**8. Measurement of InP photodiode's reflectance**

To realize our experiments related to measuring the reflectance of InGaAs/InP photodiodes the experimental set-up presented in figure 4 hasbeen arranged.

An incandescence lamp is the white light source imaged at the input slit of the monochro‐ mator. This lamp was able to cover the spectral range from 800 nm to 1600 nm and appro‐ priate blocking filters for second – order wavelengths were added to the monochromator. After the monochromator, a linear polarizer and a beam splitter, which serves to monitor temporal power fluctuations,were placed. A germanium photodiode was used as the moni‐ toring reference photodetector. More details can be seen in reference [20].

The experimental set-up included an optical system of mirrors, which consists of two parts. An upper part (see mirror 7 and germanium photodiode 9) realized monitoring temporal fluctuations of light power. A bottom part (see mirrors 8, 11; InGaAs/InP-photodiode 10, and and germanium photodiode 12) formed an image of the monochromator's exit slit on the sensitive surfaces of photodiodes. The angle of incidence was equal to 7.4 º which was accepted as the normal incidence in this train of measurements.

**Figure 4.** Experimental set-up for measuring the reflectance InGaAs/InP photodiodes

The measurement method consists in comparing the response from a germanium photo‐ diode to the radiation reflected by the InGaAs/InP photodiode with the response from an aluminum standard mirror whose reflectance is measured as in [21], so that [20]:

$$\rho(\mathcal{X}) = \frac{I\_p(\mathcal{X})}{I\_m(\mathcal{X})} \rho\_m(\mathcal{X}) \tag{6}$$

Here,*I <sup>p</sup> (λ)* is the response to the light reflected by

The group known as III-V hetero-structures has yield different photodiodes in the near IR range, particularly those based on InP/InGaAs has yield very good devices for the spectral range covered by germanium photodiodes. This hetero-structure has got two junctions in fact. The InGaAs material, having a lower gap, is kept in between two layers on InPwhose gap is bigger and hence transparent to the wavelength region used in optical communica‐ tions: the nondispersion wavelength (1.3μm) and the loss minimum wavelength (1.55μm). The radiometric characteristics of these InP-based photodetectors are superior to those of conventional photodiodes composed of elemental Germanium. Because of that they have re‐

By using a hetero-structure, which hadn't been used in group IV elemental semiconductors such as Si and Ge, new concepts and new designs for high performance photodetectors have been developed.For example, the absorption region for a specific spectral range can be con‐ fined to a limited inner layer, avoiding typical high recombination rates of charge carriers at

Recently InGaAs/InP avalanche photodiodes (APDs) with a SAM (separation of absorption and multiplication) configuration have become commercially available. The SAM configura‐ tion is thought to be necessary for high performance APDs utilizing long wavelengths.

InGaAs/InPphotodetectors are used for maintaining the scale of spectral responsitivityup to 1.7 μm in many laboratories [17, 19].In addition they are exploited in instruments for meas‐ uring optical radiation within the near infrared (NIR) range (800 nm -1600 nm). From this point of view, these photodiodes are like other and their response is given by equations (1) and (2). Therefore to know their reflectance and internal quantum efficiency is the key for

Next experimental values for those properties measured in our laboratory for devices built

To realize our experiments related to measuring the reflectance of InGaAs/InP photodiodes

An incandescence lamp is the white light source imaged at the input slit of the monochro‐ mator. This lamp was able to cover the spectral range from 800 nm to 1600 nm and appro‐ priate blocking filters for second – order wavelengths were added to the monochromator. After the monochromator, a linear polarizer and a beam splitter, which serves to monitor temporal power fluctuations,were placed. A germanium photodiode was used as the moni‐

The experimental set-up included an optical system of mirrors, which consists of two parts. An upper part (see mirror 7 and germanium photodiode 9) realized monitoring temporal fluctuations of light power. A bottom part (see mirrors 8, 11; InGaAs/InP-photodiode 10,

the first interfaceof the photodiode and getting a higher internal quantum efficiency.

placed germanium in almost every application.

180 Photodiodes - From Fundamentals to Applications

defining the spectral responsivity scale in this range.

