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Ultraviolet photodetectors based on ZnO nanorods-seed layer effect and metal oxide modifying layer effect.

Zhou H, Fang G, Liu N, Zhao X - Nanoscale Res Lett (2011)

Bottom Line: In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively.For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (Dλ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism.Also the ratio of D254* to D546* was calculated above 8 × 102 for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electronic Science and Technology and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, People's Republic of China. gjfang@whu.edu.cn.

ABSTRACT
Pt/ZnO nanorod (NR) and Pt/modified ZnO NR Schottky barrier ultraviolet (UV) photodetectors (PDs) were prepared with different seed layers and metal oxide modifying layer materials. In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively. For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (Dλ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism. Also the ratio of D254* to D546* was calculated above 8 × 102 for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.

No MeSH data available.


Carrier transport processes in the ZnO NRs PDs. (a) Photogenerated electron transport route under UV illumination. (b) Schematic energy level diagrams of the PD with MgZnO seed layer at dark and under UV illumination, respectively.
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Figure 6: Carrier transport processes in the ZnO NRs PDs. (a) Photogenerated electron transport route under UV illumination. (b) Schematic energy level diagrams of the PD with MgZnO seed layer at dark and under UV illumination, respectively.

Mentions: In order to explore the enhanced performance of PDs with MgZnO seed layer, carrier transport processes in the ZnO NRs PDs under forward bias are illustrated in Figure 6a. In the dark, oxygen is adsorbed at the surface of the NRs to form a chemically adsorbed surface state. Under UV illumination, electron-hole pairs are generated when photon energy exceeds the energy band gap (hυ >Eg). Photogenerated holes move to the surface of ZnO NRs and the adsorbed oxygen is photodesorbed, and unpaired electrons in the NRs migrate to the electrodes at a bias voltage and contribute to the photocurrent [6,12]. From Figure 6a, it can be seen that the photogenerated electrons, generated from the surface of ZnO NRs, move to the MgZnO layer at first, and then move from MgZnO to ZnO NRs, which are underneath the electrode, and finally reach to the electrode. Owing to the high contact resistance among NRs, a few photogenerated electrons may pass from NRs and contribute to the photocurrent. In Figure 6b, the Schottky barrier height ΦB is calculated using forward- or reverse-biased I-V measurements and Equation (1). From Figure 6b, it can be seen that at dark, the barrier height between ZnO NRs and MgZnO (ΔEc1) is the same as that between MgZnO and ZnO NRs (ΔEc2). Under UV illumination, ΔEc2 gets larger, and ΔEc1 gets smaller at forward bias, which benefits the photogenerated electrons moving from ZnO NRs to MgZnO. Owing to existence of the small ΔEc1, the photogenerated electrons will collect together at the ZnO NRs/MgZnO interface, and then the two-dimensional electron gas (2DEG) will form [17]. The 2DEG will decrease the transverse resistances between the interface strongly [18], and then the photogenerated electrons may reach easily to Pt electrode. Therefore, compared with the PDs with ZnO seed layer, the PDs with MgZnO seed layer can realize bigger responsivity and higher detectivity.


Ultraviolet photodetectors based on ZnO nanorods-seed layer effect and metal oxide modifying layer effect.

Zhou H, Fang G, Liu N, Zhao X - Nanoscale Res Lett (2011)

Carrier transport processes in the ZnO NRs PDs. (a) Photogenerated electron transport route under UV illumination. (b) Schematic energy level diagrams of the PD with MgZnO seed layer at dark and under UV illumination, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211197&req=5

Figure 6: Carrier transport processes in the ZnO NRs PDs. (a) Photogenerated electron transport route under UV illumination. (b) Schematic energy level diagrams of the PD with MgZnO seed layer at dark and under UV illumination, respectively.
Mentions: In order to explore the enhanced performance of PDs with MgZnO seed layer, carrier transport processes in the ZnO NRs PDs under forward bias are illustrated in Figure 6a. In the dark, oxygen is adsorbed at the surface of the NRs to form a chemically adsorbed surface state. Under UV illumination, electron-hole pairs are generated when photon energy exceeds the energy band gap (hυ >Eg). Photogenerated holes move to the surface of ZnO NRs and the adsorbed oxygen is photodesorbed, and unpaired electrons in the NRs migrate to the electrodes at a bias voltage and contribute to the photocurrent [6,12]. From Figure 6a, it can be seen that the photogenerated electrons, generated from the surface of ZnO NRs, move to the MgZnO layer at first, and then move from MgZnO to ZnO NRs, which are underneath the electrode, and finally reach to the electrode. Owing to the high contact resistance among NRs, a few photogenerated electrons may pass from NRs and contribute to the photocurrent. In Figure 6b, the Schottky barrier height ΦB is calculated using forward- or reverse-biased I-V measurements and Equation (1). From Figure 6b, it can be seen that at dark, the barrier height between ZnO NRs and MgZnO (ΔEc1) is the same as that between MgZnO and ZnO NRs (ΔEc2). Under UV illumination, ΔEc2 gets larger, and ΔEc1 gets smaller at forward bias, which benefits the photogenerated electrons moving from ZnO NRs to MgZnO. Owing to existence of the small ΔEc1, the photogenerated electrons will collect together at the ZnO NRs/MgZnO interface, and then the two-dimensional electron gas (2DEG) will form [17]. The 2DEG will decrease the transverse resistances between the interface strongly [18], and then the photogenerated electrons may reach easily to Pt electrode. Therefore, compared with the PDs with ZnO seed layer, the PDs with MgZnO seed layer can realize bigger responsivity and higher detectivity.

Bottom Line: In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively.For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (Dλ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism.Also the ratio of D254* to D546* was calculated above 8 × 102 for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electronic Science and Technology and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, People's Republic of China. gjfang@whu.edu.cn.

ABSTRACT
Pt/ZnO nanorod (NR) and Pt/modified ZnO NR Schottky barrier ultraviolet (UV) photodetectors (PDs) were prepared with different seed layers and metal oxide modifying layer materials. In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively. For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (Dλ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism. Also the ratio of D254* to D546* was calculated above 8 × 102 for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.

No MeSH data available.