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Molybdenum dichalcogenide films (MoX2, X=S, Se) were fabricated on 6-inch wafers by a breakthrough technique utilizing cracked small X-molecules. Uniformly deposited Mo-metal films were sulfurized or selenized by reactive chalcogen (Xa, a= 1- 2) small molecules, and MoX2 film was approximately 3 times thicker than the Mo metal precursor. The behavior of reaction chamber pressure according to the cracking temperature indicated that one large molecule could crack into 4 – 5 small particles in experimental condition used in this work. The formation of protrusions was also effectively inhibited to obtain MoX2 films of a device quality. First, I will explain how effectively large chalcogen molecules (normally X8) were cracked, and the cracking effect on the film quality. By controlling the cracking temperature separately, we could lower the growth temperature down to 400 oC or lower. The effect of cracking and X-source evaporation temperatures on the film quality will be also presented. The film quality was dependent on the deposition technique of Mo metal films. The films were characterized using x-ray photoelectron spectroscopy (XPS), Raman scattering, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Cross sectional high resolution TEM image, energy-dispersive x-ray spectroscopy, and angle-resolved XPS analysis of 6 nm-thick MoS2 sulfurized at 570 oC showed that the film has well-aligned layer-by-layer crystalline structure and the composition and chemical states were uniform through depth. Normally, layer-by-layer grown MoX2 films on very flat surfaces are studied for device applications as reported in earlier works. But, practical devices require the growth of semiconductor films on rough and/or patterned surfaces. Then, we studied the formation of a few nm-thick and a few tens nm-thick MoX2 films on rough surfaces, and found that the MoX2 films could be successfully grown on a very rough substrate (root mean square roughness = 38 nm) using the method introduced in this work. When MoX2 films were grown by chalcogenizing Mo, the crystalline orientation of MoX2 films depended on the thickness of Mo films. When the Mo film is thinner than 5 nm, we could obtain layer-by-layer structured, i.e., MoX2 films. We had reported the successful application of the horizontally grown MoX2 film to the field effect transistors in the previous work [1]. Contrarily, when the Mo film was 5 nm or thicker, the formed MoX2 films had vertically oriented crystalline structure. It is because the stress due to 3 times volume expansion should be released by changing the crystalline orientation from planar layer-by-layered to vertically oriented structures. In this work, we utilized the vertically oriented MoX2 films as an interlayer between the semiconductor layer and the electrode. By adopting the MoX2 interlayer in amorphous silicon (a-Si:H) thin film photovoltaic devices having the inverted structure, we could obtain greatly improved cell performances. In the substrate type photovoltaic cells, the shunt resistance increased from 10 kΩ (no MoSe2) to 18 kΩ (with MoSe2) and the open circuit voltage increased from 0.717 V to 0.785 V. The a-Si:H photovoltaic cell having 26 % visible light transmittance on a glass substrate showed the conversion efficiency of 7.7 % under blue light irradiation of 7 mW/cm2. In conclusion, the horizontally and vertically oriented MoX2 films of high crystallinity were formed by chalcogenizing Mo metal films using reactive cracked small X-molecules, and the use of MoX2 film as an interlayer greatly improved the performance of a-Si:H thin film photovoltaic devices. The growth method introduced in this work would be one of the most promising methods to obtain uniform and high quality metal dichalcogenide films on a large substrate. The most important advantage of this method is that it can be easily applied to other metal chalcogenide materials. [1] Jung, K. H.; Yun, S. J.; Choi, Y.; Cho, J. H.; Lim, J. W.; Chai, H.-J.; Cho, D.-H.; Chung, Y.-D.; Kim, G. Nanoscale 2018, 10, 15213-15221.