**8. Measurement of InP photodiode's reflectance**

the experimental set-up presented in figure 4 hasbeen arranged.

toring reference photodetector. More details can be seen in reference [20].

by different manufacturers will be presented.

the InGaAs/InP, *I <sup>m</sup> (λ)*is the response to the light reflected by the mirror, and ρm(λ) is the reflectance of a standard mirror. With this method the reflectance of photodiodes from dif‐ ferent manufacturers hasbeen measured. One part of detectors had a round active area of 5 mm in diameter and the other part had a quadratic active area of 8 mm x 8 mm.

#### **9. Analysis of Reflectance of InP Photodiodes**

The polarization degree of light at the output the monochromator was different with vary‐ ing the wavelength.The figures 5and 6 illustrate spectral dependences of the reflectance, which had been obtained from photodetectors belonging to three different manufacturers. Two types (photodiodes 1 and 4 and photodiodes 2 and 5) are 5 mm in diameter sensitive area and the third is an 8 mm in diameter sensitive area especially commercialized some years ago for developing spectral responsivity scales and no longer available in the market. Figure 5a, and 5b show that the reflectance of 5 mm in diameter detectors from both manu‐ facturers has got a minimum in the region 1000 nm to 1600 nm, and they both are related to a structure of layers providing maximal responses in the spectral interval of mayor utility of these detectors in near IR:Optics communication [17]. The first photodiode, see Figure 5a, whose reflectance was minimized, is more efficient that the second one, see figure 5b.

was produced by another manufacturer. One can remark that maybe it was produced with‐ out good enough control, because the structure of layers on the sensitive surface modi‐

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800 1000 1200 1400 1600

800 1000 1200 1400 1600

Wavelenght (nm)

The spectrum of reflectance for photodiodes 1 and 4, manufactured by the same company, is presents in figure 7. The reflectance was measured with linearly polarized and non-polar‐

Wavelenght (nm)

fies the reflectance.

0.26

0.00

**Figure 7.** Spectrum of reflectance for photodiodes 1 and 4 from the same manufacturer.

0.05

0.10

Reflectance

0.15

0.20

0.25

0.28

0.30

Reflectance

**Figure 6.** Detector with a rectangular aperture of 8 x 8mm

0.32

0.34

0.36

**Figure 5.** Detector with an active area 5 mmin diameter

Reflectance in figure 6 is associated with a photodiode with rectangular active area. In this case the reflectance has two minima at 1000 nm and 1600 nm, but the reflectance has a maximum between these minima. This photodiode is older than previous ones, and it

was produced by another manufacturer. One can remark that maybe it was produced with‐ out good enough control, because the structure of layers on the sensitive surface modi‐ fies the reflectance.

**Figure 6.** Detector with a rectangular aperture of 8 x 8mm

area and the third is an 8 mm in diameter sensitive area especially commercialized some years ago for developing spectral responsivity scales and no longer available in the market. Figure 5a, and 5b show that the reflectance of 5 mm in diameter detectors from both manu‐ facturers has got a minimum in the region 1000 nm to 1600 nm, and they both are related to a structure of layers providing maximal responses in the spectral interval of mayor utility of these detectors in near IR:Optics communication [17]. The first photodiode, see Figure 5a,

whose reflectance was minimized, is more efficient that the second one, see figure 5b.

Reflectance in figure 6 is associated with a photodiode with rectangular active area. In this case the reflectance has two minima at 1000 nm and 1600 nm, but the reflectance has a maximum between these minima. This photodiode is older than previous ones, and it

**Figure 5.** Detector with an active area 5 mmin diameter

182 Photodiodes - From Fundamentals to Applications

**Figure 7.** Spectrum of reflectance for photodiodes 1 and 4 from the same manufacturer.

The spectrum of reflectance for photodiodes 1 and 4, manufactured by the same company, is presents in figure 7. The reflectance was measured with linearly polarized and non-polar‐ ized lights, and these pair of measurements gives quite similar results. In fact, the difference was equal to approximately 2% for the angle of incidence used in this work. The same re‐ sults are depicted for the photodiodes 2 and 5, manufactured by a second company. It is im‐ portant that the results do not depend on the polarization state of the incident light when the angle of incidence is smaller than 10 degrees [22].

