AVS1996 Session TF-MoP: Thin Film Poster Session I

Monday, October 14, 1996 5:30 PM in Ballroom A

Monday Afternoon

Time Period MoP Sessions | Topic TF Sessions | Time Periods | Topics | AVS1996 Schedule

TF-MoP-1 The Production of Large Area Ultrathin Si Membranes S. Utteridge, Z. Fang, M. Vos (Flinders University of South Australia) The production of free standing Silicon membranes has been achieved by a wide variety of techniques [1]. For our application, the measurement of the electronic structure by transmission (e,2e) experiments, it was necessary to produce extremely thin (10 nm) films over an area of 1 mm! This was accomplished by a combination of wet and dry etching techniques. As a starting point we use a SIMOX crystal with the siliconoxide layer at a depth of 150-200 nm. The oxide layer has the property that it effectively stops certain wet etching processes (e.g. EDP). After the EDP etch the oxide was removed by an HF dip. The sample was transferred to the vacuum and further etched using an RF plasma discharge in a CF4/O2 mixture. The thickness of the film was monitored using interferometry and a HeNe laser. The crystallinity of the layer was checked by transmission electron diffraction. In this way it was possible to obtain the 10 nm thick single crystal membranes in a routine fashion. Besides the stepwise procedure how to obtain these films we present the first results of our (e,2e) experiments. In (e,2e) measurements one obtains the energy-resolved momentum densities [2]. These measurements show the electronic structure of silicon but are also affected by diffraction effects of the incoming electron beam.[1] K.C. Lee J. Electrochem. Soc. 137 (1990) 2556 [2] M. Vos and I. E. McCarthy, Rev. Mod. Phys. 67 (1995) 713
TF-MoP-2 STM/STS Characterization of Diamond Films Prepared by RF Plasma CVD with OH Radical Injection M. Ito, K. Murata, H. Ito, M. Hori, T. Goto (Nagoya University, Japan); M. Hiramatsu (Meijo University, Japan) Recently, diamond thin films have attracted much attention since the invention of the method of its gas phase synthesis because of its applications to electronic devices. We have invented a new method of diamond film synthesis using the RF CH\sub 3\OH plasma CVD with OH radical injection. By using this method, the diamond thin films have been successfully synthesized in capacitively coupled RF (13.56MHz) CH\sub 3\OH plasma reactor. This fact indicates the possibility of depositing uniform diamond thin films in wide area. However, the initial stage of nucleation and the electronic structure at the surface are not well known in the film prepared by RF CH\sub 3\OH plasma CVD with OH radical injection. Therefore, we investigated the nucleation of the diamond film using a scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) in UHV. As a result, we found that the diamond nuclei, and the interface layer between a substrate and a diamond film can be easily distinguished by using STM/STS, and so the interface was identified as an amorphous carbon layer. Moreover, we studied the electronic structure at the surface of the films prepared by RF CH\sub 3\OH plasma CVD with OH radical injection. The electronic structure was very different from that of hydrogen terminated diamond films, which indicate p type electronic structure. The structure was identified as n type electronic structure at the surface by using STS. On the basis of these results, we will discuss the mechanism of the diamond growth in the RF CH\sub 3\OH plasma CVD with OH radical injection.
TF-MoP-3 Microstructure and Surface Morphology of Thin Metal Films Studied by Atomic Force Microscope L. He, J. Siewenie (Northern Illinois University); Z. Shi (Hughes STX Corp.) Atomic force microscope(AFM) was utilized to study the microstructure and surface morphology of metal thin films. The metal films of Au and Al were deposited by thermal evaporation with substrates at low temperature of 77K (LT). For comparison purpose, the same films were also prepared at room temperature of 300K (RT). Our previous study has demonstrated several unique properties of these LT films which could lead to wide device application. When the LT film was used as the Schottky contact metal, it greatly increased the barrier height and enhanced the electrical performance of the device. The other most interesting property of the LT film is its low resistivity at very thin thickness. The films with different thickness were used for this study. At 100\Ao\, the LT Au film was found consisting of smaller-sized grains which, showing smoother surface morphology, while the RT Au film appeared to be rougher on surface. At 200\Ao\, the LT Au film showed much larger-sized grains. However, the 200\Ao\ RT Au film did not show change on its surface morphology. For the Al films, with a thickness of 100\Ao\, it showed smaller-sized grains for both LT and RT samples. With the thickness increasing to 200\Ao\, the LT Al film showed much larger-sized grains similar to that of the 200\Ao\ Au LT film. The 200\Ao\ RT Al showed smaller-sized grains as observed in RT Au films. From AFM study, it is proposed that the LT deposition resulted in a large-sized 2-dimensional particle base, and they extended vertically with the increase of thickness. This is in good agreement with the low resistivity of the LT films since larger grains resulted in less scattering. The potential applications of the LT thin metal films in optoelectronic device will also be discussed in this paper.
