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A significant improvement in the quality of dilute nitrides has recently led to the ability to reveal depletion widths in excess of 1 μm at 1 eV [1]. The real viability of dilute nitrides for PV has been recently demonstrated with the reporting of a record efficiency of 43.5% from a 4J MJSC including GaInNAs(Sb) [2]. Despite the progress made, these materials remain poorly understood and work continues to improve their lifetime and reproducibility.
We have investigated the possibility of improving the functionality of GaInNAs using hydrogenation to selectively passivate mid-gap defects, while preserving the substitutional nitrogen. Temperature dependent photoluminescence measurements of the intrinsic region of a GaInNAs p-i-n solar cell show a classic “s-shape” associated with localization prior to hydrogenation. No sign of this “s-shape” is evident after hydrogenation, despite the retention of substitutional nitrogen as evidenced by the band absorption of 1 eV. The absence of an “s-shape” at low-temperature in hydrogenated GaInNAs is rather curious since, even in high quality nitrides this behavior is due to the emission of isoelectronic centers created via N-As substitution [3]. The potential origins of this behavior will be discussed. The promise of this process for GaInNAs solar cells was demonstrated by a three-fold improvement in the performance of a hydrogenated device with respect to an as-grown reference [4].
[1] “Wide-depletion width GaInNAs solar cells by thermal annealing,” I. R. Sellers, W-S. Tan, K. Smith, S. Hooper, S. Day and M. Kauer, Applied Physics Letters 99, 151111 (2011)
[2] “43.5% efficient lattice matched solar cells,” M. Wiemer, V. Sabnis, and H. Yuen, Proc. SPIE 8108, 810804 (2011)
[3]“Probing the nature of carrier localization in GaInNAs, epilayers using optical methods,” T. Ysai, B. Barman, T. Scarce, G. Lindberg, M. Fukuda, V. R. Whiteside, J. C. Keay, M. B. Johnson, I. R. Sellers, M. Al Khalfioui, M. Leroux, B. A. Weinstein and A. Petrou. Applied Physics Letters 103, 012104 (2013)
[4] “Improved performance in GaInNAs solar cells by hydrogen passivation by hydrogen passivation,” M. Fukuda, V. R. Whiteside, J. C. Keay, A. Meleco, I. R. Sellers, K. Hossain, T. D. Golding, M. Leroux, and M. Al Khalfioui, Applied Physics Letters 106, 141904 (2015)
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