All spectrums of reflectance are presented in Figure 9, with linearly polarized and non po‐ larized light, so that it is possible to see the different behavior of the photodiodes in the near infrared wavelength. In fact, in this chapter we are studying the behavior of the photodetec‐ tors in the near infrared with the linearly polarized and non polarized light in the case of the polarized light the angle of incidence is smaller 10 angular degrees and is possible to ob‐

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**10. New Quantum Internal Efficiency Model of some InPphotodetectors.**

To determine the internal quantum efficiency of a photodiode it is necessary to know its re‐ sponsivity (2). In this work, the responsivity, R(λ), was measured by direct comparison to an electrically calibrated pyroelectric radiometer (ECPR), obtaining responsivity values with an uncertainty of 1.2 % approximately, roughly the uncertainty of the ECPR. Spectral respon‐ sivity values of one photodiode from every manufacturer obtained from measurements are shown in figure 10 (analogous results are obtained for the other photodiode from the same manufacturer). From now on, the photodiodes will be identified as Ham, GPD and POL. Ham and GPD are photodiodes from different manufacturers and were identified before as photodiode 2 and photodiode 1, respectively. Both have got a 5 mm in diameter active area. Photodiode POL was identified before as photodiode 4 and has got an 8 mm side square ac‐ tive area. Figure 10 shows there is a noticeable difference in responsivity between them.

serve the reflectance doesn't change its spectral behavior.

**Figure 10.** Spectral responsivity values of InPphotodiodes.

It is obtained from the responsivity values according to the equation:

**10.1. External quantum efficiency**

**Figure 8.** Spectrum of reflectance of photodiodes 2 and 5 from the same manufacturer.

**Figure 9.** Comparison of reflectance of all photodiodes measured in this work.

All spectrums of reflectance are presented in Figure 9, with linearly polarized and non po‐ larized light, so that it is possible to see the different behavior of the photodiodes in the near infrared wavelength. In fact, in this chapter we are studying the behavior of the photodetec‐ tors in the near infrared with the linearly polarized and non polarized light in the case of the polarized light the angle of incidence is smaller 10 angular degrees and is possible to ob‐ serve the reflectance doesn't change its spectral behavior.

#### **10. New Quantum Internal Efficiency Model of some InPphotodetectors.**

To determine the internal quantum efficiency of a photodiode it is necessary to know its re‐ sponsivity (2). In this work, the responsivity, R(λ), was measured by direct comparison to an electrically calibrated pyroelectric radiometer (ECPR), obtaining responsivity values with an uncertainty of 1.2 % approximately, roughly the uncertainty of the ECPR. Spectral respon‐ sivity values of one photodiode from every manufacturer obtained from measurements are shown in figure 10 (analogous results are obtained for the other photodiode from the same manufacturer). From now on, the photodiodes will be identified as Ham, GPD and POL. Ham and GPD are photodiodes from different manufacturers and were identified before as photodiode 2 and photodiode 1, respectively. Both have got a 5 mm in diameter active area. Photodiode POL was identified before as photodiode 4 and has got an 8 mm side square ac‐ tive area. Figure 10 shows there is a noticeable difference in responsivity between them.

**Figure 10.** Spectral responsivity values of InPphotodiodes.

#### **10.1. External quantum efficiency**

ized lights, and these pair of measurements gives quite similar results. In fact, the difference was equal to approximately 2% for the angle of incidence used in this work. The same re‐ sults are depicted for the photodiodes 2 and 5, manufactured by a second company. It is im‐ portant that the results do not depend on the polarization state of the incident light when

800 1000 1200 1400 1600

Wavelenght (nm)

800 1000 1200 1400 1600

Wavelenght (nm)

the angle of incidence is smaller than 10 degrees [22].