TF-MoP-4 Highly Conductive and Transparent Al-doped ZnO Thin Films Prepared by XeCl Excimer Laser Ablation K. Imaeda, M. Hiramatsu, M. Nawata (Meijo University, Japan) Aluminum-doped zinc oxide (AZO) thin films have attracted considerable attention for transparent conducting films in place of indium tin oxide (ITO). For the practical use, it is necessary to lower the process temperature while improving the quality and growth rate of the AZO thin films. In this work, transparent conducting AZO thin films have been prepared using pulsed laser ablation method. A XeCl excimer laser (308 nm) was used for ablation of AZO bulk target. The excimer laser beam was focused onto the target in the deposition chamber through a quartz lens and a quartz window. The energy density of excimer laser beam at the target surface was maintained at 1.5 J/cm\super 2\ and the repetition rate was 5 Hz. The laser pulse duration was 20 ns. The target was a sintered ZnO disc containing excess Al\sub 2\O\sub 3\ of 0-5 wt%. Typical deposition rate of AZO films was 10 nm/min. The substrate heating was carried out using a continuous wave CO\sub 2\ laser. The effects of substrate temperature and oxygen gas pressure on the electrical and optical properties of the films deposited in an oxygen atmosphere were investigated. The c-axis oriented AZO films were successfully grown at substrate temperatures ranging from room temperature to 300 C in an oxygen atmosphere. Optical transmittance above 85% was observed in the visible region of the spectrum for the 450 nm-thick film deposited from the ZnO target doped with 1 wt% Al\sub 2\O\sub 3\. Resistivity of 1.34 x 10\super -4\ Ohm-cm was obtained at a low substrate temperature of 200 C.
TF-MoP-5 A Technique for Coating Inner Walls of Long Glass Tubes with Tin Oxide Thin Films. M. Ding (Beijing Vacuum Electronics Research Institute, P.R. China) To obtain a uniform coating on inner walls of a long glass tube has been a difficult task. With the request of a plasma research lab at Maryland, we have developed a technique for coating the inner walls of a one-meter-long glass tube (3.8 cm in diameter) with Tin Oxide (TO) or Indium Tin Oxide (ITO), using a low temperature CVD process. In doing so, we have designed a fogging spraying apparatus, which had a two-meter-long quartz tube of 6 cm in diameter for supporting the glass tube to be coated. The glass tube was heated by a 1.5-meter-long cylindrical furance. The chemical mist from a fogging system was transported via the glass tube from one end of the tube. By properly designing a temperature profile of the furance and choosing specific deposition parameters, we have successfully fabricated resistive wall tubes for plasma research. The total resistance of the tubes was around 4 kohms, with a sheet resistance deviation of less than 10% and transmission of light better than 85%. The three most important factors for attaining a uniform coating without moving the spraying nozzle were: the temperature of the glass tube, the flow rates of carrier gas and solution.
TF-MoP-6 In Situ Characterization of Whiskers on Al Films for Thin-film Transistor-liquid Crystal Displays by High Voltage Electron Microscopy K. Tsujimoto, N. Miura (ITES Co. Ltd., Japan); K. Kuroda, H. Saka (Nagoya University, Japan); H. Takatsuji, S. Tsuji (IBM Japan, Ltd.) Thin-film transistor-liquis crystal displays (TFT-LCDs) are now wisely used for personal computer displays. In accordance with the larger-sized and higher resolution, thin-film Al materials are of great technological interest due to their low resistivity. The whisker formation of thin Al films is one of the major concern affecting the yield loss in TFT fabrication. To suppress whisker growth, it is necessary to investigate the mechanism of whisker formation. Several studies concerned with hillock formation of Al film on silicon substrates have been reported. Comparatively, however, little is known about whisker growth behavior of Al films on glass substrates using transmissi onelectron microscope (TEM), because it is difficult to use with the very thin glass specimens that are needed. This paper presents in situ fabrication and observation of Al whiskers. We developed the technique to fabricate Al whiskers using nanoindentation techniques with heating in TEM. This technique allows to study whisker morphology. Because Al whiskers ranged from 300 to 400 nm in diameter and the longest whisker attained a length of 10 \mu\m, it is thin enough to high voltage (1 MV) electron transparancy to observe whiskers in detail. We found that whisker formation was completed within several second s.The TEM results revealed the nanostructure of as-grown whiskers as the singl e crystal. We also demonstrated the sample preparation method for cross-section of indivisual whiskers, using focused ion beam etching. Both bright and dark field TEM images provised the morphological and crystallographical information of the whisker/Al film interface. The prior orientation of whisker growth will be discussed.