Amorphous SiGe:H (a-SiGe:H) single junction solar cells having light absorbing layers with different Ge profiles were fabricated to investigate the effects of the Ge composition profiles on the solar cell performance. The structures of a-SiGe:H layers were characterized by (a) a constant Ge composition (18%), (b) a stepwise Ge composition, (c) a gradually decreased Ge composition profile (18 ~ 0%), and (d) a complex Ge profile, respectively. The cell performances were compared on the bases of current density – voltage characteristics curves and external quantum efficiency. Among the samples, cell (c) with a gradually decreased Ge profile showed the best performance.

In this article, TixSi1-xO (TSO) thin film varistors were fabricated by plasma enhanced atomic layer deposition (PEALD) in order to lower the varistor voltage. For protecting electronic circuit against high abnormal voltage surges, varistors have been used as a protecting device. So far, most varistors (all commercial varistors) have been fabricated as bulk ceramics. However, as a development of very large scale integration (VLSI) electronics, transient surge suppression for low voltage electronic circuit is required. This protection function is possible due to the varistor nonlinear electrical property that is given by the relation I=K·V, being α the nonlinearity coefficient, V, the applied voltage, I the current and K a constant. The TSO films with 70 nm were grown by PEALD at 250 °C. The TTIP and TEOS were used as precursors. The formation of one cycle for the TSO film comprised of NTi subcycles of TiO2 and NSi subcycles of SiO2, which designates the cycle coordinates (NTi, NSi). TSO (1,2), (1,1), (2,1), (3,1) were fabricated, thus the Ti content were varied. Film thickness of all samples were 71, 66, 68 and 66 nm and refractive indices were 1.93, 2.03, 2.14, 2.21 for TSO (1,2), (1,1), (2,1) and (3,1), respectively. Therefore, optical thickness, namely a product of film thickness and refractive index, can be controlled by PEALD, which can be powerful technique. Figure 1 shows a vertical structure of metalvaristor-metal fabricated by sputter method and PEALD on glass substrate. Mo and ITO were used as top and bottom electrodes, respectively. In the measurement of current-voltage (I-V) characteristics, different curves were obtained, namely asymmetric curve, with both polarities. Figure 2 shows I-V curve of TSO (1,2) sample with a forward bias, which sample has the lowest Ti content among four samples. The nonlinearity in the I-V curve is clearly shown and varistor voltage is about 7 V. The nonlinear coefficient is 13.6, which is larger than other report’s value of thin film varistor. On the other hand, with a reverse bias, nonlinear coefficient of 4.2 was obtained. The asymmetric behavior indicates that the carrier conduction is dominated by interface of electrode and TSO. When a forward bias is applied, potential barrier is larger than a reverse bias is applied, due to different distribution of space charge with both polarities. Varistor voltages and nonlinear coefficient for four samples are listed in Table 1. As the Ti content decrease, varistor voltage increase and nonlinearity is higher. This result can be inferred from the space charge region is wider due to higher band gap in case of TSO (1,2). In case of TSO (2,1) and (3,1), the varistor characteristics disappear when a reverse bias is applied. When we replace the Mo top electrode with the Al electrode, similar tendency was obtained and it is not shown here, which may be due that work functions of Al and Mo is similar each other. As a result, thin film varistor of TSO using PEALD was successfully grown in our experiments. ITO

Corrosion effects following the etching of Al(Cu 1%) using a SiCl 4 /Cl 2 /He/CHF 3 gas plasma have been evaluated. The phenomenon has been studied using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Auger electron spectroscopy (AES). It was found with SEM that the surface of Al(Cu 1%) was mainly corroded at the grain boundary. Using AES point analysis, the cause of selective corrosion at the grain boundary of Al(Cu 1%) has been investigated. The fluorine (F) and chlorine (Cl) on the etched Al(Cu 1%) have been analyzed with AES. The results showed that the contents of F and Cl on the post-SF 6 treated Al(Cu 1%) were different at each of the analyzed positions such as the grain boundaries and crystalline regions. This seems to result from the imperfect crystalline structure of Al(Cu 1%) grain boundaries. The effects of subsequent in situ SF 6 . plasma treatment on the etched Al(Cu 1%) has been also examined using XPS. It was also confirmed that F has passivated the Cl compounds. The AES and XPS results imply that Cl incorporated at the grain boundaries of the polycrystalline Al(Cu 1%) film accelerated the corrosion and could not be easily removed by subsequent SF 6 plasma treatment.

