Organic Vapor Phase Deposition Research Articles

Preparation of 8-hydroxyquinoline wires by decomposition of tris(8-hydroxyquinoline) aluminium

We fabricated 8-hydroxyquinoline (HQ) wires by two methods, decomposition of tris(HQ) aluminium at low pressure in a tube furnace and heating of HQ powder at atmospheric pressure. Fabricated wires were crystalline, and exhibited the same optical properties (absorption and photoluminescence) as HQ powder. While the properties of wires prepared by two different methods were the same, it should be noted that synthesis by decomposition of tris(HQ) aluminium required elimination of mechanical vibration of the growth tube. Implications of decomposition of tris(HQ) aluminium during organic vapour phase deposition growth on organic optoelectronic device performance are discussed.

GaN BASED 3D CORE-SHELL LEDS

As a promising novel route towards highly efficient optoelectronic devices, GaN based 3D core-shell light emitting diodes (LEDs) have attracted increased attention in recent years. In comparison to conventional 2D thin film LED, the 3D LED systems using a core-shell geometry with high aspect ratio are a breakthrough in technology with lots of advantages. In this paper, we review our developed growth strategies of these LED systems on Si and sapphire substrates. A catalyst free selective area growth of GaN 3D core-shell LED systems was realized using patterned substrates by metal organic vapor phase deposition in a convenient continuous-flux growth mode. We have recently suggested that the surface polarity plays a crucial role for the morphology of GaN 3D structure growth. In order to analyze the surface polarity of 3D submicron or micron structures, Kelvin probe force microscopy and selective etching techniques have been developed. During the growth of GaN submicron rods and micron columns on patterned SiOx /sapphire templates, mixed polarity effects could be detected. A new "truncated pyramid + column" growth method was developed to effectively avoid the formation of mixed polarity and realize single N-polar GaN 3D devices. Transmission electron microscopy and spatially and spectrally resolved cathodoluminescence measurements evidently prove the core-shell structure of 3D LED systems.

P-Type Doping of Small-Molecule Organic Semiconductors using Organic Vapor Phase Deposition (OVPD)

ABSTRACTIn the past few years, organic vapor phase deposition (OVPD) has been demonstrated to be an effective deposition method for high-performance monochrome and white organic light emitting diodes (OLEDs) [1-4]. OVPD provides good material utilization efficiency and large achievable deposition rates.An application of p-type doping is the improvement of hole injection either from the anode contact or from a charge generation layer in stacked OLEDs [5]. Nevertheless, no reports on p-type doping using OVPD can be found in literature, in part due to the thermal instability and high chemical sensitivity of organic dopants.In this work, p-type doping using an AIXTRON Gen-1 OVPD tool with two different show-erhead designs is examined. NDP-2 (NOVALED) and N,N‘-diphenyl-N,N‘-bis(1-naphthylphenyl)-1,1‘-biphenyl-4,4‘-diamine (NPB) were used as p-type dopant (guest) and hole-conducting host, respectively. p-Type doped hole-only devices were fabricated and compared with undoped ones.Two different showerhead designs (made either of aluminum or stainless steel) were investi-gated with respect to OLED performance to determine possible side reactions.Highly efficient monochrome red OLEDs including a p-type doped hole transport layer were demonstrated exhibiting a current efficiency of 31 cd/A, a power efficiency of 26 lm/W and a driving voltage of 3.7 V without improved light outcoupling (all values at 1000 cd/m2).

Influence of OVPD parameters on the performance of organic solar cells utilizing pentacene/PTCDI absorption layers

ABSTRACTAs global energy demand is steadily growing, renewable energy generation by solar cells is becoming increasingly important. The use of mono- and polycrystalline silicon solar cells, which nowadays dominate the market, is limited by wafer size, rigidness of substrates and the requirement of large energy amounts for manufacturing. Organic solar cells (OSC) have the potential to overcome these limitations; especially organic vapor phase deposition (OVPD) technology offers the possibility of reproducible, large-scale production at low temperatures and on flexible substrates.We report on planar heterojunction OSC utilizing an active layer of pentacene/N, N’- ditridecylperylene-3, 4, 9, 10-tetracarboxylic diimide (PTCDI) fabricated by an Aixtron Gen-1 OVPD tool. The influence of substrate temperature was studied using atomic force microscopy (AFM) on single layers and bilayers. In addition electrical characterization with and without illumination of fully processed solar cells which utilize different cathode layers was carried out.AFM images indicate that crystallization of pentacene layers can be widely influenced by substrate temperature, a PTCDI-C13H27 layer atop of these covers the crystallites. Open-circuit voltage was found to be 0.47 V and short-circuit current densities beyond 0.8 mA/cm2 were measured under a spectrum close to AM 1.5 with 100 mW/cm2. Fill factors were determined to be as high as 44 %.

