**4. ZnO/SiO2/Si UV photodiodes in a strong magnetic field**

**Figure 9.** shows the cross-section of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure completed configuration in a strong magnetic field [50].

In recent years, diluted magnetic semiconductors (DMSs) are attracted much great scientific interest because of their unique spintronics properties with potential technological applica‐ tions. Consequently, the high Curie temperature ferromagnetism of ZnO and related materi‐ als, doped with transition metal (TM) ions, is also expected to have applications in spintronics, including in information storage and data-processing devices [56]. The electron‐ ic, optical and magnetic properties of TM-doped ZnO and related materials have been stud‐ ied extensively [57-64]. However, the behavior and characteristics of ZnO optoelectronic devices in a magnetic field have seldom been investigated. Photodiodes with a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure in a magnetic field (Faraday configuration) as shown in Figure 9 were studied [50,51].

Figure 10 (a) plots the *I-V* characteristics of photodiodes that were measured in the dark (dark current), under illumination with a xenon arc lamp at 100 W, and in magnetic fields of 0, 0.1, 0.5 and 0.7 T, at applied reverse biases ranging from 0 to 1 V at room temperature. The mag‐ netic field-induced photocurrents were 3.02×10-5, 4.89×10-5, 1.02×10-4, and 2.27×10-4 A in mag‐ netic fields of 0, 0.1, 0.5 and 0.7 T, respectively, at a reverse bias of 1 V. However, the dark current in various magnetic fields remains almost constant (~1.27×10-8 A). Evidently, the pho‐ tocurrent/dark-current contrast ratios are about four orders of magnitude in magnetic field. A change of the applied magnetic field does not noticeably change the total current in the dark. However, when the photodiode was illuminated, the total current significantly increases by approximately one order of magnitude under a strong magnetic field, such as 0.7 T.

The total current can be described as

$$I\_{Total} = I\_{Dark} + I\_{Light} + I\_{Magnesium} \tag{4}$$

exponentially increases with the applied magnetic field because the probability of photo-ex‐ citation increased [65,66]. This phenomenon is called the magneto-optical multiplication effect. The magneto-optical current multiplication effect may be caused by photo-ionization

Si-Based ZnO Ultraviolet Photodiodes http://dx.doi.org/10.5772/48825 205

Figure 11(a) and 11(b) show the *I-V* characteristics of photodiodes measured under illumi‐ nation with a xenon arc lamp at various operating power levels, and in a magnetic field of 0.5 T at applied reverse biases from 0 to 1 V at room temperature. Figure 11(b) depicts the magneto-induced current calculated in Eq. (4), showing that the magneto-induced current increases exponentially as the reverse bias increases. Figure 11(c) plots the photocurrent as a function of wavelength in the ranges 300-720 nm for a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode, measured throughout this work at a reverse bias of 1 V. The cur‐ rent variation of the photodiode was obvious when the wavelength of incident light was lower, around 375 nm (higher photon energy). Therefore, the photo-ionization due to quan‐ tized magnetic effect of nanostructure ZnO film is apparently the source the magneto-in‐

**Figure 11.** a) and (b) Illuminated and magnetic field applied *I-V* characteristics of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode with a xenon arc lamp at various operating power and magnetic field of 0.5 T

Figure 12(a) plots the responsivity as a function of wavelength for a photodiode with the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure, measured throughout this work at a reverse bias of 1 V at which the system is in a stable optoelectronic regime. Peak A located at around 410 nm is interpreted as the excitonic absorption in the ZnO film. Peak B (around 470 nm)

applied. (c) Photocurrent as a function of wavelength in the ranges 300-720 nm [51].

due to the quantized magnetic effect of ZnO film in the photodiode structure.

duced current [65,66].

where *I Dark* is the dark current, *I Light* is the photocurrent or photo-generated current, and *I Magnetism* is the magnetic field-induced current or magneto-induced current.

**Figure 10.** a) The *I-V* characteristics of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode in the dark, illu‐ minated and under an applied magnetic field. (b) Total current at a reverse bias of 1 V against various magnetic fields [50].

