AVS2001 Session SS+SC-TuP: Semiconductor Deposition Poster Session

Tuesday, October 30, 2001 5:30 PM in Room 134/135

Tuesday Afternoon

Time Period TuP Sessions | Topic SS Sessions | Time Periods | Topics | AVS2001 Schedule

SS+SC-TuP-1 Fabrication of a-Si:H Films by Plasma CVD
T. Nishimiya (Mitsubishi Heavy Industries Ltd., Japan)
We have succeeded in getting high-deposition rate and high quality for preparing hydrogenated amorphous silicon (a-Si:H) films, as well as micro-crystalline silicon（mc-Si）films, by Very-high-frequency (VHF) plasma CVD using a ladder-shaped electrode. Recently, VHF plasma CVD technique has become one of the topics in the field of the fabrication of solar cell and thin film transistors, because its high plasma density enables high-speed deposition. However, in the large area deposition, which is needed in the application of commercial production, the effective gas flow rate fed into the plasma region limits the deposition rate and the film qualities because the gas depletion condition leads to the degradation of the film quality. We developed the ladder shaped electrode, which has an advantage over a conventional parallel-plate electrode in the controllability of the gas flow. The experiments are performed using a ladder-shaped electrode consisted of 9 stainless-steel rods 160 mmÃ-160 mm in external dimension. The material gases are introduced into the plasma region between each rod of the electrode. Using the VHF-SiH4 plasma at the frequency of 60MHz, we got a-Si:H film at the deposition rate of 1.2 nm/s with the ratio of photo conductivity/dark conductivity of 106. We also applied this electrode to fabricate the mc-Si film and succeed very high-speed of 3.4 nm/s using the plasma of SiH4 diluted with H2 at the frequency of 100 MHz. These were demonstrated that this electrode is highly suitable for the production technique.
SS+SC-TuP-2 Growth Characteristics of Si1-x-yGexCy on Si(100) and SiO2 in Ultraclean Low-Temperature LPCVD
Y. Hashiba, M. Sakuraba, T. Matsuura, J. Murota (Tohoku University, Japan)
The growth characteristics of Si1-x-yGexCy films on Si(100) and SiO2 were investigated. The films were deposited at 550°C in a SiH4-GeH4-CH3SiH3-H2 gas mixture using ultraclean hot-wall low pressure chemical vapor deposition (LPCVD) system. The total deposition pressure was 30Pa, and the partial pressures of SiH4, GeH4 and CH3SiH3 were in the range of 6.0Pa, 0-2.0Pa (Ge fraction x=0-0.57) and 0-0.2Pa (C fraction y=0-0.05), respectively. Si films are epitaxial on Si(100) and amorphous on SiO2. The deposition rate of Si on SiO2 (1.2-1.4nm/min) is 10-20% larger than that on Si(100), however, with the addition of CH3SiH3, the deposition rate on SiO2 decreases to that on Si(100). It is considered that CH3SiH3 molecules are scarcely adsorbed at Si-Si pair site on Si(100) but not at the other sites on amorphous Si surface. With the addition of GeH4, the deposition rate increases and that on Si(100) becomes larger than that on SiO2. Si1-xGex films are epitaxial on Si(100) and <110> or random oriented polycrystalline on SiO2. This is explained by the modified Langmuir-type adsorption and reaction with the assumption that SiH4 and GeH4 are adsorbed more preferentially on the Si-Ge pair site than Si-Si, Ge-Ge pair site, single Si and Ge bond sites. With the addition of CH3SiH3, the deposition rates decreases and that on Si(100) tends to become the same as that on SiO2. It is suggested that the adsorption and reaction of SiH4 and GeH4 are suppressed by the adsorption of CH3SiH3 molecule at the Si-Ge pair site. From XPS measurement, Ge fraction on Si(100) is almost equal to that on SiO2 within 10% error. The relationship among lattice constant, Ge and C fraction is under investigation.
SS+SC-TuP-4 Mechanisms of Vapor Phase Growth of Chalcopyrite Semiconductors
D.-X. Liao, A. Rockett (University of Illinois)
Epitaxial growth of the chalcopyrite-structure semiconductor Cu(In,Ga)Se2 alloys on (111)A and B, (110), and (100) GaAs was studied and a growth model is proposed. These semiconductors are prime candidates for high-efficiency thin film solar cells and have potential in thin film transistor applications. Surface morphologies result from a mixture of surface-energy and nucleation and growth dominated phenomena. Surface energy considerations drive all observed surface planes to decompose into close packed facets, some including large numbers of surface steps. Comparison of the bulk structure and morphologies of the different surfaces indicate that nucleation of surface terraces on close-packed Se-terminated planes and their growth dominates the evolution of surface morphologies. Relatively slow nucleation of terraces on metal terminated close packed planes leaves these very smooth relative to the Se-terminated faces. Structural and electronic properties