The microvoids at the interface of direct bonded silicon wafers were studied in view of surface damage, micro particles, and micro gas trap. The microvoids due to surface damages at the edge of wafer and micro particles could be mostly avoided by giving careful handling to wafers and using fresh hydrophillizing solution, respectively. The micro gas trap voids, mostly with diameters in the range of 20-400 ㎛, have been observed at all of Si-Si, Si-SiO₂, and SiO-SiO₂ bonding interfaces. The effects of highly pressurized 50℃ nitrogen flow on wafer surface, ambient gases at mating, and annealing temperature on the generation of micro gas trap voids were studied to clarify the causes of micro gas trap voids. These studies presented that the tendency of the generation of micro gas trap void sensitively depended upon the process conditions related to the surfaces of wafers, especially on the heated high pressure nitrogen showering on the surface before mating.

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The antireflection (AR) properties of Al 2 O 3 and Al x Ti 1―x O y films were investigated for the application of an AR coating of thin-film solar cells. Their optical transmittance was measured to exceed 85% over the entire visible and near-IR spectrum. The AR layers of these films coated on transparent conductive oxide (TCO)/Si exhibited 18% lower reflection than an uncoated TCO/Si at wavelengths from 400 to 900 nm. Furthermore, the thicknesses of the AR layers and TCO were demonstrated to influence the amount and shape of reflectivity in the reflection curves for the AR/TCO/Si structure.

The electrical characteristics of a transistor on a transferred silicon ribbon are demonstrated. The process temperature is limited to 200°C for potential use on plastic sheets. Additional hydrogen annealing reduces the threshold voltage and improves the transistor properties. A high mobility of around 160 cm 2 /V s, with a high on/off ratio and an off current of as low as < 10 11 A, is achieved. The flexibility of the device is evaluated after applying stress in the bended condition. The device shows very little change in properties with a bending radius

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p-Type ZnO thin turns were prepared on phosphorus (P)-doped poly-Si by sputter deposition under various ambient ratios of Ar and O 2 and subsequent annealing process at temperatures ranging from 400 to 600°C. The effects of the ambient sputtering gas and annealing temperature on the electrical and material characteristics of ZnO films were investigated. The formation of p-ZnO film on P-doped poly-Si was confirmed through comparisons involving the conduction type of the ZnO film deposited on insulating SiO 2 . The film deposited in Ar ambient and annealed at 500°C showed a maximum hole concentration of 5.92 X 10 19 cm -3 .

W- and Ti-doped thin films were deposited onto sapphire by the sol-gel method. Both films were grown with (020)-preferred direction. Doping of W had a great effect on the transition behaviors. A 1.2 atom % W-doped film showed a largely reduced resistance in the insulator state and decreased the transition temperature to . However, Ti-doped film had a little change of the transition temperature, and it was , even for the 20 atom % Ti doping. The resistance in the metal state was very large, which means a markedly small change of the resistance at the transition temperature. Further study is required for understanding the effects of doping film with metal ions.

V 2 O 3 films fabricated on (1010) or (1012) Al 2 O 3 substrates in a sol-gel process and subsequent annealing in a very low pressure exhibited an abrupt and large metal-insulator transition (MIT) near -104°C on heating. In this study, VO 2 films initially formed by a sol-gel process were effectively reduced to V 2 O 3 at an annealing temperature of ≥550°C in a vacuum without reducing gases. The V 2 O 3 films exhibited resistance changes as large as 2 X 10 4 -2 X 10 5 due to MIT with annealing temperatures ranging from 550 to 650°C, which are much lower than the process temperature reported in earlier studies.