Figure 10(b) a plots the total current at a reverse bias of 1 V as a function of the magnetic field. In the case of non-illumination, applying a magnetic field only slightly changed the to‐ tal current because of the absence of photo-ionization. However, under illumination, *I Magnetism* exponentially increases with the applied magnetic field because the probability of photo-ex‐ citation increased [65,66]. This phenomenon is called the magneto-optical multiplication effect. The magneto-optical current multiplication effect may be caused by photo-ionization due to the quantized magnetic effect of ZnO film in the photodiode structure.

als, doped with transition metal (TM) ions, is also expected to have applications in spintronics, including in information storage and data-processing devices [56]. The electron‐ ic, optical and magnetic properties of TM-doped ZnO and related materials have been stud‐ ied extensively [57-64]. However, the behavior and characteristics of ZnO optoelectronic devices in a magnetic field have seldom been investigated. Photodiodes with a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure in a magnetic field (Faraday configuration) as shown in

Figure 10 (a) plots the *I-V* characteristics of photodiodes that were measured in the dark (dark current), under illumination with a xenon arc lamp at 100 W, and in magnetic fields of 0, 0.1, 0.5 and 0.7 T, at applied reverse biases ranging from 0 to 1 V at room temperature. The mag‐ netic field-induced photocurrents were 3.02×10-5, 4.89×10-5, 1.02×10-4, and 2.27×10-4 A in mag‐ netic fields of 0, 0.1, 0.5 and 0.7 T, respectively, at a reverse bias of 1 V. However, the dark current in various magnetic fields remains almost constant (~1.27×10-8 A). Evidently, the pho‐ tocurrent/dark-current contrast ratios are about four orders of magnitude in magnetic field. A change of the applied magnetic field does not noticeably change the total current in the dark. However, when the photodiode was illuminated, the total current significantly increases by

approximately one order of magnitude under a strong magnetic field, such as 0.7 T.

*Magnetism* is the magnetic field-induced current or magneto-induced current.

where *I Dark* is the dark current, *I Light* is the photocurrent or photo-generated current, and *I*

**Figure 10.** a) The *I-V* characteristics of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode in the dark, illu‐ minated and under an applied magnetic field. (b) Total current at a reverse bias of 1 V against various magnetic fields

Figure 10(b) a plots the total current at a reverse bias of 1 V as a function of the magnetic field. In the case of non-illumination, applying a magnetic field only slightly changed the to‐ tal current because of the absence of photo-ionization. However, under illumination, *I Magnetism*

*ITotal* = *IDark* + *I Light* + *IMagnetism* (4)

Figure 9 were studied [50,51].

204 Photodiodes - From Fundamentals to Applications

The total current can be described as

[50].

Figure 11(a) and 11(b) show the *I-V* characteristics of photodiodes measured under illumi‐ nation with a xenon arc lamp at various operating power levels, and in a magnetic field of 0.5 T at applied reverse biases from 0 to 1 V at room temperature. Figure 11(b) depicts the magneto-induced current calculated in Eq. (4), showing that the magneto-induced current increases exponentially as the reverse bias increases. Figure 11(c) plots the photocurrent as a function of wavelength in the ranges 300-720 nm for a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode, measured throughout this work at a reverse bias of 1 V. The cur‐ rent variation of the photodiode was obvious when the wavelength of incident light was lower, around 375 nm (higher photon energy). Therefore, the photo-ionization due to quan‐ tized magnetic effect of nanostructure ZnO film is apparently the source the magneto-in‐ duced current [65,66].

**Figure 11.** a) and (b) Illuminated and magnetic field applied *I-V* characteristics of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode with a xenon arc lamp at various operating power and magnetic field of 0.5 T applied. (c) Photocurrent as a function of wavelength in the ranges 300-720 nm [51].

Figure 12(a) plots the responsivity as a function of wavelength for a photodiode with the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure, measured throughout this work at a reverse bias of 1 V at which the system is in a stable optoelectronic regime. Peak A located at around 410 nm is interpreted as the excitonic absorption in the ZnO film. Peak B (around 470 nm) may be attributed to the band-to-deep level absorption in the ZnO film. Peak B (around 470 nm) may be attributed to the band-to-deep level absorption in the ZnO film. The band ab‐ sorption edge of responsivity in the absence of a magnetic field is located at a wavelength of around 371 nm, which corresponds to the band-to-band absorption of the ZnO film [54]. In this work, the responsivity (*R*) and quantum efficiency (*QE*) at 410 nm under an applied magnetic field of 0.5 T are 0.25 A/W and ~76 %, respectively. *R* and *QE* at 410 nm in the ab‐ sence of an applied magnetic field are 0.20 A/W and ~61 %, respectively. Therefore, Eq. (1) had to modify, *R* is given by [27]

$$R = I\_{ph} \;/\; P\_{inc} = \eta \zeta \frac{q}{\hbar \nu} (A / W) \tag{5}$$

of 0.1, 0.5, and 0.7 Tesla shifted to 370, 369, and 368.5 nm, respectively, while the photon en‐ ergy shifts were approximately 4.51, 9.03, and 18.11 meV, respectively. This result suggests

