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Research Papers

# Material Development for Improved $1eV$$(GaIn)(NAs)$ Solar Cell Structures

[+] Author and Article Information
K. Volz

Material Sciences Center and Department of Physics, Philipps University, D-35032 Marburg, Germanykerstin.volz@physik.uni-marburg.de

T. Torunski, D. Lackner, O. Rubel, W. Stolz

Material Sciences Center and Department of Physics, Philipps University, D-35032 Marburg, Germany

C. Baur, S. Müller, F. Dimroth, A. W. Bett

Fraunhofer Institute for Solar Energy Systems, D-79110 Freiburg, Germany

J. Sol. Energy Eng 129(3), 266-271 (Oct 23, 2006) (6 pages) doi:10.1115/1.2734568 History: Received November 10, 2005; Revised October 23, 2006

## Abstract

The dilute nitride $(GaIn)(NAs)$ material system grown lattice matched to $GaAs$ or Ge with a $1eV$ band gap is an interesting material for the use in four-junction solar cells with increased efficiencies. As a result of its metastability, several challenges exist for this material system, which up to now limits the device performance. We performed nanostructural analysis in combination with photoluminescence characterization to optimize the metal organic vapor phase growth as well as the annealing conditions for the quaternary solar cell material. The optimum annealing conditions depend strongly on the In content of the quaternary material. Valence force field calculations of stable N environments in the alloy support the model that the N moves from a Ga rich environment realized during growth into an In rich environment upon annealing. Simultaneously, N induced strain fluctuations, which are detected in the N containing material upon growth, are dissolved and the device properties are improved.

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## Figures

Figure 1

Cross-sectional TEM dark field images of a (Ga0.92In0.08)(N0.03As0.97) solar cell structure (a) as grown, using the (002) reflection; (b) as grown, using the (202) reflection; (c) annealed, using the (202) reflection; and (d) plan view TEM dark field micrograph of (GaIn)(NAs) using g=(202)

Figure 2

Cross-section TEM dark field images of a (Ga0.7In0.3)(N0.015As0.985) quantum well using g=(202) before (a) and after (b) annealing

Figure 3

Ball and stick models of different N configurations in Ga(NAs) and (GaIn)(NAs): (a)N nearest neighbor in [110] direction; (b)N in a 3Ga 1 In configuration; and (c)N chain, oriented in [001] direction

Figure 4

Probability for different In nearest neighbor environments of nitrogen depending on the In content in the quaternary material

Figure 5

Room temperature photoluminescence spectra of a (Ga0.92In0.08)(N0.03As0.97) solar cell structure annealed under different conditions

Figure 6

DLTS measurements: (a) TEGa as grown and annealed and (b) TMGa as grown and annealed

Figure 7

IQE of a (GaIn)(NAs) pin solar cell structure

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