Skip to main content

Length-Dependent Photoelectric Property of ZnO Nanowires

Abstract

An interesting phenomenon that the photocurrent (the difference between illumination and dark current) of a ZnO nanowire (NW) under a specified voltage increased as its length increased in a certain range was observed previously and it was supposed to be mainly due to a special mean free path effect (MFPE) which caused a special distribution of dark electron density along the length with two higher electron density regions near the two ends of the NW, respectively, and the lower one in the middle part. However, such an explanation would be unreasonable and the true reasons should be the growing-process caused variation of the oxygen adsorption capacity along the NW length and the length-dependent lifetime of photogenerated carriers. Based on this understanding, a theoretical model to properly explain this phenomenon is proposed and the calculation results are in good agreement with the experimental data. This work has introduced an improved insight into the theory of the length-dependent photoelectric property of ZnO NWs.

Introduction

Photoresponse is one of the most popular methods of researching and characterizing the properties of nanomaterials [1,2,3]. In 2014, Song et al. observed that the photocurrent of a ZnO NW changed with its length at room temperature [4]. The diameter of the NW is 50 \({\text{nm}}\) and the applied voltage is 10 \({\text{V}}\). It was found that the photocurrent of the NW increased when its length increased from 40 to about 600 \({\text{nm}}\) but decreased as its length increased further. So, there was a peak in the photocurrent-length curve. This is really an interesting phenomenon. To explain this phenomenon, Song et al. assumed that the average dark electron density in a ZnO NW was inversely dependent on its length by reasoning as follows: the electrons moved without collisions in the mean free path; once electrons in valance band were excited into the conduction band at room temperature, they thought the excited electrons only in regions whose length are the mean free path near electrodes could be collected by electrodes without collision; in contrast, those in other region would move with collisions and fall into valance band; the rich electron regions, where the density of electrons was close to that excited by illumination, would be formed near two ends of the NW; the proportion of the high electron density region in the entire ZnO NW decreased with the increasing length, leading to the average electron density of the ZnO NW decreasing and finally saturating. Moreover, the valance band had no more electrons for further light excitation near two ends of the NW. The density of excited electrons contributing to the photocurrent decreased as the length reduces. Therefore, the photocurrent of a ZnO NW was more dependent on the MFPE as its length increased in the range of 40–600 \({\text{nm}}\) and relied strongly on the length as its length increased further. A peak appeared naturally in the photocurrent-length curve. In addition, they made some supplemental works, such as the research that the length-dependent photoinduced electron density from the surface of a ZnO NW which originates from the desorption of electrons confined in the NW surface [5], to improve their theory. It seems that this interesting phenomenon has been explained well.

However, their explanation has some drawbacks. Based on their reasoning, the electrons are distributed evenly in the NW under dark without bias. When the NW connects in the circuit, the excited electrons will be under collision and fall into the valance band as traveling out the mean free path. The middle part of the NW can be considered to consist of many mean free path lengths, and the excited electrons moving state and the number of electrons falling into the valance band should be the same in every mean free path. In other words, the dark electron density distributes evenly in the NW under a bias. It means that the length-dependent average electron density in a ZnO NW they assumed could not be supported by the MFPE. The MFPE should not be taken as a reason that illustrates this phenomenon. At the same time, the shift of the peak photocurrent length under different light intensities had been overlooked. A weakness of their argument is that it could not explain this ignored phenomenon well. And it is not clear the reason that the surface photoinduced electron density depends on the NW length. Consequently, it is necessary to propose a reasonable theory to explain these phenomena.

In this paper, the dependence of the OAC of a ZnO NW on the length has been studied. As its length increases, the OAC of the NW will be enhanced. It can be explained by the growing-process caused variation of oxygen vacancies (OVs) along the NW length. The results show that its depleted region width decreases and its average dark electron density increases, as the NW length decreases. In addition, LPC strongly depends on the NW length. Given the OAC and LPC, a different understanding of the photocurrent change of a ZnO NW is proposed. Based on the analysis of the effect of temperature on OAC, a qualitative analysis to explain the origin of the peak photocurrent length shifting is also given. The calculation results are consistent with the experimental data. This work provides improved insight into the photoreaction of ZnO NWs.