Hence, according to the discussion above, a carrier transport model can be used to descript the magneto-induced current. Figure 13(b) shows that the dark current and photocurrent

where *J <sup>S</sup>* is the surface recombination current through the surface states, *J Tp* is the hole tun‐ neling current, *J Tn* is the electron current through surface states, *J <sup>T</sup>* is the tunneling current, *J <sup>D</sup>* is the current in the depletion region, and *J <sup>L</sup>* is the photo-generated current. The subscripts *n* and *p* indicate electron and hole, respectively. The magneto-induced current is given by

where the subscript *m* indicates magnetism. Therefore, in the case of non-illumination or low flux irradiations, applying a magnetic field barely changed the total current. This is be‐ cause the surface recombination velocity is so fast such that the carriers cannot produce pho‐ to-ionization. However, in the case of high flux irradiations, the probability of the photoionization increases as the photo-generated excess carrier increases. This phenomenon is called as magneto-optical multiplication effect, and is caused by the photo-ionization due to

**Figure 13.** a) Photocurrent as a function of wavelength in the ranges 350-410 nm for a *p*-ZnO/SiO2 ultrathin interlay‐ er/*n*-Si structure photodiode (b) Schematic energy-band diagram of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si system in

+ *IDp*

*IMagnetism* = *ITm* + *IDm* + *I Lm* (8)

+ *ITn* (6)

+ *I Lp* (7)

Si-Based ZnO Ultraviolet Photodiodes http://dx.doi.org/10.5772/48825 207

that the magnetic field splits the conduction-band edge into Landau levels.

*IDark* = *IS* + *ITp*

*I Light* = *ITn* + *IDn* + *I Ln* + *ITp*

can be respectively described as [30,49,53]

quantized magnetic effect of nanostructure ZnO film.

the presence of a magnetic field under illumination [51].

and

where the gain factor, *ζ*, is governed by the magneto-optic multiplication effect. In an ap‐ plied magnetic field of 0.5 T, the band absorption edge of responsivity shifts to 370 nm. The photon energy has shifted by approximately 9.03 meV. This result suggests that the magnet‐ ic field splits the conduction-band edge into Landau levels with a spacing of <sup>1</sup> <sup>2</sup> <sup>ℏ</sup>*ωce*, and the valence-band edge into Landau levels with a spacing of <sup>1</sup> <sup>2</sup> <sup>ℏ</sup>*ωch* , as displayed in Figure 12 (b), where ℏ is the reduced Planck's constant, *ωce* is the cyclotron resonance frequency of electrons, and *ωch* is the cyclotron resonance frequency of holes. Accordingly, this process is referred as the interband magneto-optic absorption due to the Landau splitting.

**Figure 12.** a) Responsivity as a function of wavelength for the photodiode with *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure at a reverse bias of 1 V. (b) Schematic band diagram to elucidate the responsivity [50].

Figure 13(a) plots the photocurrent as a function of wavelength in the range of 350-410 nm for a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode, measured throughout this work at a reverse bias of 1 V. All spectra were normalized to clarify the photon energy shift. The absorption edge of photodiode without an applied magnetic field was at a wavelength of approximately 370.5 nm. The absorption edge of photodiode with applied magnetic field of 0.1, 0.5, and 0.7 Tesla shifted to 370, 369, and 368.5 nm, respectively, while the photon en‐ ergy shifts were approximately 4.51, 9.03, and 18.11 meV, respectively. This result suggests that the magnetic field splits the conduction-band edge into Landau levels.