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The effect of the dielectric constant and surface roughness of gate dielectrics on the electrical performance of pentacene-thin-film transistor (TFT) was investigated using high-K ZrO 2 films deposited by plasma-enhanced atomic layer deposition. The dielectric constant of ZrO 2 (κ ZrO 2 ) was in the range of 15.6-33.0, and the surface roughness was increased with κ ZrO 2 in the presently reported devices. Threshold voltage and subthreshold swing were effectively reduced with increasing κ ZrO 2 and were remarkably low, with values of -0.42 V and 0.15 V/dec, respectively, when κ ZrO 2 = 33.0. To the contrary, the carrier mobility was determined by the surface roughness of ZrO 2 gate dielectrics.

Pentacene organic thin-film transistors (OTFTs) were fabricated on a polyethersulfone (PES) substrate with an Al 2 O 3 gate dielectric grown at 150°C by plasma enhanced atomic layer deposition. Due to the roughness of the Al 2 O 3 surfaces, the OTFTs with Al 2 O 3 of 150 nm showed better performance compared to that with Al 2 O 3 of 120 nm. When OTFTs with a 150 nm thick Al 2 O 3 layer were fabricated on PES substrate, excellent electrical characteristics were obtained, including carrier mobility as large as 0.62 cm 2 /V s, a subthreshold slope as low as 0.4 V/dec, and on-off current ratio as large as 10 7 .

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We report on the fabrication of dual-gate organic thin-film transistors using plasma-enhanced atomic layer deposited 150 nm thick Al 2 O 3 and 300 nm thick parylene as gate dielectrics and pentacene as a semiconductor. The threshold voltage (V th ) is changed from 14.5 to -1.5 V when the voltage bias of the top-gate electrode is changed from -10 to 20 V. The voltage transfer characteristics of an inverter with a dual-gate driver transistor and a single-gate load transistor, specifically, swing range and inversion voltage, have been artificially controlled by changing the voltage bias of the top-gate electrode.

We studied the characteristics of ZnS:Mn thin-film electroluminescence (TFEL) display devices in which the glass substrate had been modified with a two-dimensional (2D) SiO 2 corrugated photonic crystal (PC) pattern. The finite-difference time-domain (FDTD) method was used to predict the behavior of 2D corrugated PC ZnS:Mn TFEL devices with varying PC structural parameters. Based on the optimal parameters derived from the FDTD calculations, a 2D SiO 2 corrugated PC layer was introduced onto the glass substrate of a typical ZnS:Mn TFEL structure by two-step irradiated hologram lithography and reactive ion etching. Experiments conducted under typical operating conditions showed that incorporation of the 2D corrugated structure improved the light extraction luminance at 40 V above the threshold voltage by over 3.1-fold compared to the conventional ZnS:Mn TFEL device, without noticeable degradation of the electrical characteristics. This improvement originates from the liberation of the photons trapped in the high-index guiding layers.

The electrical properties of aluminum silicate (AlSi x O y ) films grown at 120 and 150°C by plasma-enhanced atomic layer deposition were investigated for the application on flexible devices. AlSi x O y films with dielectricconstants of 5.6 and 6.8 exhibited a reduced hysteresis voltage in capacitance-voltage curves compared to Al 2 O 3 films, indicating an improved interfacial quality. The leakage current density for AlSi x O y is comparable to that for Al 2 O 3 . Moreover, the results indicate that the insertion of SiO layers suppresses the film crystallization and the formation of an interfacial layer.

Highly oriented VO 2 thin films were grown on sapphire substrates by a sol-gel method which includes a low-pressure annealing in an oxygen atmosphere. This reduction process effectively promotes the formation of the VO 2 phase over a relatively wide range of pressures below 100 mTorr and temperatures above 400°C. X-ray diffraction analysis showed that as-deposited films crystallize directly to the VO 2 phase without passing through intermediate phases. VO 2 films have been found to be with [100]- and [010]-preferred orientations on Al 2 O 3 (1012) and Al 2 O 3 (1010) substrates, respectively. Both films undergo a metal-insulator transition with an abrupt change in resistance, with different transition behaviors observed for the differently oriented films. For the [010]-oriented VO 2 films a larger change in resistance of 1.2 X 10 4 and a lower transition temperature are found compared to the values obtained for the [100]-oriented films.

