Timo Asikainen

Growth of In2S3 thin films by atomic layer epitaxy

In2S3 films were deposited by ALE using InCl3 and H2S as precursors. The films were characterized by means of XRD, RBS, SEM and by optical and electrical measurements. The highest growth rate obtained was 1.4 A/cycle at 300°C. The films were polycrystalline β-In2S3 having a band gap of 2.3 eV.

Effects of intermediate zinc pulses on properties of TiN and NbN films deposited by atomic layer epitaxy

The reasons for the improvements gained by using intermediate zinc pulses in atomic layer epitaxy growth of TiN and NbN films were examined by a comprehensive characterization and comparison of films prepared from TiCl4 or NbCl5 and NH3 with and without zinc. The characterization techniques used comprise time-of-flight elastic recoil detection analysis, secondary ion mass spectrometry, Rutherford backscattering spectrometry, nuclear resonance broadening, proton backscattering spectrometry, deuteron induced reactions, proton induced X-ray emission, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and Hall effect and reflectance measurements. The effect of zinc was found to be manifold: both compositional and structural changes were observed. In the case of TiN the major improvement gained by using zinc was significantly decreased oxygen contamination whereas a marked increase of grain size was the dominant effect observed with NbN. A clear correlation between the compositional and structural changes and the improvements of the electrical properties was established.

Growth of In[sub 2]O[sub 3] thin films by atomic layer epitaxy

Simultaneously occurring transparency and electrical conductivity give rise to numerous thin film applications for indium oxide doped with tin (ITO), e.g., as transparent electrodes in flat panel displays and electrochromic windows, as active and passive components in photovoltaic devices, and as long wavelength IR radiation reflecting heat mirror layers in energy saving windows. Indium oxide thin films were deposited by atomic layer epitaxy technique at 400 and 500 C using InCl[sub 3] and water as reactants. The films were characterized by means of X-ray diffraction, Rutherford backscattering spectrometry, nuclear reaction analysis, scanning electron microscopy, and by optical and electrical measurements. The highest deposition rate obtained was only 0.27 [angstrom]/cycle. The films were polycrystalline In[sub 2]O[sub 3] having the [100] direction as the most pronounced orientation. The resistivities of the highly transparent films were in the order of 3 [times] 10[sup [minus]3] [Omega]-cm.

Growth of Indium‐Tin‐Oxide Thin Films by Atomic Layer Epitaxy

Transparent and conducting indium-tin-oxide (ITO) finds use in numerous thin-film applications, e.g., as transparent electrodes in flat panel displays and electrochromic windows, as active and passive components in photovoltaic devices, and as long infrared wavelength (IR) radiation reflecting heat mirror layers in energy efficient windows. Indium-tin-oxide thin films were deposited by atomic layer epitaxy at 500 C using InCl{sub 3}, SnCl{sub 4}, and water as precursors. The films were characterized by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, polarography, and by optical and electrical measurements. The films had polycrystalline In{sub 2}O{sub 3} structure. In addition, the SnO{sub 2} phase was detected in films containing the highest tin contents. High transparencies and resistivities in the order of 2.4{times}10{sup {minus}4} {Omega}cm could be achieved by optimizing the tin doping procedure. Postannealing decreased the resistivity about 5%.

ENHANCED GROWTH RATE IN ATOMIC LAYER EPITAXY OF INDIUM OXIDE AND INDIUM-TIN OXIDE THIN FILMS

Growth rates of and (ITO) films were increased by substituting water with hydrogen peroxide in the atomic layer epitaxy processes where and served as metal precursors. The growth rate of increased from /cycle, and that of ITO from /cycle. By optimizing the pulse and purge times the overall deposition rate could be increased further, from , for grown at . Film properties, such as high conductivity and transmittance, remained the same for the two oxygen precursors. ©1998 The Electrochemical Society

ALE growth of transparent conductors

Owing to its self-limiting growth mechanism the Atomic Layer Epitaxy (ALE) technique is capable of growing uniform high quality thin films on large area substrates. Therefore, ALE is an attractive choice for depositing transparent electrically conducting films for large area applications, such as solar cells and flat panel displays. In this paper studies on ALE growth of In{sub 2}O{sub 3} and ZnO based transparent conducting thin films will be presented. In{sub 2}O{sub 3}, In{sub 2}O{sub 3}:Sn and In{sub 2}O{sub 3}:F films were grown at 500 C and their lowest resistivities were about 3 {times} 10{sup {minus}3}, 2 {times} 10{sup {minus}4} and 6 {times} 10{sup {minus}4} {Omega}cm, respectively. Low temperature (120--350 C) ALE deposition processes were developed for ZnO and ZnO:Al films, the latter having resistivities as low as 8 {times} 10{sup {minus}4} {Omega}cm. A straightforward scale-up of the ZnO process from 5 x 5 to 30 x 30 cm{sup 2} substrate size was also demonstrated.

AFM and STM studies on In2O3 and ITO thin films deposited by atomic layer epitaxy

Abstract The surface morphology of In2O3 and In2O3:Sn (ITO) thin films deposited by atomic layer epitaxy has been studied by AFM and STM. The effects of film thickness, tin content and different doping schemes on the surface morphology were examined. Also the initial growth of SnO2 was studied in order to better understand the influence of the intermediate SnO2 pulses. Increasing film thickness led to increasing surface roughness, but the roughening rate decreased substantially after about 800 deposition cycles. In the ITO films the dependencies of roughness and electrical resistivity on the tin content were found to be parallel, both having a minimum at a tin content of about 4–7%. Deposition of a few cycles of SnO2 on a rough In2O3 film surface was found to decrease the surface roughness. In addition to the studies on the morphological development of the films, comparison between AFM and STM data allowed to obtain information on the electrical properties of the films.

Modifying ALE grown In2O3 films by benzoyl fluoride pulses

Indium oxide thin films grown at 500°C by atomic layer epitaxy from InCl3 and water were modified by benzoyl fluoride pulses. A broad minimum in resistivity was found when the number of the benzoyl fluoride containing cycles were 6–15% of total. The lowest resistivities were 4–5×10−4 Ωcm. Fluorine contents studied by nuclear resonance broadening method were below 0.02 at% in all the films, which is far too low to explain the measured carrier concentrations 2–3×1020 cm−3. This leads to an assumption that rather than acting as a fluorine source, the benzoyl fluoride modifies the In2O3 structure creating additional oxygen vacancies which serve as sources of the charge carriers. The films had cubic In2O3 structure and optical transparencies over 90%.

Fluorine implantation of atomic layer epitaxy grown In{sub 2}O{sub 3} films

In{sub 2}O{sub 3} films grown by atomic layer epitaxy were implanted by fluorine ions with doses ranging from 5 {times} 10{sup 14} to 1.4 {times} 10{sup 17} ions/cm{sup 2}. Annealing at 500 C decreased the fluorine contents by {approximately}40%, as analyzed by the nuclear resonance broadening method. The lowest resistivity, 2.7 {times} 10{sup {minus}4} {Omega} cm, was measured from film having an average fluorine content of 2.3 atom percent. Hall mobilities of the In{sub 2}O{sub 3}:F films were in the same range as those of the undoped In{sub 2}O{sub 3}, i.e., 60 to 80 cm{sup 2}/Vs.