The Procedure of Model

Because electrical mobility is much larger than hole mobility, we ignore the contribution of holes to the photocurrent [4]. According to Ohm’s Law, we can write the photocurrent of a ZnO NW as expressions (1):

$$\Delta I = \frac{US}{L}\Delta \sigma ,\Delta \sigma = \Delta n\mu e$$
(1)

where \(U\) is the voltage, \(L\) is the length of an NW, \(S\) is the cross section of an NW, \(e\) is the electron charge, \(\mu\) is electrical mobility, and \(\Delta n\) denotes the difference of electron density between dark and illumination conditions. Ignoring the effect of OAC, \(\Delta n\) is \(n_{{{\text{pe}}}}\) which is the concentration of photogenerated electrons. Assuming reasonably that electrical mobility is constant in the NW length range we study, the change in the photocurrent of the NW can be reflected reasonably by that of \(\Delta n\) as its length varies. At the same time, the Schottky barrier height (SBH) of the NW is inversely dependent on its length, which can be observed clearly in their experiment. The SBH is closely related to the electrical transport of the NW. Generally speaking, the SBH can be modified by three factors: (1) the difference in work function between the semiconductor and contact metal, which is influenced by the level of doping concentration in the semiconductor when keeping the contact metal constant, (2) the surface state of the semiconductor, and (3) the oxide film on the semiconductor surface. However, in this paper, the SBH is only affected by the first factor because the latter two factors are unchanged for the same growing conditions. The high level of average electron density in ZnO NWs will cause low SBH [6]. As a result, the above-mentioned questions are equivalent to explaining why \(\Delta n\) and the average electron density in a ZnO NW depend on its length.

It is widely known that the process of oxygen adsorbing and desorbing on a ZnO NW surface: \({\text{O}}_{{\text{2(g)}}} + {\text{e}}^{ - } \rightleftharpoons {\text{O}}_{{\text{2(ad)}}}^{ - }\) and \({\text{O}}_{{\text{2(g)}}} + 2{\text{e}}^{ - } \rightleftharpoons 2{\text{O}}_{{\text{(ad)}}}^{ - }\) [7,8,9]. The more detailed process has already been described [10]. In a stable environment, the quantity of adsorbed oxygen molecules dominates the number of electrons captured inside the NW, significantly impacting the NW’s conductivity under dark and illumination. It is necessary to know what dominates the quantity of adsorbed oxygen molecules.

As growing ZnO NWs, varied defects usually appear in NWs, resulting in unintentional doping [11, 12]. Defects such as OVs, as we all know, usually dominate the electronic and chemical properties and adsorption behaviors [13], because OVs could provide many sites for oxygen molecules to adsorb on the surface and seize electrons [14,15,16]. We can find that the higher density of OVs can lead to more oxygen molecules adsorbing on the surface of a ZnO NW [16,17,18]. Hence, the OAC can be characterized by the density of OVs. Additionally, it is also reasonable to take the density of adsorbed oxygen to describe the OAC [15, 19] because the adsorbed oxygen molecules occupy the position of OVs in the lattice for ZnO materials [20]. During growing a ZnO NW, with its length increasing, the density of its OVs increases and finally saturates [21]. Kayaci et al. observed that the density of OVs began to increase at a ZnO thickness of approximately 40 nm [20]. In addition, the literature [4] shows that the top shape of ZnO NWs grown by Song et al. is a micro-pyramid whose OAC is weaker than that of flake and column [19]. The proportion of the micro-pyramid-shaped surface in the total surface area of the NW increases as its length decreases, which will result in the weaker OAC of the NW. Besides the effects caused by the growing process, OAC can also be affected by temperature and other external factors [22]. Sanghwa observed the oxygen re-adsorption process on a ZnO NW surface under UV illumination in the air because of the Joule heating effect [23]. It shows that a suitable high temperature will enhance the OAC of a ZnO NW. To analyze conveniently, we first do not consider the effects of Joule heating and other factors due to the low Joule power and constant environmental conditions in Ref. [4]. So, given the length-dependent OAC, it is easy to recognize that the adsorbed oxygen density \(N_{s}\) on a ZnO NW surface increases when its length increases, leading to an increase in the density of captured electrons which can be proved by the scanning results of surface potential in the report [5].