Highly Efficient OVPD-Processed Resonant-Cavity OLED Comprising a Semitransparent Ag layer

ABSTRACTThe light out-coupling potential of introducing a semitransparent Ag layer between the anode and the organic layer stack of monochrome bottom-emitting organic light emitting diodes (OLED) is examined. Red and green phosphorescent as well as deep-blue fluorescent resonant-cavity OLED (RC-OLED) comprising a semitransparent Ag layer are processed by means of organic vapor phase deposition (OVPD). An enhancement of the luminous efficiency of up to 81% can be observed.The impressive efficiency enhancement can be explained by a reduced formation of substrate modes in combination with a strong narrowing of the emission spectrum leading to an increased true luminous efficiency.

38.1: Invited Paper: Enabling High Throughput OLED Manufacturing by Carrier Gas Enhanced Organic Vapor Deposition (OVPD)

AbstractThis paper describes a new Organic Vapor Phase Deposition source characterized by substantially reduced vaporization temperatures and extremely short thermal exposure time of the organic material. A vapor flux of 3 mg/s is practical while maintaining thickness non‐uniformity under 2% and deposition efficiency of 70% at the Gen 4 scale.

Ordered organic-organic multilayer growth

Crystalline order and orientation influence both the electronic and optical properties of thin organic crystalline films. Here, we demonstrate the quasiepitaxially ordered growth via organic vapor phase deposition of two organic materials, 1,4,5,8-naphthalene-tetracarboxylic-dianhydride and dibenzotetrathiafulvalene-tetracyanoquinodimethane on single-crystal substrates. To understand the quasiepitaxial orientations between the organic-inorganic and organic-organic lattices we compare geometrical lattice registry to full-structure van der Waals potential calculations, and find that only the complete description of the atomistic potential correctly matches experimentally observed orientations. We also demonstrate single-crystalline film growth of alternating multiple quasiepitaxial layers of these two organic semiconductors, and discuss this phenomenon in the context of incommensurate quasiepitaxy and surface energy matching, which is distinct from the lattice-matching criterion for inorganic heteroepitaxy.

Hybrid white organic light-emitting diode with a mixed-host interlayer processed by organic vapor phase deposition

Abstract. Organic light-emitting diodes (OLEDs) are a key technology in solid state lighting.Withoutalong-livedphosphorescentblueemitter,ahybridconceptbasedonphosphorescentredandgreenemittersandafluorescentblueemitterinawhiteOLEDstackisapromisingapproachfor pure-white emission. Several challenges such as exciton recombination on all emitters andtripletdiffusion,aswellasquenching,havetobeovercome.Toaddresstheseissues,amixed-hostphosphorescent emission layer is employed. The mixture ratio is locally varied in the emissionlayer. An interlayer separates the phosphorescent and fluorescent emission layer. Strategies totune the color coordinates are presented. The lifetime and color stability versus luminance areinvestigated. At Commission Internationale de I’Eclairage color coordinates of 0.44/0.44, acurrent efficacy of 28.0 cd/A (at 1000 cd/m 2 ), and a luminous efficacy of 20.6 lm/W can bemeasured. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE) . [DOI: 10.1117/1.3545966]

Optical properties of organic thin films deposited via organic vapour phase deposition

AbstractIn recent years, organic semiconductors attracted a lot of attention due to their potential use in organic electronics such as light emitting diodes (OLEDs), photovoltaics and photodetectors. Tris‐(8‐hydroxyquinoline)‐aluminium(III) (Alq3) and N,N_‐di‐[(1‐naphthyl)‐N,N‐diphenyl]‐(1,1‐biphenyl)‐4,4‐diamine (α‐NPD) are among the most commonly used electron transport and hole‐transport materials in OLEDs, respectively. In this work, Alq3 and α‐NPD thin films with various thickness values were deposited onto Si and glass substrates by organic vapour phase deposition (OVPD). Spectroscopic Ellipsometry (SE) in a wide spectral region from the infrared (IR) (900–4000 cm−1) to the near infrared–visible–far ultraviolet (NIR–Vis–fUV, 0.7–6.5 eV) has been implemented in order to investigate the influence of the thickness on their optical and structural properties. From the analysis of the SE spectra, we estimated the band gap values, the optical absorptions and the vibrational response of the materials. The results showed that the α‐NPD thin films show four characteristic absorptions and the optical response of the material is independent of the films thickness. Finally, in case of Alq3, the material shows a band gap at 2.7 eV and three characteristic absorptions.

