Pulsed Laser Deposition of Cadmium Stannate, a Spinel-Type Transparent Conducting Oxide
- PDF / 389,960 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 59 Downloads / 193 Views
ABSTRACT We present the first report of the synthesis of Cd 2 SnO 4 films by pulsed laser deposition. Controlling the substrate temperature and the ambient atmosphere allowed for the synthesis of films ranging from amorphous to crystalline with some crystalline films exhibiting strong texture. Highly transparent films with large mobilities were obtained for both the amorphous 2 and crystalline films. Sheet resistances of 15.5 92/square and mobilities of up to 44.7 cm /V.s were observed. Typical carrier concentrations showed the crystalline films to be degenerate 3 with carrier concentrations of 5 x 1020 cm- while amorphous films had carrier concentrations lower by about half. Band gaps for the films ranged between 3.1-3.8 eV. These films are attractive candidates for TCO applications in thin film photovoltaic devices, flat panel displays, electrochromic windows, and as plasma filters for thermophotovoltaic devices.
INTRODUCTION Transparent conducting oxides (TCO) are vital to a number of key new technologies. In photovoltaic (PV) cells and flat panel displays, TCOs act as a transparent electrical contact. Building glazing applications such as electrochromic windows and heat mirrors use TCOs as critical elements. Thermophotovoltaic (TPV) applications can utilize TCOs as an infrared (plasma) filter which allows usable radiation to pass through to the cell and reflects the unusable radiation back to the source thereby increasing energy efficiency. The dominant design criteria for most TCO applications are high transparency in the visible range, high conductivity, high mobility, and a plasma edge near 3 gim. A material with a band gap of 3.0 -3.5 eV will be transparent to light from 350-400 nm to its plasma edge which is suitable for most solar cell and flat panel applications. In thermophotovoltaic (TPV) cells, the position of the plasma edge is crucial for the proper filtering of the heat radiation. Cubic spinel Cd 2 SnO 4 is a TCO which has a small effective mass and a typical range of carrier concentrations from 1018 to 1020 cm- 3 resulting in a plasma edge suitable for TPV applications. Cadmium stannate has been studied in the past using numerous deposition 2 techniques.1, To the best of our knowledge, this paper reports the first Cd 2 SnO 4 thin films grown by pulsed laser deposition (PLD). Our films exhibit outstanding transparency, mobility, and resistivity making Cd 2SnO 4 films and derivatives thereof suitable toward a wide range of applications.
EXPERIMENTAL Equipment The PLD system used for the deposition of Cd 2 SnO 4 films consists of a 5-cross 6" diameter sphere. A turbo pump backed by a mechanical pump evacuates the system to a base pressure 500°C were crystalline with the cubic spinel structure.
52
~(222)
"• er4•
S(111)(511) S(311)
(333 0
(220)
4. 0-
(440) Ox550 (533)
(422)
S-Ox500b
"•
k 10Ox400
•
•'• --
10
20
•
•Ox500a
25N500
40
30
50
60
70
0/20 (degrees) Figure 1. XRD 0/20 data for the Cd 2SnO 4 films by PLD. Films Ox25 and N500 show amorphous patterns, Ox400 shows little
Data Loading...
