Systematic study of methanol addition to enhance the film development of APCVD tin oxide
- PDF / 156,085 Bytes
- 4 Pages / 432 x 648 pts Page_size
- 100 Downloads / 137 Views
Systematic study of methanol addition to enhance the film development of APCVD tin oxide Joop van Deelen*1, Ioanna Volintiru, Paul Poodt1 1 Netherlands Organization for Applied Scientific Research (TNO), PO Box 6235, 5600 HE Eindhoven, The Netherlands, *corresponding author: [email protected] ABSTRACT Undoped tin oxide (SnO2) thin films have been deposited in a stagnant point flow chemical vapor deposition reactor. By adding methanol during the deposition process ten times more conductive SnO2 films are obtained, with remarkably high mobility values of up to 55 cm2/Vs. The investigations on the morphological and structural properties indicate that the main effect of methanol is the densification of the SnO2 films, which probably causes the improvement in the electrical properties. In all conditions the nucleation and coalescence phases take place very early in the growth. The films are already very conductive at a thickness below 10 nm, which is very beneficial to applications that have strict requirements in terms of film transparency. This high conductivity was attributed to a high carrier concentration, obtained without intentional doping. INTRODUCTION One of the most commonly used Transparent Conductive Oxides (TCOs) is tin oxide (SnO2), a wide band gap semiconductor (3.6 eV). It has been successfully implemented in various fields of application, such as energy-efficient windows [1] and thin-film solar cells [2]. For each of these applications, specific requirements for the film electrical, optical, morphological and structural properties apply. These properties are dependent on many (deposition) parameters. For applications where transparency is a critical parameter, such as solar cells, obtaining high conductivity through a high electron mobility is preferred over a high electron concentration. The film thickness is also an important parameter. Many studies show that the electrical and morphological properties of TCO films are highly dependent on the thickness [3]. Moreover, obtaining TCO films as thin as possible with the same electrical properties is desired due to their higher transparency and lower fabrication costs. Alcohols are sometimes mentioned as additives in (AP)CVD of SnO2 in order to improve the film electrical properties. However, to the best of our knowledge, only a few articles have reported on the influence of alcohols on the SnO2 film growth [4,5]. The exact mechanism behind these improvements is therefore still largely unknown. The main conclusion is that the addition of alcohols appears to improve both the initial film formation (in the nucleation stage), as well as the subsequent bulk film electrical, structural and morphological properties. This work refers to as-grown undoped SnO2 thin films obtained from TTC and H2O in an APCVD stagnant point flow reactor. By changing the exposure time of the substrate to the gases, SnO2 samples with various thicknesses were obtained.
71
RESULTS The development of the electrical properties of SnO2 with increasing layer thickness, deposited with a
Data Loading...