184 Photodiodes - From Fundamentals to Applications

0.06

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

**Figure 9.** Comparison of reflectance of all photodiodes measured in this work.

Reflectance

**Figure 8.** Spectrum of reflectance of photodiodes 2 and 5 from the same manufacturer.

0.08

0.10

Reflectance

0.12

0.14

0.16

0.18

It is obtained from the responsivity values according to the equation:

$$Q(\mathcal{A}) = \frac{R(\mathcal{A}) \, hc}{\mathcal{A} \, e} \tag{7}$$

**10.2. Internal quantum efficiency**

POL has particularly got a different structure.

by the manufacturer to spectrally adjust the device's reflectance.

ciency of carriers in every region given by a constant value: Pf

a

aa

**Table 2.** Parameters fitting the model to experimental internal quantum efficiency

thickness for the diode, ε (λ) can be calculated by [23]:

*f*

based on InP photodiodes in the future.

e l

Internal quantum efficiency is obtained from responsivity and reflectance by using (2). However those quantities have been measured at some wavelengths only, then it is necessa‐ ry to develop a model to interpolate them at every wavelength within the response range. To develop such a model it is necessary to know the internal structure of the photodiode, as it was done for the silicon photodiode, but a enough precise structure is not available in the open literature. Since a structure has to be assumed to develop the model, the simplest one from literature has been adopted in this work (Fig. 12). It is more than likely that detector

The first layer made on NSi is transparent in the wavelength range considered in this work. Probably it is placed in the photodiode as a passivation layer. Its thickness may be tailored

Considering a structure as shown before (Fig. 12) and a simple model for the collection effi‐

gion, 1 in the depletion region (mainly InGaAs) and Pb in the back region, and an "infinite"

( ) ( ) ( ) ( ) 1 exp exp exp exp

Where T is the thickness at which collection efficiency becomes 1, T' is the thickness at which InGaAs region starts, D' is the the thickness at which the InP (S) starts and D is the thickness at which depletion region ends. By fitting this model to internal quantum efficien‐

Internal quantum efficiency values calculated from responsivity and reflectance (dots) and adjusted values following (8) are shown in figures1 3 and 14 for photodiodes HAM and GPD, respectively. It can be seen that photodiode GPD has got an internal quantum efficien‐ cy very close to unity in the region from 1 μm to 1.6 μm, approximately. Both photodiodes have got internal quantum efficiency in this region nearly independent of wavelength. These two results are very important in order to try to develop an absolute radiometer

*D D PD*

aa

*P T TT T*

= - - + -- - + - ¢ ¢¢

*b*


( ) ( ( )) ( ) ( ) ( )

exp exp exp 1 exp

cy values, the following parameters are obtained for every photodiode [23].

**Photodiode Pf T T' D' D Pb** HAM 0 0.44 2.19 2.19 11.96 0.844 GPD 0 0.32 1.65 1.62 4351.16 0.960

,lower than 1 in the first re‐

 a

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 a

Where *h*, *c* and *e* are the usual physical constants andλis the wavelength.Values ob‐ tained are presented in figure 11 for the same detectors as before. It can be clearly seen that the oldest detector (identified as POL) presents a lower external quantum ef‐ ficiency than the other and that detector GPD presents a higher external quantum effi‐ ciency than detector HAM, which starts to decrease its quantum efficiency at a shorter wavelength. However, detector POL decreases less its quantum efficiency at wave‐ lengths lower than the corresponding to the InGaAs gap. Perhaps this is mainly due to the tailoring of the hetero-structure done by the manufacturer. Detector POL was de‐ veloped for realizing spectral responsivity scales, while the other two were developed for a better performance in the optical communications spectral range.

**Figure 11.** Spectral external quantum efficiency obtained from responsivity values

**Figure 12.** Internal Structure used in this work to model internal quantum efficiency of InP photodiodes

#### **10.2. Internal quantum efficiency**

( ) *R hc* ( ) *<sup>Q</sup>*

l

186 Photodiodes - From Fundamentals to Applications

for a better performance in the optical communications spectral range.

**Figure 11.** Spectral external quantum efficiency obtained from responsivity values

**Figure 12.** Internal Structure used in this work to model internal quantum efficiency of InP photodiodes

*e* l

<sup>=</sup> (7)

l

Where *h*, *c* and *e* are the usual physical constants andλis the wavelength.Values ob‐ tained are presented in figure 11 for the same detectors as before. It can be clearly seen that the oldest detector (identified as POL) presents a lower external quantum ef‐ ficiency than the other and that detector GPD presents a higher external quantum effi‐ ciency than detector HAM, which starts to decrease its quantum efficiency at a shorter wavelength. However, detector POL decreases less its quantum efficiency at wave‐ lengths lower than the corresponding to the InGaAs gap. Perhaps this is mainly due to the tailoring of the hetero-structure done by the manufacturer. Detector POL was de‐ veloped for realizing spectral responsivity scales, while the other two were developed