Hence, we have the length-dependent density of electrons adsorbed \(n_{c}\) on the surface of a ZnO NW as Eq. (2) [24]

$$n_{c} = \alpha N_{s}.$$
(2)

Here, \(\alpha\) is the charge transfer coefficient denoting the number of electrons captured by one chemisorbed oxygen molecule. The expression \(n_{c}\) means the number of electrostatic carriers confined on a ZnO NW surface, which can be characterized by the surface potential \(V_{sp}\). Then, we can derivate the depleted width \(r\) by the following expressions (3)–(5) [25].

$$V_{sp} = \frac{{2\pi (e\alpha N_{s} )^{2} }}{{\varepsilon N_{d} }},$$
(3)
$$\lambda_{D} = \left( {\frac{\varepsilon kT}{{2\pi e^{2} N_{d} }}} \right)^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}}},$$
(4)
$$r = \lambda_{D} \left( {\frac{{eV_{sp} }}{kT}} \right)^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}}}.$$
(5)

Here, \(\varepsilon\) is the dielectric constant, \(N_{d}\) is the concentration of donor impurity, \(k\) is the Boltzmann constant, \(T\) is the absolute temperature. To calculate the average dark electron density \(n_{{{\text{dark}}}}\) in a ZnO NW, we should know the average adsorbed electron density of a ZnO NW exposed to air in the dark which can be described by

$$n_{ac} = \frac{{2\int_{0}^{L} {\alpha N_{s} dL} }}{RL}.$$
(6)

Therefore, \(n_{{{\text{dark}}}}\) becomes

$$n_{{{\text{dark}}}} = n_{0} - n_{{{\text{ac}}}}$$
(7)

where \(n_{0}\) is the electron density of the NW before it is exposed to air, and \(R\) is the radius of the NW. When a ZnO NW length is close to 40 nm, \(N_{s}\) will become zero and \(n_{{{\text{dark}}}}\) will approximately equal a constant of \(n_{0}\). In contrast, as its length is long enough, \(N_{s}\) becomes a constant value of \(N_{s0}\) and \(n_{{{\text{dark}}}}\) will be approximately reduced to Eq. (8) [26]

$$n_{{{\text{dark}}}} = n_{0} - \frac{{2\alpha N_{s0} }}{R}.$$
(8)

As shown in Fig. 1, the distribution of electrons inside a ZnO NW exposed in the air depends strongly on its length, which is different from that in vacuum, and the depleted region width \(r\) increases with its length increases and saturates at a long length. When the light which can generate electron-hole pairs illuminates ZnO NWs, the chemisorbed oxygen will be photon-desorbed. The additional photoinduced electron density is determined by the concentration of the electrons confined inside the NW and the light intensity. As the light intensity is large enough, all electrons captured by oxygen molecules on the surface will be desorbed. Thus, \(\Delta n\) can be modified as the following expression:

$$\Delta n = n_{{{\text{pe}}}} + n_{{{\text{ac}}}}.$$
(9)
Fig. 1
figure 1

The distribution of electrons of a ZnO NW in vacuum a and in the air b

On the contrary, the number of photon-desorbed electrons is approximately equal to that of the photogenerated holes under low light intensity. The dark electron density in ZnO NWs is about \(10^{17} {\text{cm}}^{ - 3}\)[4] which is much larger than the electron density (\(10^{14} {\text{cm}}^{ - 3}\)) that light induced based on our calculation results, as shown in Fig. 2. It reveals that there are enough adsorbed electrons to be photon-desorbed for the NW in Ref. [4]. Therefore, we reasonably believe that \(\Delta n\) in Ref. [4] can be instead approximately by \(2n_{{{\text{pe}}}}\).

