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W. Bala1‘2 K. Paprocki1, M. Kuczkowska1, P. Popielarski1, K. Fabisiak1, A. Korcala2, K. Banach2, Ł. Borszewski2,
1Institute ofPhysics, Kazimierz Wielki University, Powstańców Wielkopolskich 2, PL 85-072
Toruń, Poland wbala @fizyka, umk.pl
Institute ofPhysics, N. Copernicus University, Grudziądzka 5/7, PL 87-100 Toruń, Poland
During the last years polymers based on carbazołe such as polycarbazole, poly(vinyl carbazole) (PVK) and poly(N-vinyl carbazole) and polycarbonate have attracted considerable attention due to their interesting physical properties followed by various technological applications in the area of electronics and optoelectronics [1-3].
The carbazole family forms a subset of the organie materials under study for blue organie light emitting diodes (OLED) and photovoltaic cells (PC) applications
A very promising family of materials that belongs to this category is the polycarbonate. Their good sensitivity to the solar spectrum combined with the high thermal, chemical and photochemical stability as well as their Iow cost makes polycarbonate derivatives strong candidates for futurę device applications especially in the area of photovoltaics (PV) where large area and cost-effective solar cells are reąuired. Over the past 20 years, polycarbonate based and a more generał organie PV celi has been the object of intense research efforts in numerous academic and industrial research laboratories. However, a very limited amount of information is available in scientific literaturę about the electrical properties of polycarbonate thin layers, especially as a function of temperaturę.
In this paper, we use the simple dip-coating techniąue to fabricate the polymer-based Schottky diodę. The polycarbonate layered structureswere fabricated on high-quality (1 0 0)-orientedn-type silicon and ąuartz substrates. We have investigated the optical and electrical properties of polycarbonate thin films deposited on silicon and ąuartz substrates by dip-coating method. The photoluminescence (PL), transmission (T) and reflection (R) spectra, current-voltage (I-V), capacitance-voltage (C-V) and charge deep-level transient spectroscopy (Q-DLTS) measurements have been made in the temperaturę rangę 100K-350K.
To explain their electrical behavior, the charge transport mechanism in organie semiconductor materials is a controversial topie, and no unified theory is available to explain the experimental results under different conditions to an acceptabłe degree of aceuracy [4]. We present a new method to extract the correct electrical characteristics in which the effects of the series resistance and the ideality factor have been taken into account. The method is based on the modified Norde function method combined with the conventional forward I-V method.
[1] D. Romero, M.Schaer, M. Leclerc, D. Ades, A. Siove, and Z. Zuppiroli, Synth. Met., 80, p. 271, 1996. [2] C. Chao and S. Chen Appl. Phys. Lett., vol. 73, p. 426, 1998.
[3] H. Meng, Z. Chen, W. Yu, J. Pei, X. Liu, Y. Lai, and W. Huang Synth. Met.,vól. 100, p. 297, 1999. [4] A. Chempbell, D. Bradley, and D. Lidzey, J. Appl. Phys., vol. 82,pp. 6326-6342, 1997.
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W. Bala1‘2 K. Paprocki1, M. Kuczkowska1, P. Popielarski1, K. Fabisiak1, A. Korcala2
‘institute ofPhysics, Kazimierz Wielki University, Powstańców Wielkopolskich 2, PL 85-072
Toruń, Poland wbala @fizyka, umk.pl
Institute ofPhysics, N. Copernicus University, Grudziądzka 5/7, PL 87-100 Toruń, Poland
Diamond exhibits outstanding semiconductor properties with a wide band gap which is indispensable for use in electronic devices such as high temperaturę transistors and blue light-emitting diodes. One of the key problems in diamond devices fabrication is the doping of electrically active n and p-type doped atoms into diamond produced by CYD. Changes of conductance and capacitance at different frequencies, polarization and temperatures have been observed. The diamond layers deposited by HF CVD are supposed to contain a large amount of defects at present stage of synthesis what would provide an important obstacle if this materiał is used for electronics applications.
This paper considers an AC/DC electrical features and the growth of [100]-oriented diamond film prepared on (001) Si substrates by HFCVD method. SEM and Raman measurements indicated that high ąuality polycrystalline diamond films with [100]-faced structure were obtained. We reported investigation of Al/diamond film/Si/Al heterostructure through current-voltage I (V), conductance- and capacitance- freąuency dependencies (G(f),C(f)) at various temperatures (Thermal Admittance Spectroscopy TAS) The diamond films used in this experiment were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor at the pressure of 100 mbar. The flow rate of the hydrogen gas was 100 sccm (standard cubic centimeter per minutę), flow of the nitrogen was about lsccm and that of acetylene was 10 sccm. As substrate n-type silicon wafer of the [100] orientation was used. Before diamond deposition the surface of the substrate was polished with 0,01 mm diamond pastę in order to increase the density of nucleation. During diamond layer growth the substrate temperaturę was heldat800°C.
Measurements were performed in the freąuency rangę from 50Hz to 250kHz. Thermal admittance spectroscopy (TAS) curves have been measured in the temperaturę rangę from 100K to 300K. An equivalent circuit of the structure was proposed. It was found for the samples doped with nitrogen, that incorporated doped atoms induce some levełs of electrically active defects with activation energies at the 0.36 , 0.29 and 0.25 eV. The naturę of observed defects and differences between trapping centres in HFCYD diamond films are discussed.