Internal quantum efficiency is obtained from responsivity and reflectance by using (2). However those quantities have been measured at some wavelengths only, then it is necessa‐ ry to develop a model to interpolate them at every wavelength within the response range. To develop such a model it is necessary to know the internal structure of the photodiode, as it was done for the silicon photodiode, but a enough precise structure is not available in the open literature. Since a structure has to be assumed to develop the model, the simplest one from literature has been adopted in this work (Fig. 12). It is more than likely that detector POL has particularly got a different structure.

The first layer made on NSi is transparent in the wavelength range considered in this work. Probably it is placed in the photodiode as a passivation layer. Its thickness may be tailored by the manufacturer to spectrally adjust the device's reflectance.

Considering a structure as shown before (Fig. 12) and a simple model for the collection effi‐ ciency of carriers in every region given by a constant value: Pf ,lower than 1 in the first re‐ gion, 1 in the depletion region (mainly InGaAs) and Pb in the back region, and an "infinite" thickness for the diode, ε (λ) can be calculated by [23]:

$$\begin{aligned} \varepsilon(\lambda) &= P\_f \left( 1 - \exp(-\alpha T) \right) + \exp(-\alpha T) - \exp(-\alpha T') + \exp(-\alpha' T')\\ &- \exp(-\alpha' D') - \exp(-\alpha D') + \exp(1 - P\_b) \exp(-\alpha D) \end{aligned} \tag{8}$$

Where T is the thickness at which collection efficiency becomes 1, T' is the thickness at which InGaAs region starts, D' is the the thickness at which the InP (S) starts and D is the thickness at which depletion region ends. By fitting this model to internal quantum efficien‐ cy values, the following parameters are obtained for every photodiode [23].


**Table 2.** Parameters fitting the model to experimental internal quantum efficiency

Internal quantum efficiency values calculated from responsivity and reflectance (dots) and adjusted values following (8) are shown in figures1 3 and 14 for photodiodes HAM and GPD, respectively. It can be seen that photodiode GPD has got an internal quantum efficien‐ cy very close to unity in the region from 1 μm to 1.6 μm, approximately. Both photodiodes have got internal quantum efficiency in this region nearly independent of wavelength. These two results are very important in order to try to develop an absolute radiometer based on InP photodiodes in the future.

The model does not fit well in the short wavelength region. Possibly this is because the structure of the detector is actually more complex or, perhaps, refraction index are not accu‐ rately known.

fraction index of the materials and thickness of the layers have to be known for interpolation. Refraction index has been obtained from [13] and other sources cited in there

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189

Thickness of the different layers is obtained by a nonlinear fitting of the experimental values of reflectance to a multilayer model. The model did not worked out well for pho‐ todiode POL, then results are not given for it. Perhaps its structure is very different from that of figure 12. Table 3 shows the thickness obtained from the fitting for photo‐ diodes Ham and GPD. The last layer, the deeper one regarding light absorption, was

Silicon photodiodes in the visible up to 950 nm and InP/InGaAs photodiodes in the NIR up to 1.6 μm are widely used for optical radiation measurements in many different applications because of their good radiometric properties. They have got high internal quantum efficien‐

Perhaps in a near future a model be developed for the internal quantum efficiency of InP/ InGaAs photodiode as it was done for the silicon, so that its responsivity may be accurately

**Photodiode NSi InP (Zn) InGaAs** HAM 162.17nm 1213.35nm 1593.2nm GPD 159.99nm 1200.54nm 1536.7nm

cy, therefore they are very useful for realizing spectral responsivity scales.

and are shown in figure 15.

**Figure 15.** Materials' refraction Index

considered to be infinite.

**12. Conclusions**

**Table 3.** Thickness of layers of InGaAs photodiodes

**Figure 13.** Internal quantum efficiency of photodiode HAM experimental values (dots) and fitted values (solid line) according to the model shown below.

**Figure 14.** Internal quantum efficiency of photodiodes GPD experimental values (dots) and fitted values (solid line) according to the model shown below.

