conduction type of ZnO films and proper thermal treatment for the films may change their electrical behavior from n type to p-type. As-doped ZnO film shows p type conductivity with mobility as high as 4.07 cm 2/V s after annealing in Ar ambient at 400 °C for 60 min.

Effects of Illumination on Ar+-Implanted n-Type 6H-SiC Epitaxial Layers

Argon ions were implanted into n-type 6H-SiC epitaxial layers at 600°C. Postimplantation annealing was carried out at 1,600°C for 5 min in an Ar ambient. Four implantation-induced defect levels were observed at EC-0.28 eV, EC-0.34 eV, EC-0.46 eV, and EC-0.62 eV by deep level transient spectroscopy. The defect center at EC-0.28 eV is correlated with ED1/ED2 and with ID5. The defect at EC-0.46 eV with a capture cross section of 7.8 × 10−16 cm2 is correlated with E1/E2, while the defect at EC-0.62 eV with a capture cross section of 2.6 × 10−14 cm2 is correlated with Z1/Z2. Photo deep level transient spectroscopy was also used to study these defects. Upon illumination, the amplitudes of the deep level transient spectroscopy (DLTS) peaks increased considerably. Two emission components of Z1/Z2 were revealed: one fast and the other slow. The fast component could only be observed with a narrow rate window. In addition, a new defect was observed on the low-temperature side of the defect at EC-0.28 eV when the sample was illuminated.

Size control of catalytic nanoparticles by thermal treatment and its application to diameter control of single-walled carbon nanotubes

The authors report size control of catalytic nanoparticles by thermal annealing for diameter-controlled growth of single-walled carbon nanotubes (SWNTs). They found that Co nanoparticle-size gradually decreased through repetitive annealing at 1000°C in Ar ambient. Results of x-ray photoelectron spectroscopy and secondary ion mass spectroscopy show that thermal evaporation is responsible for the decrease. After SWNT growth using this phenomenon, the authors found that thinner SWNTs with a narrower diameter distribution grew as the nanoparticles became smaller. Their results provide a rational and straightforward technique to prepare catalysts having a desirable size and uniformity toward diameter-controlled SWNT growth.

Transparent, Low Resistance, and Flexible Amorphous ZnO-Doped In2O3 Anode Grown on a PES Substrate

Transparent and low resistance amorphous ZnO-doped (IZO) anode films were grown by radio-frequency (rf) sputtering on an organic passivated polyethersulfone (PES) substrate for use in flexible organic light-emitting diodes (OLEDs). Under optimized growth conditions, a sheet resistance of , average transmittance above 89% in the green range, and a root mean square roughness of were obtained, even for the IZO anode film grown in a pure Ar ambient without the addition of oxygen as a reactive gas. All of the IZO anode films had an amorphous structure regardless of the rf power and the working pressure due to the low substrate temperature of and the structural stability of the amorphous IZO films. In addition, an X-ray photoelectron spectroscopy depth profile obtained for the IZO/PES showed no obvious evidence of interfacial reactions between the IZO anode and the PES substrate, except for some indiffusion of oxygen atoms from the IZO anode. Furthermore, the current-voltage-luminance of the flexible OLEDs fabricated on IZO anode was found to be critically dependent on the sheet resistance of the IZO anode.

Effect of annealing temperature and ambient gas on phosphorus doped p-type ZnO

The authors report on the thermal activation of phosphorus doped p-type ZnO thin films grown by radio frequency magnetron sputtering. The p-type ZnO was produced by activating phosphorus doped ZnO thin films in N2, Ar, or O2 ambients. The hole concentration of the p-type ZnO, prepared in an O2 ambient, showed a lower hole concentration compared to samples annealed in N2 and Ar ambients. The activation energies of the phosphorus dopant in the p-type ZnO under different ambient gases indicate that phosphorus atoms replace oxygen atoms in the ZnO to form PO which acts as an acceptor.