Characterization of amorphous organic thin films, determination of precise model for spectroscopic ellipsometry measurements

The optical properties of tris(8-hydroxyquinoline) aluminum (Alq 3), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD) and other amorphous organic materials for OLEDs application, e.g. 4,4-bis(2,2-diphenyl vinyl)-1,1-biphenyl (DPVBI) and Spiro-DPVBI have been studied by multi-angle spectroscopic ellipsometry (SE). The thin films of these materials have been deposited by organic vapor phase deposition (OVPD). The structural characterization has been performed using atomic force microscopy (AFM) and X-ray reflectometry (XRR). Comparison of the measurements using these different independent techniques enables the precise determination of the optical model for dielectric function of these thin films. The detail analyses on Alq 3 and α-NPD show that the Kim model with Gaussian broadening provides a significantly better fit to the ellipsometry data than the frequently used harmonic oscillator model. This conclusion is further proved by performing similar measurements on other amorphous organic samples for OLEDs application, e.g. DPVBI and Spiro-DPVBI. This result can be explained by the characteristic features of electronic states in organic molecules.

A Growth and Morphology Study of Organic Vapor Phase Deposited Perylene Diimide Thin Films for Transistor Applications

In this work, an in-depth growth study with organic vapor phase deposition of the n-type semiconductor N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) is presented. The organic vapor phase deposition technique allows independent control of more parameters than traditional vapor thermal evaporation, namely, not only deposition flux and substrate temperature but also chamber pressure can be changed. We study the influence of these parameters on the morphology and microstructure of PTCDI-C13 thin films, and correlate them with electrical properties. Films of PTCDI-C13 on SiO2 surfaces modified with poly-(α-methylstyrene) exhibit Stranski−Krastanov growth. Upon increasing deposition flux, the resulting surface morphology changes from rough films, characterized by needle growth, to smoother films consisting of small, uniform grains. Notably, increasing the pressure shifts this morphology transition toward lower deposition fluxes. All X-ray reflectivity measurements are indicative of PTCDI-...

Organic vapor phase deposition for the growth of large area organic electronic devices

We demonstrate that material utilization efficiencies of 50% and deposition nonuniformities ≤2.5% are achievable over substrate diameters of 200 mm using a simplified, organic vapor phase deposition (OVPD) system. The OVPD system is used to demonstrate doped electrophosphorescent organic light emitting diodes whose performance is comparable to those grown by vacuum thermal evaporation. Through continuum modeling, we demonstrate that analogous systems whose chamber dimensions are comparable to the substrate width are scalable to substrate sizes of at least 1500×1800 mm2 with deposition nonuniformities between 1.5% and 2.5%. These results indicate that OVPD is useful in the large area deposition of displays, lighting, and other organic electronic devices.

Investigation of Oxygen Vacancies in Micro-Patterned PZT Thin Films Using Raman Spectroscopy

Micro-patterned Pb(Zr,Ti)O3 (PZT) films with dot-pattern were grown by metal organic chemical vapor phase deposition (MOCVD). Micro-patterned Pb(Zr,Ti)O3 (PZT) films were formed on dot-patterned SrRuO3 (SRO) buffer layer that was prepared by MOCVD through the metal mask on (111)Pt/Ti/SiO2/Si substrate. The orientation of dot-patterned PZT films was ascertained by the micro-beam x-ray diffraction (XRD) and their crystallinity was characterized by Raman spectroscopy. It was found that PZT films were oriented to (111) on dot-pattern, while (100)/(001) out of dot-pattern and the amount of oxygen vacancies at the circumference of the dot-pattern were larger than that of center of dot-pattern.

Growth of pentacene thin films by in-line organic vapor phase deposition

We present the extension of the organic vapor phase deposition technique to an in-line geometry, in which the sample travels underneath an elongated showerhead that sprays molecules transported by a stream of carrier gas. Highly uniform pentacene films are grown at web speeds of up to 2.1 m/min, equivalent to an average deposition rate of 105 Å/s in a static system. With transistor mobilities of up to 1.5 cm 2/V s, these pentacene films are of high electrical quality. Importantly, this quality is conserved up to the highest deposition speeds. We discuss the relationships between in-line deposition rate, morphology and crystallinity of the deposited pentacene films and their electrical characteristics.

Orientation controlled deposition of Pb(Zr,Ti)O3 films using a micron-size patterned SrRuO3 buffer layer

Orientation controlled, micron-sized dot-patterned PZT films were grown by metal organic chemical vapor phase deposition (MOCVD), and their crystal structure was evaluated. A micron-size dot-patterned SrRuO3 (SRO) buffer layer was initially prepared by MOCVD through a metal mask on the (111) Pt/Ti/SiO2/Si substrate. Then, a PZT film was deposited over the entire substrate. Micron-beam X-ray diffraction and Raman spectroscopy indicated that (111)-orientated PZT was prepared on the SRO covered area, while the (100)/(001)-orientated one was directly grown on Pt-covered substrates. The PZT film grown on SRO was thinner than that on the Pt-covered substrate. The estimated ferroelectric property on the center of the dot pattern was larger than that at the circumference by Raman spectroscopy because the strain is accelerated at the center of the dot.