#### **11. Interpolation of spectral reflectance**

Finally, to have the spectral responsivity scale, it is necessary to interpolate spectral reflec‐ tance at any wavelength, what can be done by using a multilayer model [11]. Complex re‐ fraction index of the materials and thickness of the layers have to be known for interpolation. Refraction index has been obtained from [13] and other sources cited in there and are shown in figure 15.

**Figure 15.** Materials' refraction Index

The model does not fit well in the short wavelength region. Possibly this is because the structure of the detector is actually more complex or, perhaps, refraction index are not accu‐

**Figure 13.** Internal quantum efficiency of photodiode HAM experimental values (dots) and fitted values (solid line)

**Figure 14.** Internal quantum efficiency of photodiodes GPD experimental values (dots) and fitted values (solid line)

Finally, to have the spectral responsivity scale, it is necessary to interpolate spectral reflec‐ tance at any wavelength, what can be done by using a multilayer model [11]. Complex re‐

rately known.

188 Photodiodes - From Fundamentals to Applications

according to the model shown below.

according to the model shown below.

**11. Interpolation of spectral reflectance**

Thickness of the different layers is obtained by a nonlinear fitting of the experimental values of reflectance to a multilayer model. The model did not worked out well for pho‐ todiode POL, then results are not given for it. Perhaps its structure is very different from that of figure 12. Table 3 shows the thickness obtained from the fitting for photo‐ diodes Ham and GPD. The last layer, the deeper one regarding light absorption, was considered to be infinite.


**Table 3.** Thickness of layers of InGaAs photodiodes

#### **12. Conclusions**

Silicon photodiodes in the visible up to 950 nm and InP/InGaAs photodiodes in the NIR up to 1.6 μm are widely used for optical radiation measurements in many different applications because of their good radiometric properties. They have got high internal quantum efficien‐ cy, therefore they are very useful for realizing spectral responsivity scales.

Perhaps in a near future a model be developed for the internal quantum efficiency of InP/ InGaAs photodiode as it was done for the silicon, so that its responsivity may be accurately known in their spectral interval of response. Some more work is also needed to know the structure of the device and improve the fitting of reflectance via a multilayer model.

[10] E.F. Zalewski and J. Geist "Silicon photodiode absolute spectral response self-calibra‐

Photodiodes as Optical Radiation Measurement Standards

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[11] Born M. and Wolf E. 1989 "Principles of Optics. Electromagnetic Theory of Propaga‐ tion, Interference and Diffraction of Light". 6th ed. *(Oxford: Pergamon)* p 633.

[12] Haapalinna A., Karha P. and Ikonen E. "Spectral reflectance of silicon photodiodes".

[13] Palik E.D. 1985 Handbook of Optical Constants of Solids. *(New York: Academic Press)*.

[14] Geist J. and Baltes H. "High accuracy modeling of photodiode quantum efficiency".

[15] Werner L, Fischer J, Johannsen U. and Hartmann J. "Accurate determination of the spectral responsivity of silicon trap detectors between 238 nm and 1015 nm using a

[16] O. Wada, H. Hasegawa, *InP-Based materials and devices : physics and technology. New*

[17] P. Corredera, M.L. Hernanz, M. González-Herráez, J. Campos "Anomalous non-line‐ ar behaviour of InGaAs photodiodes with overfilled illumination". *IOP Metrología* 40,

[18] P. Corredera, M.L. Hernanz, J. Campos, A. Corróns, A. Pons and J.L Fontecha. "Com‐ parison between absolute thermal radiometers at wavelengths of 1300 nm and 1550

[19] J M Coutin, F. Chandoul, J. Bastie,"Characterization of new trap detectors as transfer standards". *Proceedings of the 9th international conference on new developments and appli‐*

[20] A.L. Muñoz Zurita, J. Campos Acosta, A. PonsAglio. A.S. Shcherbakov. "Medida de la reflectancia de fotodiodos de InGaAs/InP". *Óptica Pura y Aplicada (Spain)*, 40(1),

[21] Campos, J. Fontecha, J. Pons, A. Corredera, P. Corróns, A., Measurement of standar‐ daluminiummirrors, reflectance versus light polarization. *Measurement Science and*

[22] A.L. Muñoz Zurita, J. Campos Acosta, A. S. Shcherbakov, A. Pons Aglio, "Differen‐ ces of silicon photodiodes reflectance among a batch and by ageing". *Optoelectronics*

[23] Ana Luz Muñoz Zurita1, Joaquín Campos Acosta2, Ramón Gómez Jimenez1, Rodri‐ go Uribe Valladares1. "AN ABSOLUTE RADIOMETER BASED ON In PPHOTODI‐

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105-109 (2007).