TF-MoP-7 The Effect of Grain Nanostructure and Orientation on the Whisker Growth in Al Conductor Layers of Thin-film Transistor-liquid Crystal Displays H. Takatsuji, S. Tsuji (IBM Japan, Ltd., Japan); K. Tsujimoto, N. Miura (ITES Co. Ltd., Japan); K. Kuroda, H. Saka (Nagoya University, Japan) Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are now widely used as elements in active-matrix liquid crystal displays (AM-LCDs) . Decreasing the resistivity of a gate metal is of great practical importance in TFT-LCD technology. High-pixel-density TFT-LCDs require a high-current-driving capability for TFTs. Thin-film Al materials are of great technological interes t due to their low resistivity. The hillock and whisker formation of thin Al fil msare one of the major concern affecting the yield loss in TFT fabrication. Several studies concerned with electromigration of Al films on silicon substra tehave been reported. However, little is known about thermomechanical behavior of Al films on glass substrates. The motivation for this work was to characterize the nanostructure of various sputtered Al films, and to assess the role of grain size and crystallographic texture on the whisker formation. Thin Al film s were deposited on LCD-grade large glass substrates in single-substrate type an d in-line type chamber. The morphology of as-deposited Al films (350-nm-thick) was characterized in detail by atomic force microscopy (AFM). All metallizatio nsexhibited a near-(111) fiber texture, as determined by x-ray diffraction (XR D) analysis and transmission electron microscopy (TEM) observation. A degree of (111) preferred orientation of Al films deposited in the in-line type chamber was three times as much as those of single-substrate type chamber. This low degree in this chamber was related to the mismatch of magnet pass number durin g sputtering. The relationship between whisker formation and the degree of (111) preferred orientation was obtained from the patterned films. A high degree of (111) preferred orientation was found to be more dependent on the magnet pass number, substrate temperature, and sputtering pressure than on the power of sputtering. Moreover, the improvement of sputtering conditions for single- substrate type chamber correlated to the whisker formation resistance.
TF-MoP-8 Relationship between Texture and Hillock Formation in Sputtered Al-0.2%Cu Thin Films S. Tsuji, H. Takatsuji (IBM Japan, Ltd.); K. Tsujimoto, N. Miura (ITES Co. Ltd., Japan); K. Kuroda, H. Saka (Nagoya University, Japan) The hillock formation of thin Al and Al-based alloy films is one of the major concern affecting the yield loss in high-resolution thin-film transistor - liquid crystal displays (TFT-LCDs) manufacturing. The degree of hillock formation depends on their nanostructure. The relationship among the grain structure, texture, and hillock formation of Al-0.2%Cu metallizations produced under similar sputtering conditions was explored. Thin Al-0.2%Cu films were sited on LCD-grade large glass substrate in single-substrate type chamber (100, 175, and 350-nm-thick). To investigate the influence of underlying layer , thin Mo films (50 and 100-nm-thick) were sited in some conditions. The morphology of as-sited films cut from the center and edge region of large glass substrate have been investigated in detail by atomic force microscopy (AFM), to evaluate the film uniformity. Grain size of the center was larger than that of the edge in all metallizations. Cross-sectional transmission electron microscopy (TEM) was also used to investigate the nanostructure.The degree of (111) preferred orientation was measured by x-ray diffraction (XRD) method. The film sited on Mo underlying layer (100-nm-thick) exhibited a good texture, as determined by XRD analysis. To improve the characterization method for hillock formation, we developed the nanoindentation techniques to the films on glass substrates with heating in a vacuum furnace. We demonstrate d that our technique was capable of high hillock formation rates, which allowed rapid investigation. By this technique, the high degree of hillock formation correlated to the weak hillock formation resistance.