Fig. 2
figure 2

The difference in electron density \(\Delta n\) between illumination and dark conditions from the experimental data in Ref. [4]

Not only can the length of a ZnO NW affect OAC, but in any case, it likewise influences LPC. For ZnO NWs, the higher aspect ratio will result in fewer recombination centers with a small number of interparticle junctions and higher electron delocalization, allowing the electron-hole pairs to separate effectively and lower their recombination rate [15, 17]. The smaller the size, the higher the recombination rate of electron-hole pairs in ZnO NWs [1]. In addition, the decreasing length will cause an increase in electron concentration under dark [6], leading to a decrease in LPC [27]. It should also be noted that OVs can render defect energy levels in a ZnO NW to prevent electron-hole pairs from recombining and lead to stronger light absorption [17, 28,29,30,31]. Briefly, the high density of OVs contributes to reducing the recombination rate of electron-hole pairs and increasing the density of photoinduced electrons. More important is that Hong et al. found that the radiative recombination rate in ZnO NWs decreased as the length increased and became saturated at about 600 nm [32]. Amazingly, the length of 600 nm approaches the peak photocurrent length in Ref. [4], which points to the strong relevance between the interesting phenomenon mentioned above and the recombination rate of electron-hole pairs. It is known that LPC \(\tau\) is determined by the radiative and nonradiative lifetime: \(\frac{1}{\tau } = \frac{1}{{\tau_{r} }} + \frac{1}{{\tau_{nr} }}\) [32]. Here, \(\tau_{r}\) and \(\tau_{nr}\) are the radiative lifetime and nonradiative lifetime constants, respectively. Considering the effects of the different diameters on the \(\tau^{ - 1}\), we obtain the recombination rate per unit area \(\tau_{p}^{ - 1}\) from the experimental data of Ref. [32]. The inset in Fig. 3a reveals that the \(\tau_{p}^{ - 1}\) is more dependent on the length than the diameter from 29 to 40 nm. It can also be demonstrated in other literature [33]. We believe that \(\tau^{ - 1}\) of diameter from 29 to 50 nm in the unit area is similar at the same length. Herein, \(\tau^{ - 1}\) of a ZnO NW with a diameter of 50 nm can be calculated and described simply by

$$\uptau ^{ - 1} = 2.5 \times L^{ - 1.68} + 6.16,$$
(10)
Fig. 3
figure 3

a The length-dependent recombination rate of ZnO NWs with a diameter of 50 \({\text{nm}}\) we obtain from the model. Inset: the recombination rate \(\tau^{ - 1}\) and the recombination rate per unit area \(\tau_{p}^{ - 1}\) are calculated from the experimental data in Ref. [32]. b Comparison of the results calculated in this work with the experimental and calculation ones in Ref. [4]. Under a voltage of 10 V, the photocurrent as the function of the height of ZnO NWs with a diameter of 50 nm

as shown in Fig. 3a. Because test time is far more than \(\tau\) which is often less than 1 \(ns\) for ZnO materials [34], the density of photogenerated carriers at steady-state follows as

$$n_{{{\text{pe}}}} = \beta\upgamma \frac{I}{{{\raise0.5ex\hbox{$\scriptstyle {{\text{hc}}}$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle \lambda $}}}}\uptau.$$
(11)

Here, \(\beta\) is quantum efficiency, \(I\) is the light illumination intensity, \(h\) is Planck’s constant, \(c\) is the light speed in vacuum, and \(\upgamma\) is the material adsorption factor at the light wavelength \(\lambda\) [35], In conclusion, the photocurrent of a ZnO NW in Ref. [4] will be given by

$$\Delta I = \frac{USe\mu }{L}(2\beta \gamma \frac{I}{{{\raise0.5ex\hbox{$\scriptstyle {hc}$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle \lambda $}}}}{\uptau )}.$$
(12)