When Fewer Photons Do More: A Comparative O2Photoadsorption Study on Vapor-Deposited TiO2and ZrO2Nanocrystal Ensembles

The charge separation properties of TiO2 and ZrO2 nanocrystal powders which were produced by metal organic chemical vapor phase deposition were compared by means of O2 photoadsorption. Prior to the UV excitation experiments, we carefully explored the structure and morphology as well as the spectroscopic properties of the dehydroxylated nanoparticles in controlled gas atmospheres using UV diffuse reflectance, FT-IR, and electron paramagnetic resonance spectroscopy. On the basis of this information, we utilized the photogeneration of surface-adsorbed O2− radicals and their detection by EPR spectroscopy to quantify the concentration of separated charges and to relate these figures to the number of oxide particles that were exposed to known numbers of UV photons with defined energies. The results presented in this study reveal that upon band-gap excitation, ZrO2 nanoparticles are by 2 orders of magnitude more efficient in oxygen-assisted charge separation than TiO2. The dramatically diminished charge separation yield in TiO2 is attributed to the existence of deep trap states which persistently stabilize paramagnetic holes and at the same time act as recombination centers. Their absence in ZrO2 nanocrystals gives rise to a comparable performance in terms of photoadsorbed O2 and essentially compensates for the significantly wider optical band gap in relation to TiO2.

MOCVD를 이용한 BiSbTe3박막성장 및 열전소자 제작

Bismuth-antimony-telluride based thermoelectric thin film materials were prepared by metal organic vapor phase deposition using trimethylbismuth, triethylantimony and diisopropyltelluride as metal organic sources. A planar type thermoelectric device has been fabricated using p-type and n-type thin films. Firstly, the p-type thermoelectric element was patterned after growth of thickness of layer. Again n-type film was grown onto the patterned p-type thermoelectric film and n-type strips are formed by using selective chemical etchant for . The top electrical connector was formed by thermally deposited metal film. The generator consists of 20 pairs of p- and n-type legs. We demonstrate complex structures of different conduction types of thermoelectric element on same substrate by two separate runs of MOCVD with etch-stop layer and selective etchant for n-type thermoelectric material. Device performance was evaluated on a number of thermoelectric devices. To demonstrate power generation, one side of the device was heated by heating block and the voltage output was measured. The highest estimated power of 1.3 is obtained at the temperature difference of 45 K.

OVPD®technology

The precise control of organic thin film processing by organic vapor phase deposition (OVPD®) is presented and analyzed on device level. OVPD® offers accurate and individual control of deposition layer properties like mixing of several materials (co-deposition) and the control of various morphologies by a wide process parameter space given by, e.g. substrate temperature, deposition rate and pressure. The benefit of precise co-deposition is demonstrated by an OLED with a sensitive twofold-doped emissive layer and revealed a doping level of 0.26% for the red dopant with a std. dev. of 0.38%. The effect of the various morphologies is investigated by optimizing the efficiency of molecular organic solar cells consisting of copper phthalocyanine (CuPc) and C60. With defined process parameters efficiencies of up to 3.0% were demonstrated.

Fabrication of Bismuth Telluride-Based Alloy Thin Film Thermoelectric Devices Grown by Metal Organic Chemical Vapor Deposition

Bismuth-antimony-telluride based thin film materials were grown by metal organic vapor phase deposition (MOCVD). A planar-type thermoelectric device was fabricated with p-type Bi 0.4 Sb 1.6 Te 3 and n-type Bi 2 Te 3 thin films. The generator consisted of 20 pairs of p-type and n-type legs. We demonstrated complex structures of different conduction types of thermoelectric elements on the same substrate using two separate deposition runs of p-type and n-type thermoelectric materials. To demonstrate power generation, we heated one side of the sample with a heating block and measured the voltage output. An estimated power of 1.3 μW was obtained for the temperature difference of 45 K. We provide a promising procedure for fabricating thin film thermoelectric generators by using MOCVD grown thermoelectric materials that may have a nanostructure with high thermoelectric properties.

Hybrid White Organic Light Emitting Diodes (OLED) Processed by Organic Vapor Phase Deposition

AbstractWhite OLED consisting of a fluorescent blue emissive layer combined with a phosphorescent green and a phosphorescent red emissive layer were processed by means of Organic Vapor Phase Deposition (OVPD). Different concepts to tune the color coordinates of the device are discussed with respect to the luminous efficiency. Furthermore, the influence of device aging on the emitted spectrum is being investigated by means of spectrally resolved lifetime measurements.