TF-MoP-9 Effects of Rapid Thermal Annealing and CdS Substrate Preparation on CdTe Thin Film Solar Cell Properties Y. Cho, G. Yeom (Sung Kyun Kwan University, Korea); K. Oho, J. Yoon, S. Shin, K. Park (National Institute of Technology and Quality, Korea) Rapid thermal annealing(RTA) is widely used for semiconductor integrated circuit fabrication to anneal the process-induced defects without enhancing the inter-diffusion of materials. Currently, furnace annealing is generally used after the deposition of polycrystalline p-CdTe thin films on polycrystalline n-CdS/ITO glass substrate to remove defects formed on CdTe during the evaporation. However, furnace annealing can degrade CdTe/CdS junction properties through the inter-diffusion. In this study, to anneal the evaporated CdTe on CdS/ITO glass substrate, RTA is applied and its effects on microsrtucture, diffusion properties, and solar cell efficiencies are investigated. Cross-sectional transmission microscopy(XTEM) shows that the evaporated CdTe contains microtwins and dislocations, and the grain orientation of CdTe is epitaxially related to CdS grain orientation, and the grain size of CdTe is comparable to that of CdS. RTA of the evaporated CdTe reduces dislocations in the grains and the inter-diffusion between CdTe and CdS. After the RTA, the composition of CdTe changes to Cd\sub 44\Te\sub 44\S\sub 2\, whereas, after furnace annealing, it changes to Cd\sub 40\Te\sub 40\S\sub 20\. Therefore, the reduction of inter-diffusion by RTA is obtained as expected, however, the grain size remains small as deposited. Larger CdTe grains are obtained by using larger CdS grains deposited on ITO by close spaced sublimation technique. The combination of large CdS grained substrate and RTA of CdTe after the deposition shows the best overall CdTe properties.
TF-MoP-10 A Morphological Study of GaAs Grown by Periodic Supply Epitaxy on (111)B Substrates F. Allegretti (Imperial College, United Kingdom); G. Bacchin, K. Tsunoda, T. Nishinaga (University of Tokyo, Japan) True selectivity was obtained on (111)B GaAs substrates masked by SiO\sub 2\ and patterned, by employing the Periodic Supply Epitaxy technique [1] at temperatures between 580 and 630 C. Selective growth of GaAs was carried out by Molecular Beam Epitaxy (MBE) using solid sources of Ga and As \sub 4\. Lateral migration of atoms across the SiO\sub 2\ mask surface was shown to give an important contribution to the growth. A wide zone clear of polycrystalline deposits was obtained around each window, whose length was dependent on both the window orientation and the density of nucleation sites on the mask surface. Its maximum length was 78 \mu\ m. An increase in defect density on the mask, experimentally induced by electron bombardment, caused a drastic reduction of the length of the clear zone. GaAs was deposited on (111)B substrates in holes of different diameters and the morphology of the grown layers was investigated by atomic force microscopy, Nomarski optical microscopy and scanning electron microscopy. The grown layers were not planar but developed sidewalls. Holes bigger than 1.5 \mu\m in diameter were not totally filled during growth, a wide range of facets was developed and the top surface of the structures was a flat (111)B plane. Sharp pyramidal structures bounded by neat and flat [110] facets were obtained in holes smaller than 1.5 \mu\m. The PSE technique appears therefore to be very promising for the formation of quantum dots directly in situ during the MBE growth process. [1] F. E. Allegretti and T. Nishinaga, J. of Crystal Growth 156 (1995)
TF-MoP-11 Preparation of Highly Transparent and Conductive Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ Films by DC Magnetron Sputtering T. Minami, Y. Takeda, T. Kakumu, S. Takata, I. Fukuda (Kanazawa Institute of Technology, Japan) Recently, the preparation of a transparent conducting thin film using a ternary compound composed of Ga\sub 2\O\sub 3\ and In\sub 2\O\sub 3\, GaInO\sub 3\, has been reported. In this paper, highly transparent and conductive Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ films prepared by dc magnetron sputtering are described. The sputter depositions were carried out at pressures of 0.1 to 1.0 Pa in an Ar atmosphere with a power of 50 W using In\sub 2\O\sub 3\-Ga\sub 2\O\sub 3\ targets with a Ga content (Ga/(Ga+In) atomic ratio) of 0 to 0.6. The electrical, optical and chemical properties of the deposited In\sub 2\O\sub 3\-Ga\sub 2\O\sub 3\ films were strongly dependent on the target composition. The minimum resistivity of films prepared on substrates at room temperature was obtained using a target with a Ga content of about 0.3, and that of films prepared at 350\super o\C was obtained with a Ga content of about 0.4. A resistivity as low as 5x10\super -4\ \Omega\ cm was obtained in Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ films prepared on substrates at room temperature. A sheet resistance of 1 k \Omega\/sq and a transmittance above 95% in the visible range were obtained in a 20 nm thick film. The refractive index of deposited Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ films was about 2, and the band-gap energy was about 3.4 eV. The etching rate in HCl solution increased as the Ga content was increased. The Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ films having the minimum resistivity were easily etched in 0.2M HCl at room temperature. Thus we can conclude that Ga\sub 2\O\sub 3\-In\sub 2\O\sub 3\ films are promising materials, especially as transparent electrodes for flat panel displays.