Results and Discussion

Based on the analysis of OAC and LPC, it is clear that the absorption of ZnO NWs is much more complex under the broadband light source due to OVs and other factors. Thus, to calculate conveniently, we choose \(d \times 10^{14} \times \tau\) to fit the experimental data in Ref. [4] after determining the function between \(\tau\) and the NW length. \(U\), \(R\) and \(\mu\) are the same as those in Ref. [4]. The calculation results show that \(d\) equals 7.22, and the experimental data are found to be in good agreement with our model, as shown in Fig. 3b. The photocurrent of a ZnO NW changes significantly as its length reduces. The photocurrent will decrease slowly rather than stabilize as the length increases more than 3 \({\mu m}\), which seems closer to our model. Maybe additional experimental data will make a more noticeable difference between the theory of us and Song et al. It should also be noted that their measured current is too small to make a high temperature, and electrons in the valence band are challenging to be excited into the conduction band at room temperature because of the wide band gap of ZnO materials (3.4 eV) [36]. So, the electron density they assume near two ends of the NW at room temperature could not be approximately comparable to that excited by illumination. It is not reasonable to use high temperature to explain this interesting phenomenon in Ref. [4]. At the same time, their theory can be found that the high electron density near two ends of the NW remains constant. This cannot illustrate that SBH depends on the NW length.

Furthermore, it is worth noting that the peak photocurrent length in Ref. [5] under increasing light intensities shifts to a longer length. Regrettably, this phenomenon has not been mentioned and explained. It is known that OAC plays an essential role in the photoresponse of ZnO NWs [29, 36, 37]. It can be affected strongly by temperature [23, 38]. Based on the previous reports [38, 39], OAC will be enhanced before reaching the optimal temperature for ZnO nanomaterials. In the air, under illumination, the oxygen molecules re-adsorb on the ZnO NW surface with the increasing temperature caused by Joule heating, significantly affecting the current of the ZnO NW [23]. The increasing illumination intensity makes an increase in the illumination current of the NW, resulting in the temperature caused by Joule heating increasing. In other words, the length corresponding to reaching the same temperature under the Joule heating effect for ZnO NWs becomes longer as the illumination intensity increases. It can be explained simply by \(P_{{{\text{Joule}}}} = {{U^{2} S\sigma_{{{\text{light}}}} } \mathord{\left/ {\vphantom {{U^{2} S\sigma_{{{\text{light}}}} } L}} \right. \kern-\nulldelimiterspace} L}\), where \(P_{{{\text{Joule}}}}\) is the Joule power and \(\sigma_{{{\text{light}}}}\) is the conductivity of ZnO nanomaterials under illumination. To keep \(P_{{{\text{Joule}}}}\) constant, the length will be longer when \(\sigma_{{{\text{light}}}}\) increases. According to the analysis above, it is clear that the re-adsorption process will significantly accelerate the decrease of \(\Delta n\) under the significant Joule heating. Besides, the high temperature makes more electrons excited from the valence band to the conduction band in ZnO NWs under dark conditions to increase the dark current. As a result, the peak photocurrent length of a ZnO NW will shift to a longer length with the increasing illumination light intensity. Combined with the temperature, our model can explain the peak photocurrent length shifting qualitatively under different illumination intensities. However, the theory of Song et al. could not illustrate this interesting phenomenon. According to our theory, the reason why the photoinduced electron density originated from the NW surface and \(\Delta n\) change with its length becomes clear. Given the present experimental conditions, it should be mentioned that we have just provided a calculating method and have not given a definite distribution of \(N_{s}\) along the growth length of a ZnO NW. A further study with more focus on \(N_{s}\) is therefore suggested. Our work provides new insight into the photoresponse of ZnO nanomaterials and may be helpful to optimize devices.

Conclusions

A length-dependent model to interpret reasonably the photocurrent change of ZnO NWs is proposed based on the OAC and LPC. This study has shown that the length-dependent OAC is due to the shape of ZnO NWs and the growing-process caused variation of OVs along the NW length. Our theory shows that the dark electron density and the width of the depleted region vary when its length changes. Combined with the effect of temperature on OAC, the peak photocurrent length shifting can be explained qualitatively. The calculation results are in good agreement with the experimental data. Our work provides a new understanding of the photoresponse of ZnO NWs.