measurements show that point-defect clusters occur in large numbers in this material and can spontaneously organize on specific planes. The creation of these clusters during facet growth is proposed to be responsible for the observed step motion and consequently for the surface morphologies. Results show that epitaxial temperatures vary significantly from ~700 C on the (111)B surface to ~540 C on (110). The epitaxial temperature is proposed to be related to the availability of Se- and metal-terminated surface step edges. The organization of the point defects during growth appears to lead to a physical separation between the defects responsible for p-type doping and the conduction path for holes, permitting a nearly constant 300K hole mobility of 300 cm2/V-sec over a wide range of hole concentrations.
SS+SC-TuP-5 Studies on Spray Deposited Lanthanum Selenide Thin Films from Non-aqueous Medium
G.D. Bagde, C.D. Lokhande (Shivaji University, India)
Since the discovery of high temperature semiconductor, great efforts have been made to produce high quality thin films of the materials. The rare earth chalcogenides are of interest for applications such as thermoelectric cooler, photoelectric cells, solar cells, cold cathode emitting devices, far infrared window materials etc. The rare earth selenide have shown semiconducting properties used for high temperature device formation. Spray pyrolysis is simple and inexpensive technique for large area deposition of thin films. Spray pyrolysis technique is employed to prepare La2Se3 thin films from non-aquous (methanol) medium. The preparative parameters are optimized to get good quality films. The optimized pyrolysis temperature is 200°C. The La2Se3 film show polycrystalline cubic structure with dominant plane (310). The calculated average grain size is about 40 nm. Scanning Electron Microscopic studies revels that La2Se3 films have porous fibrous network structure and presence of irregular shaped particles. From the analysis of the optical absorption data a direct allowed transition at 2.45 eV has been observed. The room temperature electrical resistivity is of the order of 104-105 Ω-cm. The films are found to be p-type semiconductor by themoemf measurement study.
SS+SC-TuP-6 Studies on Deposition of Indium Sulphide Thin Films by Silar Method
H.M. Pathan, S.D. Sartale, G.D. Bagde, C.D. Lokhande (Shivaji University, India)
Indium Sulphide is a promising material used as a buffer layer in Cu(InGa)Se2 based solar cells and mini models. Successive ionic layer adsorption and reaction (SILAR) is a modified version of chemical bath deposition (CBD) method for thin film deposition. In CBD, when solutions are mixed together, the precipitation on the substrate and in the solution takes place. This results into wasteful and unavoidable formation of bulk precipitation in the solution since the reaction is not controllable. To overcome this difficulty, CBD is modified as SILAR in which substrate is immersed into separately placed cationic and anionic precursors and rinsing before every immersion with ion exchanged water to avoid homogeneous precipitation in the solution. In the present investigation, nanocrystalline semiconducting indium sulphide thin films were deposited onto glass substrates using SILAR method. For the deposition of indium sulphide thin films, preparative conditions such as concentration and pH of precursor solution and adsorption, reaction and rinsing time duration were optimized at room temperature (27 °C). These deposited films were characterized for their structural, optical and electrical properties. The films are found to be nanocrystalline. The films have 2.7 eV direct optical band gap with n-type electrical conductivity.
SS+SC-TuP-7 The Effects of the Microstructure Factor in Chemical Texturization of Crystalline Si Solar Cells
F. Krok (Jagiellonian University, Poland); Z. Swiatek, E. Beltowska-Lehman (Polish Academy of Science); M. Szymonski (Jagiellonian University, Poland)
The texturization of the silicon solar cell front surface improves the cell efficiency due to its antireflection properties and light trapping effect. The chemical texturization of single grains in well-defined multi-crystalline Si wafers was performed in a standard alkaline (anisotropic etching) as well as in acid (isotropic etching) solutions. The microstructure of textured wafers was investigated using SEM, TEM, and NC-AFM methods. The crystallographic orientation of each grain was determined by means of electron back scattered diffraction (EBSD) technique. It comprises the analysis of detected Kikuchi patterns, observed in the SEM. The texturization in alkaline etching solutions causes development of steps between particular grains because of different etching rate in different crystal plane orientation in the wafers. In these cases, although the