TF-MoP-12 New Multicomponent Oxide Thin Film Gas Sensors with High Sensitivity for Chlorine Gas T. Miyata, T. Minami, M. Ishii, K. Shimokawa, T. Kakumu (Kanazawa Institute of Technology, Japan) In many industrial processes, the detection of chlorine gas is very important. In this paper, we demonstrate new chlorine gas sensors using multicomponent oxide thin films consisting of Zn\sub 2\In\sub 2\O\sub 5\ and MgIn\sub 2\O\sub 4\ system. Films were prepared by conventional rf magnetron sputtering on substrates using powder targets composed of ZnO, MgO and In\sub 2\O\sub 3\. The sensitivity of sensor is defined as ((R0-R)/R0)X100%; R0 and R are resistance of sensor before and after testing gas introduction, respectively. The value of sensitivity becomes negative when the resistance of sensor is increased by the exposure. Sensors using Zn\sub 2\In\sub 2\O\sub 5\-MgIn\sub 2\O\sub 4\ films exhibited a high sensitivity and an excellent selectivity for chlorine gas in air: the sensors exhibited an increase of resistance with exposure to chlorine gas, whereas they exhibited a decrease of resistance for various inflammable gases. The sensing properties of Zn\sub 2\In\sub 2\O\sub 5\-MgIn\sub 2\O\sub 4\ film sensors were strongly dependent on the composition in their films. The sensitivity of a Zn\sub 2\In\sub 2\O\sub 5\-MgIn\sub 2\O\sub 4\ film sensor prepared with a Zn\sub 2\In\sub 2\O\sub 5\ content of about 60 mol% was about -300% when the sensor was exposed to chlorine gas with a concentration of about 1 ppm. The increase of resistance is attributed to the trapping of free electrons by chlorine being adsorbed on grain boundaries and/or the film surface.
TF-MoP-13 Growth and Characterization of Lennard-Jones Thin Films J. Beasock, H. Helbig, G. Ramseyer, L. Walsh (Rome Laboratory) One of the major hurdles to overcome in molecular dynamics simulations of diffusion-determined phenomena such as electromigration is the preparation of a representative sample having "realistic" grain orientations and grain boundaries. Natural samples have grain structures that are dependent on the crystal habit of the deposited material, the substrate surface morphology and the thermal history. We simulated the deposition of a Lennard-Jones thin film containing about 10,000 atoms on an idealized (featureless) substrate with dimensions 120 by 50 angstroms\\super 2\|. The growth conditions and characteristics of the film as deposited and after annealing are presented.
TF-MoP-14 Dose and Ion Current Dependence of the Topography formed on the Surface of Ag/Cu Two-Phase Alloys Sputtered by 600 eV Ar\super +\ K. Pierson, C. Hawes, T. Krueger, J. Stupak (University of Wisconsin, Eau Claire) The polished surface of a Ag/Cu (60/40 % atomic) alloy sample held at room temperature was bombarded with varying fluences (7x10\super 16\ to 7x10\super 19\ ions/cm\super 2\) of normally incident 600 eV argon ions at 1.0 mA/cm\super 2\.The changes in surface topography progressed through various stages. For fluences less than 10\super 18\ ions/cm\super 2\, selective sputtering of the higher yield Ag grains caused them to become recessed. Between 10\super 18\ ions/cm\super 2\ and 10\super 19\ ions/cm\super 2\ an abrupt transistion to seed cone development occurs only on the surface of the Ag grains. The dense large aspect ratio cones decrease the sputtering yield of the Ag grains with the result that they now become raised above the Cu grains. At fluences greater than 10\super 19\ ions/cm\super 2\ the entire surface of the sample becomes densely covered with large aspect ratio cones.
