Strain enhancement for a MoS<sub>2</sub>-on-GaN photodetector with an Al<sub>2</sub>O<sub>3</sub> stress liner grown by atomic layer deposition
Zhiwen Li, Jiangliu Luo, Shengqun Hu, Qiang Liu, Wenjie Yu, Youming Lu, Xinke Liu
Abstract
Strain regulation as an effective way to enhance the photoelectric properties of two-dimensional (2D) transition metal dichalcogenides has been widely employed to improve the performance of photovoltaic devices. In this work, tensile strain was introduced in multilayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>MoS</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> grown on GaN by depositing 3 nm of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:msub> <mml:mi>Al</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> on the surface. The temperature-dependent Raman spectrum shows that the thermal stability of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>MoS</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> is improved by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:msub> <mml:mi>Al</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> . Theoretical simulations confirmed the existence of tensile strain on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>MoS</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> covered with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"> <mml:mrow> <mml:msub> <mml:mi>Al</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> , and the bandgap and electron effective mass of six layers of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m7"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>MoS</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> decreased due to tensile strain, which resulted in an increase of electron mobility. Due to the tensile strain effect, the photodetector with the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m8"> <mml:mrow> <mml:msub> <mml:mi>Al</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> stress liner achieved better performance under the illumination of 365 nm wavelength, including a higher responsivity of 24.6 A/W, photoconductive gain of 520, and external quantum efficiency of 8381%, which are more than twice the corresponding values of photodetectors without <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m9"> <mml:mrow> <mml:msub> <mml:mi>Al</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> . Our work provides an effective technical way for improving the performance of 2D material photodetectors.