*Letters*. 4(5), (2008).

#### **Author details**

Ana Luz Muñoz Zurita1 , Joaquín Campos Acosta2 , Alejandro Ferrero Turrión2 and Alicia Pons Aglio2

1 Universidad Autónoma de Coahuila, Campus Torreón, Faculty of Enginering Mechanical and electrical. Torreón, Coahuila, México

2 Consejo Superior de Investigaciones Científicas (CSIC), Instituto de óptica "Daza de Valdés", Madrid, España

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known in their spectral interval of response. Some more work is also needed to know the

1 Universidad Autónoma de Coahuila, Campus Torreón, Faculty of Enginering Mechanical

2 Consejo Superior de Investigaciones Científicas (CSIC), Instituto de óptica "Daza de

[1] Ferrero, J. Campos, A. Pons, and A. Corrons "New model for the internal quantum efficiency of photodiodes based on photocurrent analysis". *Applied Optics*, Vol. 44, Is‐

[2] Gentile T.R., Houston J.M., and Cromer C.L. "Realization of a scale of absolute spec‐ tral response using the National Institute of Standards and Technology High-accura‐

[3] J. Campos, A. Corróns, A. Pons, P. Corredera, J.L. Fontecha and J.R Jiménez "Spectral responsivity uncertainty of silicon photodiodes due to calibration spectral band‐

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[7] E.F. Zalewski and C.R. Duda"Silicon photodiode device with 100% external quantum

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, Alejandro Ferrero Turrión2

and

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, Joaquín Campos Acosta2

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**Author details**

Alicia Pons Aglio2

**References**

Ana Luz Muñoz Zurita1

190 Photodiodes - From Fundamentals to Applications

Valdés", Madrid, España

and electrical. Torreón, Coahuila, México

sue 2, 208-216 (2005).


**Section 3**

**Device Applications**

**Device Applications**

**Chapter 6**

**Si-Based ZnO Ultraviolet Photodiodes**

Semiconductor-based ultraviolet (UV) photodiodes have been continuously developed that can be widely used in various commercial, civilian areas, and military applications, such as optical communications, missile launching detection, flame detection, UV radiation calibra‐ tion and monitoring, chemical and biological analysis, optical communications, and astro‐ nomical studies, etc. [1-2]. All these applications require very sensitive devices with high responsivity, fast response time, and good signal-to-noise ratio is common desirable charac‐ teristics. Currently, light detection in the UV spectral range still uses Si-based optical photo‐ diodes. Due to the Si-based photodiodes are sensitive to visible and infrared radiation, the responsivity in the UV region is still low [3-5]. To avoid these disadvantages, wide-bandgap materials (such as diamond, SiC, III-nitrides and wide-bandgap II–VI materials) are under intensive studies to improve the responsivity and stability of UV photodiodes, because of

Among them, zinc oxide (ZnO) is another wide direct bandgap material due to its sensitive and UV photoresponse in the UV region [7-9]. ZnO has attracted attention as a promising ma‐ terial for optical devices, owing to its large direct band gap energy of 3.37 eV and a large ex‐ citon binding energy of 60 meV at room temperature compared to other II-VI semiconductors [10-12]. Therefore, ZnO is promising for use in light-emitting diodes (LEDs), laser diodes (LDs), ultraviolet (UV) detection devices [12-15]. Several deposition methods have been em‐ ployed for the growth of ZnO layers, including metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), sol-gel and spray pyrolysis [16-20]. The synthesis of *p*-type ZnO films with acceptable stability and reproduci‐

> © 2012 Chen; 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,

© 2012 Chen; 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.

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Lung-Chien Chen

**1. Introduction**

http://dx.doi.org/10.5772/48825

their intrinsic visible-blindness [6].