Availability of data and material

The data supporting the findings of this study are available from the corresponding author on reasonable request.

Abbreviations

NW:

Nanowire

MFPE:

Mean free path effect

OAC:

Oxygen adsorption capacity

LPC:

Lifetime of photogenerated carriers

OVs:

Oxygen vacancies

SBH:

Schottky barrier height

References

  1. Baxter JB, Schmuttenmaer CA (2006) Conductivity of ZnO nanowires, nanoparticles, and thin films using time-resolved terahertz spectroscopy. J Phys Chem B 110:25229. https://doi.org/10.1021/jp064399a

    CAS  Article  Google Scholar 

  2. Fry PW, Itskevich IE, Parnell SR et al (2000) Photocurrent spectroscopy of InAs/GaAs self-assembled quantum dots. Phys Rev B 62:16784. https://doi.org/10.1103/PhysRevB.62.16784

    CAS  Article  Google Scholar 

  3. Men X, Chen H, Chang K et al (2016) Three-dimensional free-standing ZnO/graphene composite foam for photocurrent generation and photocatalytic activity. Appl Catal B 187:367. https://doi.org/10.1016/j.apcatb.2016.01.052

    CAS  Article  Google Scholar 

  4. Jiang C, Song J (2014) Significant photoelectric property change caused by additional nano-confinement: a study of half-dimensional nanomaterials. Small 10:5042. https://doi.org/10.1002/smll.201400704

    CAS  Article  Google Scholar 

  5. Tang C, Jiang C, Bi S et al (2016) Photoelectric property modulation by nanoconfinement in the longitude direction of short semiconducting nanorods. ACS Appl Mater Interfaces 8:11001. https://doi.org/10.1021/acsami.6b02497

    CAS  Article  Google Scholar 

  6. Rivera VF, Auras F, Motto P et al (2013) Length-dependent charge generation from vertical arrays of high-aspect-ratio ZnO nanowires. Chem Eur J 19:14665. https://doi.org/10.1002/chem.201204429

    CAS  Article  Google Scholar 

  7. Ghimbeu CM, Schoonman J, Lumbreras M et al (2007) Electrostatic spray deposited zinc oxide films for gas sensor applications. Appl Surf Sci 253:7483. https://doi.org/10.1016/j.apsusc.2007.03.039

    CAS  Article  Google Scholar 

  8. Hsueh T-J, Hsu C-L, Chang S-J et al (2007) Laterally grown ZnO nanowire ethanol gas sensors. Sens Actuators B Chem 126:473. https://doi.org/10.1016/j.snb.2007.03.034

    CAS  Article  Google Scholar 

  9. Zou G, Xu Y, Wang S et al (2015) The synergistic effect in Co–Ce oxides for catalytic oxidation of diesel soot. Catal Sci Technol 5:1084. https://doi.org/10.1039/c4cy01141d

    CAS  Article  Google Scholar 

  10. Zhou J, Gu Y, Hu Y et al (2009) Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization. Appl Phys Lett 94:191103. https://doi.org/10.1063/1.3133358

    CAS  Article  Google Scholar 

  11. Fan JC, Sreekanth KM, Xie Z et al (2013) p-Type ZnO materials: theory, growth, properties and devices. Prog Mater Sci 58:874. https://doi.org/10.1016/j.pmatsci.2013.03.002

    CAS  Article  Google Scholar 

  12. Khan MA, Wahab Y, Muhammad R et al (2018) Catalyst-free fabrication of novel ZnO/CuO core-Shell nanowires heterojunction: controlled growth, structural and optoelectronic properties. Appl Surf Sci 435:718. https://doi.org/10.1016/j.apsusc.2017.11.071

    CAS  Article  Google Scholar 

  13. Yan Y, Al-Jassim MM, Wei S-H (2005) Oxygen-vacancy mediated adsorption and reactions of molecular oxygen on theZnO(101¯0)surface. Phys Rev B. https://doi.org/10.1103/PhysRevB.72.161307