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A. Bratkowski1, W. Bala1‘2
In recent decade sińce the moment when the visible photoluminescence at room temperaturę in porous silicon reported in 1990 by Canham [1], beginning significant interest of this materiał. Porous silicon has been very attractive materiał for production of photovoltaic devices [2], photodetectors [3] and light emitting diodes [1] due to optical properties and lower cost of product. At the presence researches are concentrated on use porous silicon for production of gas sensor [4,5] and as matrix for immobilization of a variety of biomolecular complexes, DNA fragments and antibodies [6,7]sińce of its extremely large surface.
The study of the transport properties of thin porous silicon films, necessary for the solar celi and sensor applications, has focused much attention. The density of states in the band gap of porous silicon influences strongly these properties and conseąuently the device performance. These band gap states arise from oxygen vacancies and surface states due to adsorbed oxygen. The observed long relaxation times and charging effects indicate that there is a large number of surface defects. They act as traps and affect both carrier’s mobility and recombination.
The porous silicon samples were prepared by electrochemical etching of p-type epitaxial layer deposited on Iow resistivity p+ substrate. As an electrolyte the HF acid diluted in isopropyl alcohol and current density of 10 mA/crm were used in this method. Metal contacts (Al) circle shape on the surface of sample and contact (Al) on the Si background were prepared by thermally deposition method. Photovoltage curves have been measured at wavelength rangę of 500 nm - 1150 nm in different gas atmospheres and in different gas concentrations. The output light was chopped 80 Hz freąuency with duration of light on the sample surface 2,2 ms in each cycle. The electrical field 1,25 V/|im was applied to the sample in the forward direction. Experimental results of photovoltage have been used to compare photovoltage spectra.. Intensity changes of photovoltage curves in different gas concentration have been observed.
The value of dark conductivity in vacuum (10-2 Pa) was found more than two orders of magnitude higher than that in air. Vacuum creates oxygen vacancies and releases free electrons from the bulk, making the film more conductive. On the other hand air atmosphere causes the adsorption of oxygen molecules and creates O2” surface states by removing electrons from the bulk and the conduction band, causing a decrease in the film conductivity.
[1] L.T. Cahnam, Appl. Phys. Lett, vol. 57, pp. 1046, 1990
[2] I. A. Levitsky, W. B. Euler, N. Tokranova, B. Xu, J. Castracane, Appl. Phys. Lett., vol. 85, pp. 6245, 2004 [3] A. M. Rossi, H. G. Bohn, Phys, Stat. Sol. (a), vol 202, pp .1644, 2005
[4] Z. Gaburro, P. Bettotti, M. Saiani, L. Pavesi, L. Pancheri, C. J. Oton, N. Capuj, Appl. Phys. Lett., vol. 85, pp. 555, 2004
[5] Z.H. Mkhitaryan, A.A. Shatveryan, V.M. Aroutiounian, M. Ghulinyan, L. Pavesi, L.B. Kish, CG. Graoqvist, PhysicaE, vol. 38, pp. 160, 2007
[6] D.C. Tessier, S. Boughaba, M. Arbour, P. Roos, G. Pan, Sensors and Actuators B, vol. 120, pp. 220, 2006 [7] L. Stefano, P. Arcari, A. Lamberti, C. Sanges, L. Rotiroti, I. Rea, I. Rendina, Sensors, vol. 7, pp. 214, 2007
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W. Bala1‘2 K. Paprocki1, M. Kuczkowska1, K. Fabisiak1, A. Zawadzka2, P. Płóciennik2, J. Szatkowski2, K. Banach2, J. Luc3, B. Sahraoui3,
1lnstitute ofPhysics, Kazimierz Wielki University, Powstańców Wielkopolskich 2, PL 85-072 Bydgoszcz, Poland wbala@fizyka, umk.pl
Institute ofPhysics, N. Copernicus University, Grudziądzka 5/7, PL 87-100 Toruń, Poland
3Laboratory POMA, UMR CNRS 6136, University ofAngers, 2 Boulevard Lavoisier, 49045 Angers, France,
Zinc oxide (ZnO) thin films have attracted significant attention as a wide gap semiconductor due to their wide rangę of electrical and optical properties. It is a wide-bandgap oxide semiconductor with a direct energy gap of about 3.37eV and a larger exciton binding energy (60 meV), which assures more efficient exciton emissions at higher temperatures. The thin layers of ZnO have potential application in electronics, optoelectronics and information technology devices including displays, sołar cells and sensors [1,2].
The optical properties of ZnO thin films grown by sol-gel method on silica glass were studied using second and third harmonie generation and photoluminescence measurements, respectively. The structural properties of the ZnO thin films were carried out using x-ray method. The effects of the thickness variation and annealing temperaturę on the crystallinity parameters were observed. The strong dependence of the films structure, the crystalline ąuality and the optical properties was also noticed. We observed that the annealing of ZnO films leads to inerease of the crystallite size and this cause to considerable rise of the photoluminescence intensity. The photoluminescence spectra were measured at the temperaturę rangę from 13 K to 350 K. We observed the changing of the near band edge (NBE) emission with temperaturę.
The very high conversion efficiency to the second and third harmonie radiations are achieved for Q-switched Nd:YAG laser working at 1064 nm.
[1] S. Bandyopadhyay, G.K. Paul, S.K. Sen, Sol. Energy Mater. Sol. Cells 71 (2002) 103. [2] Y. Natsume, H. Sakata, Thin Solid Films 372 (2000) 30.