TF-MoP-15 Thin Film Epitaxy of Layered GaSe on Sapphire by Molecular Beam Epitaxy S. Chegwidden, F. Ohuchi (University of Washington) Despite lattice and thermal mismatch, epitaxial films of GaSe have been grown on GaAs and single crystal alumina substrates. Prior studies, using a single GaSe knudsen cell, have shown that growth of GaSe on GaAs 111 A and B substrates leads to island growth morphologies. These films grow with the c-axis perpendicular to the substrate. Both film and substrate have hexagonal symmetry and films assume a preferred alignment on the substrate. Recent studies have investigated the growth of GaSe on c-axis alumina, single crystal GaSe, and arsenic terminated silicon (111) substrates. Deposition takes place at growth temperatures near 540 degrees C using a single GaSe knudsen cell in the presence of a selenium over pressure which is controlled by a selenium knudsen cell. Various Se to GaSe flux ratios have been studied in an effort to control growth modes and ultimate morphology. Growth of GaSe on any substrate becomes homoepitaxy after the first monolayer of coverage; so growth on the basal plane of single crystal GaSe is a unique system to study the growth morphology and optimize growth parameters of GaSe on other substrates. In-situ characterization of growth is performed with RHEED to monitor the quality of the growth, and XPS is used to verify the chemical purity and stoichiometry of the films. Further ex-situ analysis is carried out with XRD to verify that the films are growing along the c-axis of GaSe, and AFM to measure roughness, orientation, and grain sizes to study nucleation and growth modes for these films. Ellipsometry is used to measure film thickness and calibrate growth rate measurements. The goal of the work is to determine optimal growth conditions to produce GaSe thin films of optical purity, in order to investigate device applications which exploit the optical properties of GaSe.
TF-MoP-16 Growth of High Quality AlAs/AlGaAs Layers by Molecular Beam Epitaxy for Quarter-wave Mirror Stacks for Verticle Cavity Devices and Wavelength Selective Waveguides N. Bojarczuk, S. Guha (IBM T.J. Watson Research Center); B. Pezeshki (Spectra Diode Labs); F. Agahi (IBM Microelectronics Division) High quality smooth AlAs/AlGaAs layers for quarter-wave mirror stacks for verticle cavity devices have been fabricated by molecular beam epitaxy on (100) GaAs. Monitoring the (3x2) reconstruction surfaces of AlAs and Al\sub x\Ga\sub x-1\As for x = 0.3 has repeatably produced excellent mirror stacks with up to 22 periods of AlAs/AlGaAs couples. Reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM) of the mirror stack interfaces have shown great improvement when this technique has been used to grow the layers
TF-MoP-18 Nano-mechanical, Nano-wear, and Fracture Toughness Tests on Amorphous SiC-N Coatings T. Scharf, J. Barnard (University of Alabama) a:SiC-N films 500nm thick were deposited on oxidized Si(111) wafers at ambient temperatures by reactive magnetron sputtering of SiC in N\sub 2\ discharges. By adjusting the gate valve angle, the respective argon and nitrogen gas flow rates were varied to obtain a given composition. In addition, the total pressures (2.1, 3.1, and 4.1m Torr) were kept constant under these variations in flow rates. The hardness (H) and elastic modulus (E) were assessed via nanoindentation using a sharp Berkovich diamond indenter. The fracture toughness (K\sub IC\) was characterized by modifying the previous nanoindentation technique to a cube corner indenter which under low loads displaced more volume than the Berkovich. This in turn generated increased amounts of stress and strain in the surrounding film, promoting nucleation and propagation of radial indentation cracks. A sphere on flat (magnetic tape) wear tester established the wear scar volume losses as a function of wear time. The arithmetic (R\sub a\) and root mean square (RMS) surface roughness along with bearing ratio (t\sub b\) plots, a statistical measure of the vertical roughness, were quantified by atomic force microscopy (AFM). The composition and structure of the films for all the deposition conditions were qualitatively and quantitatively assessed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDXS) and were subsequently correlated to the overall film properties.