The use of TiON films by plasma-enhanced atomic layer deposition as insulators in thin film electroluminescent (TFEL) devices was examined and compared with that of TiO 2 by ALD. A ZnS:Mn TFEL device using AlON-TiON stacked insulator (ATON) exhibited the figure of merit of 12 μC/cm 2 . The luminance of the TFEL device with an ATON insulator was twice as high as that with a conventional Al 2 O 3 insulator. This high performance can be attributed not only to high dielectric constant of the ATON film, but the improved quality of the interface of the phosphor and insulator, as well.

High-quality TiO 2 films were grown at 250°C by plasma-enhanced atomic layer deposition (ALD) with a mixture of O 2 and N 2 plasma for the first time. The films exhibited an improved uniformity of within ′3%, a reliable growth rate of 0.042 nm/cycle, and improved electrical properties, including dielectric constant and leakage current compared to those prepared by conventional ALD. In particular, the plasma process enhanced the rate of adsorption of precursors during the initial growth stage by generating new active functional groups and the surface roughening was suppressed.

Very uniform Al 2 O 3 films could be deposited on polyethersulfone (PES) by plasma-enhanced atomic layer deposition (PEALD) using O 2 as O-precursor at temperatures ranging from 90 to 150°C. Although the use of rf plasma was prone to induce bending of the plastic substrate, lowering rf power and deposition temperature could eliminate the bending of the PES substrate in PEALD of an Al 2 O 3 layer. At 100°C, Al 2 O 3 films were deposited successfully by PEALD with 0.3 s rf pulse width and 300 W, with no measurable bending of substrate and decrease of deposition rate. The etch rate of PEALD Al 2 O 3 films deposited at 100°C, was slow as a factor of 2.6 compared to that of ALD Al 2 O 3 films deposited at 100°C.

Highly uniform ZrO 2 films were deposited by plasma enhanced atomic layer deposition (PEALD) using tetrakis(ethylmethylamino)zirconium (TEMAZ) and O 2 as precursors. The deposition rates were 0.14 and 0.11 nm/cycle at temperatures of 110 and 250°C, respectively. ZrO 2 films deposited at 150°C contained ∼3% nitrogen, incorporated from the Zr-precursor, which contains four amino-groups. In the absence of a plasma, a ZrO 2 film was not deposited with TEMAZ and O 2 at 150°C. The electrical characteristics including breakdown strength and permitivity were also evaluated. The permitivities for 110°C- and 200°C-ZrO 2 films were 16.1 and 26.9, respectively.

A two-layer oxide comprised of SiO 2 and Al 2 O 3 grown at 150°C by atomic layer deposition (ALD) was investigated as the gate insulator for ultralow temperature poly-Si thin-film transistors (ULTPS TFTs). The two-layer gate insulator satisfied good interface quality and low leakage current at the same time. Using this material, n-channel ULTPS TFTs were fabricated on poly-Si with a threshold voltage of 2.3 V and a field-effect mobility of 104 cm 2 /V s without hydrogenation.

The effects of electron (e)-beam irradiation on the luminescent and the materials properties of CaS:Pb films were investigated using structural and compositional analysis techniques. Continuous e-beam irradiation on CaS:Pb thin film for 180 min resulted in an approximately 60% decrease of cathodoluminescence (CL) intensity. Transmission electron microscopic analysis indicated that e-beam irradiation induced the precipitation of Pb. The decrease of CL intensity by e-beam irradiation was mostly caused by the decrease of Pb 2 + luminescent center ion concentration due to the precipitation of Pb. E-beam irradiation also resulted in heavy carbonaceous contamination on the surface. The thickness of the carbonaceous layer was approximately 10 nm.