4.6 Article

Single- and dual-wavelength photodetectors with MgZnO/ZnO metal-semiconductor-metal structure by varying the bias voltage

Journal

NANOTECHNOLOGY
Volume 27, Issue 37, Pages -

Publisher

IOP PUBLISHING LTD
DOI: 10.1088/0957-4484/27/37/375502

Keywords

metal-semiconductor-metal; photodetector; dual wavelength; MgxZn1-xO/ZnO; piezoelectric polarization

Funding

  1. National Science Council of the Republic of China, Taiwan [NSC 102-2112-M-415-004-MY3]

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By varying the bias voltage of an MgxZn1-xOO/ZnO metal-semiconductor-metal photodetector (MSM-PDs), the detection wavelength can be modulated from a single to a dual wavelength. A long-wavelength band response is caused by the ZnO absorption and a short-wavelength band response is caused by MgxZn1-xO. At a 0 V bias voltage, the photogenerated electrons in ZnO are confined to the MgxZn1-xO/ZnO interface, arising from the piezoelectric polarization. The accumulated electrons hop the MgxZn1-xOO layer through the assistance of defects; however, the photogenerated electrons in MgxZn1-xOO cannot cross over the large barrier height at the Au/ MgZnO interface, resulting in a single-wavelength photodetector with a long-wavelength band (345-400 nm) having a peak wavelength of 370 nm. By increasing the bias voltage to 1-2 V, the barrier height is lowered, enabling the photogenerated electrons in MgxZn1-xOO to easily cross over the low barrier height, leading to dual-wavelength photodetectors having peak wavelengths of 370 and 340 nm. On further increasing the bias voltage beyond 2 V, the photogenerated electrons in ZnO sink deeply in the hollow at the MgxZn1-xOO/ZnO interface owing to the large applied voltage. These electrons are effectively confined at the MgxZn1-xOO/ZnO interface, which retards the tunneling of the photogenerated electrons in ZnO through the MgxZn1-xOO layer; hence the MSM-PDs revert back to single wavelength photodetectors; however, the detection wavelength is different from that of the MSM-PDs biased at 0 V. Instead of having a long-wavelength band (345-400 nm), the MSM-PDs demonstrate a short-wavelength band (320-345 nm) at a 3 V bias voltage.

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