TF-MoP-19 GeSi/Ge Heterojunction Infrared Detectors R. Jiang, S. Gu, N. Jiang, Z. Li, S. Zhu, Y. Zheng (Nanjing University, P.R. China) In 1.3-1.55 \micrometer\ infrared photodetectors, the most commonly used materials are Si, Ge, InGaAsP, etc. Each of them has its own advantages and shortcomings. In order to obtain infrared detectors with simple technology, higher sensitivity and lower dark current than Ge detectors, we have fabricated, for the first time, novel 1.3-1.55 \micrometer\ Ge based GeSi heterostructure infrared detectors. P-type GeSi layer was first epitaxially grown on n-type (100) Ge substrates by Rapid Thermal Process/Very Low Pressure-Chemical Vapor Deposition (RTP/VLP-CVD). Then P-type Si caplayer was deposited. The operating pressure was of the order of 10 mTorr, and the growth temperature was 873K. The growth rate was as low as 0.1nm/sec. These detectors are mesa pn heterostructures. The areas of their photosensitive surfaces ranges from 0.1 to 2.0 mm\super 2\. SiO\sub 2\ films grown at low temperature (573K) are used as the reflection reducing coating. Spectrum response, voltage-current characteristics and detect ing sensitivities of these detectors were measured. The response ranges from 0.9 to 1.8 \micrometer\, with a peak at 1.3-1.55 \micrometer\. The sensitivities R \>=\0.7A/W. At -5V bias, the dark currents were less than that of Ge pn junction detectors. The characteristics of these detectors are much better than Ge pn junction detectors.
TF-MoP-20 Growth and Characterization of Hafnium Nitride Films S. Shah, P. Carcia, M. Reilly (E.I. du Pont de Nemours and Company) Thin films of HfN/sub x/ were prepared by reactive dc magnetron sputtering over a wide range of composition, from pure Hf to HfN to higher nitrides. Film properties and composition were found to vary widely, depending on the process variables. We will discuss the process-composition-property relationship with emphasis on the effect of N content of the sputtering gas and the applied substrate bias on the physical and chemical properties of films. Mononitride of Hf were metallic but higher nitrides show dielectric behavior. As the nitrogen content increased above x=1, films changed from non transparent to transparent in the visible. A multiphase film with tailorable optical and electrical properties can therefore be fabricated and used for specific optical or electrical application. X-ray photoelectron spectroscopy results on the formation of mixed phases with higher nitrides will be discussed.
TF-MoP-21 Photoluminescence and Photoreflectance Studies of Defects in GaAs Epitaxial Layers Grown by LPE under Different Supercooling Temperatures G. Torres-Delgado, J. Mendoza-Alvarez, C. Vazquez-Lopez (CINVESTAV, Mexico); C. Alejo-Armenta (Universidad Autonoma de Sinaloa, Mexico) Using the Liquid Phase Epitaxy (LPE) growth technique, we have grown intrinsic GaAs epitaxial layers. Several layers were grown changing the supercooling parameter, \delta T\, that is the temperature gradient below the equilibrium (Teq) at which the layer growth takes place. Photoluminescence (PL) and photoreflectance (PR) spectroscopic techniques were used in order to study the influence of the supercooling on the defect formation in the GaAs layers. For growth temperatures (Tg) around the equilibrium, the PL spectra show a strong exciton peak and emission bands related to the presence of C and Si impurities, but any low-energy emission bands due to defects are detected. As soon as Tg falls a few degrees below Teq, an emission band centered around 855 nm appears in the PL spectrum, whose intensity increases as Tg decreases. The corresponding PR spectra show well defined Franz-Keldysh (F-K) oscillations. By analyzing these F-K oscillations under the intermediate-electric field regime we show that as \delta T\ increases in the range of 0-15\super o\C, there is a monotonic increase in the density of ionized impurities, in agreement with the results from the PL spectra. We discuss the nature of this type of growth defects, as well as a mechanism of competition between antisites and structural defects which produces a compensation effect that is also observed in the PL and PR spectra.

Time Period MoP Sessions | Topic TF Sessions | Time Periods | Topics | AVS1996 Schedule