Hence, according to the discussion above, a carrier transport model can be used to descript the magneto-induced current. Figure 13(b) shows that the dark current and photocurrent can be respectively described as [30,49,53]

$$I\_{Dark} = I\_S + I\_{Tp} + I\_{Tn} \tag{6}$$

and

may be attributed to the band-to-deep level absorption in the ZnO film. Peak B (around 470 nm) may be attributed to the band-to-deep level absorption in the ZnO film. The band ab‐ sorption edge of responsivity in the absence of a magnetic field is located at a wavelength of around 371 nm, which corresponds to the band-to-band absorption of the ZnO film [54]. In this work, the responsivity (*R*) and quantum efficiency (*QE*) at 410 nm under an applied magnetic field of 0.5 T are 0.25 A/W and ~76 %, respectively. *R* and *QE* at 410 nm in the ab‐ sence of an applied magnetic field are 0.20 A/W and ~61 %, respectively. Therefore, Eq. (1)

where the gain factor, *ζ*, is governed by the magneto-optic multiplication effect. In an ap‐ plied magnetic field of 0.5 T, the band absorption edge of responsivity shifts to 370 nm. The photon energy has shifted by approximately 9.03 meV. This result suggests that the magnet‐

(b), where ℏ is the reduced Planck's constant, *ωce* is the cyclotron resonance frequency of electrons, and *ωch* is the cyclotron resonance frequency of holes. Accordingly, this process is

**Figure 12.** a) Responsivity as a function of wavelength for the photodiode with *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si

Figure 13(a) plots the photocurrent as a function of wavelength in the range of 350-410 nm for a *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structure photodiode, measured throughout this work at a reverse bias of 1 V. All spectra were normalized to clarify the photon energy shift. The absorption edge of photodiode without an applied magnetic field was at a wavelength of approximately 370.5 nm. The absorption edge of photodiode with applied magnetic field

structure at a reverse bias of 1 V. (b) Schematic band diagram to elucidate the responsivity [50].

*<sup>h</sup><sup>ν</sup>* (*<sup>A</sup>* / *<sup>W</sup>* ) (5)

<sup>2</sup> <sup>ℏ</sup>*ωce*, and the

<sup>2</sup> <sup>ℏ</sup>*ωch* , as displayed in Figure 12

*<sup>R</sup>* <sup>=</sup> *<sup>I</sup> ph* / *Pinc* <sup>=</sup>*ηζ <sup>q</sup>*

ic field splits the conduction-band edge into Landau levels with a spacing of <sup>1</sup>

referred as the interband magneto-optic absorption due to the Landau splitting.

valence-band edge into Landau levels with a spacing of <sup>1</sup>

had to modify, *R* is given by [27]

206 Photodiodes - From Fundamentals to Applications

$$I\_{Llight} = I\_{Tn} + I\_{Dn} + I\_{Ln} + I\_{Tp} + I\_{Dp} + I\_{Lp} \tag{7}$$

where *J <sup>S</sup>* is the surface recombination current through the surface states, *J Tp* is the hole tun‐ neling current, *J Tn* is the electron current through surface states, *J <sup>T</sup>* is the tunneling current, *J <sup>D</sup>* is the current in the depletion region, and *J <sup>L</sup>* is the photo-generated current. The subscripts *n* and *p* indicate electron and hole, respectively. The magneto-induced current is given by

$$I\_{Magnetic} = I\_{Tm} + I\_{Dm} + I\_{Lm} \tag{8}$$

where the subscript *m* indicates magnetism. Therefore, in the case of non-illumination or low flux irradiations, applying a magnetic field barely changed the total current. This is be‐ cause the surface recombination velocity is so fast such that the carriers cannot produce pho‐ to-ionization. However, in the case of high flux irradiations, the probability of the photoionization increases as the photo-generated excess carrier increases. This phenomenon is called as magneto-optical multiplication effect, and is caused by the photo-ionization due to quantized magnetic effect of nanostructure ZnO film.

**Figure 13.** a) Photocurrent as a function of wavelength in the ranges 350-410 nm for a *p*-ZnO/SiO2 ultrathin interlay‐ er/*n*-Si structure photodiode (b) Schematic energy-band diagram of the *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si system in the presence of a magnetic field under illumination [51].

#### **5. Conclusions**

In summary, both *p*-ZnO/*n*-Si and *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structures UV photo‐ diodes have been introduced. In the aspect of *p*-ZnO/*n*-Si photodiodes, the photoresponses exhibited higher responsive regions at UV, visible and near infrared ranges. In the aspect of *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si photodiodes, placing in a strong magnetic field, the magneto-induced current in photodiode increases exponentially as the reverse bias and illu‐ mination flux increases, mainly because the magnetic field induced a photocurrent by mag‐ neto-optical multiplication effects. In the various magnetic fields, the absorption tails of the responsivity were shifted from 370.5 nm to 368.5 nm, and a blue shift of the photon energy from 4.52 meV to 18.16 meV were observed. This shift is attributed to the interband magne‐ to-optical absorption caused by Landau splitting. Therefore, the magneto-optical current multiplication effect may be caused by the photo-ionization owing to quantized magnetic ef‐ fect of the ZnO film. We hope all these contents may be helpful for the readers and compre‐ hend the development of ZnO/SiO2/Si UV photodiodes.

