Carrier dynamics of Mn-induced states in GaN thin films

Yu-Ting Chen,Jinn-Kong Sheu,Po-Cheng Chen,Chi-Yuan Yang,Kung-Hsuan Lin

doi:10.1038/s41598-017-06316-7

Yu-Ting Chen, Jinn-Kong Sheu + Show 3 more

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https://doi.org/10.1038/s41598-017-06316-7

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Abstract

GaN-based materials are widely used for light emission devices, but the intrinsic property of wide bandgap makes it improper for photovoltaic applications. Recently, manganese was doped into GaN for absorption of visible light, and the conversion efficiency of GaN-based solar cells has been greatly improved. We conducted transient optical measurements to study the carrier dynamics of Mn-doped GaN. The lifetime of carriers in the Mn-related intermediate bands (at 1.5 eV above the valence band edge) is around 1.7 ns. The carrier relaxation within the Mn-induced bandtail states was on the order of a few hundred picoseconds. The relaxation times of different states are important parameters for optimization of conversion efficiency for intermediate-band solar cells.

Highlights

GaN-based materials are widely used for light emission devices, but the intrinsic property of wide bandgap makes it improper for photovoltaic applications
Manganese was doped into GaN to induce extra states for absorption of visible light, and the conversion efficiency of solar cells based on Mn-doped GaN was greatly improved[22,23,24,25]
The un-doped GaN was treated as the sample for control measurement because Mn intermediate band (IB) states in Fig. 2(b) should not exist in un-doped GaN

Summary

Introduction

GaN-based materials are widely used for light emission devices, but the intrinsic property of wide bandgap makes it improper for photovoltaic applications. Manganese was doped into GaN for absorption of visible light, and the conversion efficiency of GaN-based solar cells has been greatly improved. Luque and Marti proposed that the conversion efficiency of solar cells could increase by intermediate band (IB) within the bandgap of the material[10]. Manganese was doped into GaN to induce extra states for absorption of visible light, and the conversion efficiency of solar cells based on Mn-doped GaN was greatly improved[22,23,24,25]. The transmission spectra of Mn-doped GaN with concentrations of 1.1 × 1019 cm−3 and 1.2 × 1020 cm−3 are shown in red and blue curves, respectively They reveal strong dependence on the concentration of Mn. The absorption bands, centered at 820 nm (1.5 eV) and www.nature.com/scientificreports/. The absorption band, centered at 1.5 eV, is termed as Mn IB

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