    Article  Google Scholar 

  14. Chen Y, Wang X, Shi C et al (2015) Sensing mechanism of SnO2(1 1 0) surface to H2: density functional theory calculations. Sens Actuators B Chem 220:279. https://doi.org/10.1016/j.snb.2015.05.061

    CAS  Article  Google Scholar 

  15. Leelavathi A, Madras G, Ravishankar N (2013) Origin of enhanced photocatalytic activity and photoconduction in high aspect ratio ZnO nanorods. Phys Chem Chem Phys 15:10795. https://doi.org/10.1039/c3cp51058a

    CAS  Article  Google Scholar 

  16. Tang W (2017) Sensing mechanism of SnO2/ZnO nanofibers for CH3OH sensors: heterojunction effects. J Phys D Appl Phys. https://doi.org/10.1088/1361-6463/aa90b5

    Article  Google Scholar 

  17. Zhang X, Qin J, Xue Y et al (2014) Effect of aspect ratio and surface defects on the photocatalytic activity of ZnO nanorods. Sci Rep 4:4596. https://doi.org/10.1038/srep04596

    CAS  Article  Google Scholar 

  18. Zhang Y, Liu Y, Zhou L et al (2018) The role of Ce doping in enhancing sensing performance of ZnO-based gas sensor by adjusting the proportion of oxygen species. Sens Actuators B Chem 273:991. https://doi.org/10.1016/j.snb.2018.05.167

    CAS  Article  Google Scholar 

  19. Han X-G, He H-Z, Kuang Q et al (2009) Controlling morphologies and tuning the related properties of nano/microstructured ZnO crystallites. J Phys Chem C 113:584. https://doi.org/10.1021/jp808233e

    CAS  Article  Google Scholar 

  20. Kayaci F, Vempati S, Donmez I et al (2014) Role of zinc interstitials and oxygen vacancies of ZnO in photocatalysis: a bottom-up approach to control defect density. Nanoscale 6:10224. https://doi.org/10.1039/c4nr01887g

    CAS  Article  Google Scholar 

  21. Ridha NJ, Alosfur FKM, Jumali MHH et al (2018) Dimensional effect of ZnO nanorods on gas-sensing performance. J Phys D Appl Phys. https://doi.org/10.1088/1361-6463/aadecb

    Article  Google Scholar 

  22. Li QH, Wan Q, Liang YX et al (2004) Electronic transport through individual ZnO nanowires. Appl Phys Lett 84:4556. https://doi.org/10.1063/1.1759071

    CAS  Article  Google Scholar 

  23. Yoon S, Lim J-H, Yoo B (2012) Oxygen re-adsorption of a single ZnO nanobridge by joule heating under ultraviolet illumination. Appl Phys Express. https://doi.org/10.1143/apex.5.105003

    Article  Google Scholar 

  24. Fan Z, Lu JG (2005) Gate-refreshable nanowire chemical sensors. Appl Phys Lett. https://doi.org/10.1063/1.1883715

    Article  Google Scholar 

  25. Lupan O, Chow L, Pauporté T et al (2012) Highly sensitive and selective hydrogen single-nanowire nanosensor. Sens Actuators B Chem 173:772. https://doi.org/10.1016/j.snb.2012.07.111

    CAS  Article  Google Scholar 

  26. Zhiyong F, Lu JG (2006) Chemical sensing with ZnO nanowire field-effect transistor. IEEE Trans Nanotechnol 5:393. https://doi.org/10.1109/tnano.2006.877428

    Article  Google Scholar 

  27. Yang Y, Li J, Wu H et al (2012) Controlled ambipolar doping and gate voltage dependent carrier diffusion length in lead sulfide nanowires. Nano Lett 12:5890. https://doi.org/10.1021/nl303294k

    CAS  Article  Google Scholar 

  28. Flemban TH, Singaravelu V, Sasikala Devi AA et al (2015) Homogeneous vertical ZnO nanorod arrays with high conductivity on an in situ Gd nanolayer. RSC Adv 5:94670. https://doi.org/10.1039/c5ra19798h