[7] Barnes, T. M., Leaf, J., Hand, S., Fry, C., & Wolden, C. A. (2004). A comparison of plasma-activated N2/O2 and N2O/O2 mixtures for use in ZnO:N synthesis by chemical

Si-Based ZnO Ultraviolet Photodiodes http://dx.doi.org/10.5772/48825 209

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#### **Author details**

#### Lung-Chien Chen\*

Department of Electro-optical Engineering, National Taipei University of Technology, 1, sec. 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan, Republic of China

#### **References**


[7] Barnes, T. M., Leaf, J., Hand, S., Fry, C., & Wolden, C. A. (2004). A comparison of plasma-activated N2/O2 and N2O/O2 mixtures for use in ZnO:N synthesis by chemical vapor deposition. J. Appl. Phys. 2004 , 96(12), 7036-44.

**5. Conclusions**

208 Photodiodes - From Fundamentals to Applications

**Author details**

Lung-Chien Chen\*

**References**

2002 , 81(17), 3272-4.

In summary, both *p*-ZnO/*n*-Si and *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si structures UV photo‐ diodes have been introduced. In the aspect of *p*-ZnO/*n*-Si photodiodes, the photoresponses exhibited higher responsive regions at UV, visible and near infrared ranges. In the aspect of *p*-ZnO/SiO2 ultrathin interlayer/*n*-Si photodiodes, placing in a strong magnetic field, the magneto-induced current in photodiode increases exponentially as the reverse bias and illu‐ mination flux increases, mainly because the magnetic field induced a photocurrent by mag‐ neto-optical multiplication effects. In the various magnetic fields, the absorption tails of the responsivity were shifted from 370.5 nm to 368.5 nm, and a blue shift of the photon energy from 4.52 meV to 18.16 meV were observed. This shift is attributed to the interband magne‐ to-optical absorption caused by Landau splitting. Therefore, the magneto-optical current multiplication effect may be caused by the photo-ionization owing to quantized magnetic ef‐ fect of the ZnO film. We hope all these contents may be helpful for the readers and compre‐

Department of Electro-optical Engineering, National Taipei University of Technology, 1, sec.

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**Chapter 7**

**Infrared Photodiodes on**

Andriy Tkachuk

**1. Introduction**

ues predicted theoretically.

InAs/GaInSb type-II superlattice photodiodes.

http://dx.doi.org/10.5772/52930

Volodymyr Tetyorkin, Andriy Sukach and

Additional information is available at the end of the chapter

**II-VI and III-V Narrow-Gap Semiconductors**

During the last two decades HgCdTe, InSb and InAs infrared (IR) photodiodes have de‐ veloped rapidly for utilization in second generation thermal-imaging systems. Obviously, they are regarded as the most important candidates for development of third generation systems as well. Despite this fact many problems still exist in manufacturing technology as well as in understanding of physical phenomena in materials and photodiodes. As a re‐ sult, threshold parameters of commercially available IR photodiodes are far from the val‐

The concept of band gap engineering have found numerous applications in the fabrication IR devices on II-VI and V III-V semiconductors. For instance, the most important advantage of HgCdTe ternary alloy is ability to tune its energy band gap in wide range. The spectral cutoff of HgCdTe photodiodes can be tailored by adjusting the HgCdTe alloy composition over the 1-30 mm range. Further application of this concept in technology of IR detectors is closely connected with development of GaAs/AlGaAs multiple quantum well detectors and

To implement the concept of defect engineering, grown-in and process-induced defects must be minimized and passivated or eliminated. Defects in narrow-gap semiconductors are easily introduced either intentionally or unintentionally during crystal growth, sample treat‐ ment and device processing. There are also evidences that these defects are electrically ac‐ tive. So, for controlling parameters and characteristics of infrared photodiodes on narrowgap semiconductors through defect engineering, it is essential to understand physical properties of defects, mechanisms of their interaction and temporal evolution. Electronic

> © 2012 Tetyorkin et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Tetyorkin et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
