Paper AS-TuP18
Atom Probe Tomography Analysis of Grain Boundaries in CdTe
Tuesday, October 30, 2012, 6:00 pm, Room Central Hall
| Session: |
Applied Surface Science Poster Session |
| Presenter: |
V.S. Smentkowski, General Electric Global Research Center |
| Authors: |
V.S. Smentkowski, General Electric Global Research Center
D.J. Larson, Cameca Instruments Inc.
D.A. Reinhard, Cameca Instruments Inc.
T.J. Prosa, Cameca Instruments Inc.
D. Olson, Cambridge University, UK
D. Lawrence, Cameca Instruments Inc.
P.H. Clifton, Cameca Instruments Inc.
R.M. Ulfig, Cameca Instruments Inc.
T.F. Kelly, Cameca Instruments Inc.
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| Correspondent: |
Click to Email |
Photovoltaic materials convert photons to electrical energy (e.g., solar cells) or convert electrical energy into light (e.g. light emitting diodes). Films based on the II-VI compound CdTe are currently regarded as one of the leading type II materials for development of cost-effective solar cells as the CdTe band gap is near ideal for photovoltaic conversion efficiency [1]. While theoretical efficiency values approach 30% [2], commercial and laboratory tests of CdS/CdTe heterojunctions range from ~10% to ~17%, respectively [3,4]. The presence of grain boundaries in these structures likely plays an important role in the observed efficiency. In the current work we investigate, for the first time, the applicability of atom probe tomography (APT) to characterize grain boundaries within the CdTe layer of a solar device. APT data were collected on a Cameca LEAPTM 4000X HR operated at a base temperature of 40K with a laser energy of 3pJ, a repetition rate of 100kHz and an ion detection rate of 1%. Specimens for APT were prepared by standard focused-ion-beam milling methods [5] from a CdTe layer within a solar cell. Laser-pulsed APT spectra from CdTe-based alloys are quite complex [6,7]. There are two reasons for this: 1) Cd and Te each have eight isotopes and 2) Cd and Te field evaporate in a multitude of complex molecular ions species. The following ions were detected in mass spectra: Cd+, Te+, CdTe++, Cd2++, and Te2++, Cd2Te++ and CdTe2++, Cd2+, CdTe+ and Te2+. In spite of the complex nature of these spectra, all of the peaks are identifiable as some combination of Cd and/or Te. This poster will show both the measured spectra and CdTe composition estimate, as well as 3D images revealing enhancement of S and Cl at a grain boundary.
References
[1]. Z. Fang et al., International Journal of Photoenergy 2011 (2011) 297350.
[2]. A. Bosio et al., Progress in Crystal Growth and Characterization of Materials 52 (2006) 247.
[3]. M. Powalla & D. Bonnet, Advances in OptoElectronics 2007 (2007) 97545.
[4]. http://investor.firstsolar.com/releasedetail.cfm?ReleaseID=639463
[5]. D.J. Larson et al., Ultramicroscopy, 79 (1999) 287, M.K. Miller et al., Micro. Microanal., 13 (2007) 428.
[6]. P. P. Choi et al., Microscopy Today, 20 (2012) 18.
[7]. D. J. Larson et al., Microscopy and Microanalysis (2012), in press.