grains were textured, the grain boundaries became developed and steps were observed. Depending on the grain initial crystallographic orientation (hkl) and the individual disorientation, different final morphologies have been observed. Based on the NC-AFM measurements, the nanostructural nature of the texturized surface was evident for some grain orientations. Moreover, these nanocrystals (ca. 20 nm) have a well-defined preferred crystallographic orientation. The texturized surface with good homogeneity of particular grain orientations of m-c Si has been achieved. The final morphology of the texturized m-cSi surface strongly depends on the process parameters as well as on the polar and azimuthal disorientation of the grain.
SS+SC-TuP-8 Polycrystalline Si Thin Film Growth on Glass using Magnetron Sputtering
M.J. Jung, Y.M. Jung, J.U. Kim, J.G. Han (Sungkyunkwan University, Korea)
Polycrystalline Si thin film is widely applied materials for thin film transistor of Flat Panel Display (FPD), and photovoltaic applications because of its high mobility, electrical conductivity, and high-energy conversion efficiency compared to a-Si.1 Over the past few years, there have been a variety of techniques on thin film growth of poly-Si. Among theses techniques, Solid Phase Crystallization (SPC) and Excimer Laser Annealing (ELA) have been the most frequently used methods. The SPC method has too high crystallization temperature (650°C) for glass substrate. On the other hand, ELA method is suitable for low temperature on the glass substrate, however, there are still problems such as non-uniformity of grain growth on the large area glass substrate as well as expensive processing cost.2 Recently, Metal-Induced Crystallization (MIC) of amorphous silicon has been studied for poly-Si thin films on low temperature glass3. We have deposited crystalline poly-Si thin films on soda-lime glass and SiO2 glass substrate as deposited by PVD at low substrate temperature using high power magnetron sputtering method. The electron mobility of the poly-Si grown on soda-lime glass and SiO2 glass at substrate temperature of 115° show 138 cm square per Volt dot second and 191cm square per Volt dot second. Therefore, to investigate the relationships between surface and film microstructure as well as the nucleation, growth mechanism and its electrical properties of poly-Si thin film, we have studied the variation of plasma state for nucleation and growth mechanism by Langmuir probe and Optical Emission Spectroscopy (OES). The epitaxial orientation, microstructual characteristics and surface properties of the films were analyzed by TEM, XRD, and AFM. For the electrical characterization of these films, its properties were obtained from the Hall effect measurement by the Van der Pauw measurement.
SS+SC-TuP-9 Arsenic Incorporation into Indium Phosphide (001) Surfaces during Metalorganic Vapor-Phase Epitaxy
R.F. Hicks, D.C. Law, C.H. Li, S.B. Visbeck, Y. Sun (University of California, Los Angeles)
The quality of heterointerfaces is of great importance for high performance optoelectronic devices. In this work, we report on a detailed study of the effect of arsenic exposure to indium phosphide (001) during metalorganic vapor-phase epitaxy (MOVPE). Indium phosphide surfaces were exposed to several Torr of tertiarybutylarsine (TBAs) at temperatures ranging from 200 to 600°C. Scanning tunneling micrographs reveal that arsenic exposure below 400°C yields atomically smooth surfaces with ordered reconstructions. These surfaces consist of either a single monolayer of As and P with a (2x1) structure, or half a monolayer of As incorporated into a (2x4) structure. Conversely, at temperatures above 450°C, three-dimensional islands are formed during TBAs exposure. The arsenic coverage in these structures exceeds several monolayers, indicating diffusion into the bulk. The implications of these results for the fabrication of III- V heterojunction devices will be discussed at the meeting.
SS+SC-TuP-10 Synthesis of Sb2Se3 Nanorods under Mild Hydrothermal Conditions
J. Wang, Z. Deng, Y. Li (Tsinghua University, P.R. China)
A hydrothermal reduction route was employed for the synthesis of Sb2Se3 semiconductor nanorods. The reaction temperature for the formation of Sb2Se3 nanorods was found to be above 130°C, otherwise some impurities, such as Sb2O3 and unreacted Se, would exist in the final products. In addition, the role of hydrazine, which serves as both the reducing agent and the coordinator, was also found to be crucial for the formation of the rod-like products. The resulted products were characterized by XRD, TEM, XPS, UV-vis adsorption spectroscopy and Raman spectroscopy.

Email: ydli@tsinghua.edu.cn Tel.: +86-10-62772350 Fax: +86-10-62788765 .
Time Period TuP Sessions | Topic SS Sessions | Time Periods | Topics | AVS2001 Schedule