    CAS  Article  Google Scholar 

  29. Kushwaha A, Aslam M (2012) Defect induced high photocurrent in solution grown vertically aligned ZnO nanowire array films. J Appl Phys. https://doi.org/10.1063/1.4749808

    Article  Google Scholar 

  30. Wang J, Liu P, Fu X et al (2009) Relationship between oxygen defects and the photocatalytic property of ZnO nanocrystals in nafion membranes. Langmuir 25:1218. https://doi.org/10.1021/la803370z

    CAS  Article  Google Scholar 

  31. Wang J, Wang Z, Huang B et al (2012) Oxygen vacancy induced band-gap narrowing and enhanced visible light photocatalytic activity of ZnO. ACS Appl Mater Interfaces 4:4024. https://doi.org/10.1021/am300835p

    CAS  Article  Google Scholar 

  32. Hong S, Joo T, Park WI et al (2003) Time-resolved photoluminescence of the size-controlled ZnO nanorods. Appl Phys Lett 83:4157. https://doi.org/10.1063/1.1627472

    CAS  Article  Google Scholar 

  33. Reparaz JS, Güell F, Wagner MR et al (2010) Size-dependent recombination dynamics in ZnO nanowires. Appl Phys Lett. https://doi.org/10.1063/1.3294327

    Article  Google Scholar 

  34. Bao J, Shalish I, Su Z et al (2011) Photoinduced oxygen release and persistent photoconductivity in ZnO nanowires. Nanoscale Res Lett 6:404. https://doi.org/10.1186/1556-276X-6-404

    CAS  Article  Google Scholar 

  35. Liu E, Zhu B, Luo J (2017) The physics of semiconductors, 7th edn. Publishing House of Electronics Industry, Beijing

    Google Scholar 

  36. Fan S-W, Srivastava AK, Dravid VP (2009) UV-activated room-temperature gas sensing mechanism of polycrystalline ZnO. Appl Phys Lett. https://doi.org/10.1063/1.3243458

    Article  Google Scholar 

  37. Li QH, Gao T, Wang YG et al (2005) Adsorption and desorption of oxygen probed from ZnO nanowire films by photocurrent measurements. Appl Phys Lett. https://doi.org/10.1063/1.1883711

    Article  Google Scholar 

  38. Ke J-J, Liu Z-J, Kang C-F et al (2011) Surface effect on resistive switching behaviors of ZnO. Appl Phys Lett. https://doi.org/10.1063/1.3659296

    Article  Google Scholar 

  39. Prades JD, Jimenez-Diaz R, Hernandez-Ramirez F et al (2008) Ultralow power consumption gas sensors based on self-heated individual nanowires. Appl Phys Lett. https://doi.org/10.1063/1.2988265

    Article  Google Scholar 

Download references

Acknowledgements

Not applicable.

Funding

This work was supported by National Natural Science Foundation of China (No. 61674020), National Key Research and Development Program of China (No. 2018YFB2200104), Beijing Municipal Science & Technology Commission (No. Z191100004819012), 111 Project of China (No. BP0719012), Science Fund for Creative Research Groups (Fund for Creative Research Groups) (No. 62021005), Fund of State Key Laboratory of IPOC at BUPT and Beijing Municipal International Science and Technology Cooperation Base of Information Optoelectronics and Nanoheterostructures.

Author information

Authors and Affiliations

Authors

Contributions

RR proposed the theoretical model, calculated the data, analyzed the results and drafted the paper. XR supervised the theoretical model and helped correction of the manuscript. HL helped analyze the results. YH and WY contributed to finishing the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Xiaomin Ren.

Ethics declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

All authors agree to the publication of the paper in the Nanoscale Research Letters.

Competing interests

The authors declare no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Ren, R., Ren, X., Liu, H. et al. Length-Dependent Photoelectric Property of ZnO Nanowires. Nanoscale Res Lett 17, 76 (2022). https://doi.org/10.1186/s11671-022-03715-2

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s11671-022-03715-2

Keywords

  • Nanowires
  • Length-dependent
  • Oxygen vacancies
  • Oxygen adsorption capacity
  • Lifetime