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The avalanche drift diode—A back illumination drift silicon photomultiplier
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015 www.elsevier.com/locate/nima
The avalanche drift diode—A back illumination drift silicon photomultiplier Jelena Ninkovic´a,b,, Rouven Eckhartb,c, Robert Hartmannb,c, Peter Hollb,c, Christian Koitschb,c, Gerhard Lutza,b, Christine Mercka,b, Razmik Mirzoyana, Hans-Gu¨nther Mosera,b, Adam-Nepomuk Ottea,b, Rainer Richtera,b, Gerhard Schallerc,d, Florian Schopperc,d, Heike Soltaub,c, Masahiro Teshimaa, George Vaˆlceanub,d a
Max-Planck-Institut fu¨r Physik, Fo¨hringer Ring 6, D-80805 Munich, Germany Max-Planck-Institut Halbleiterlabor, Otto-Hahn-Ring 6, D-81739 Munich, Germany c PNSensor GmbH, Ro¨merstr. 28, D-80803 Munich, Germany d Max-Planck-Institut fu¨r extraterrestrische Physik, GiessenbachstraX e, D-85748 Garching, Germany b
Available online 30 June 2007
Abstract Development of high quantum efficiency photon detectors is needed for many low light level (LLL) applications. Recently a new type of photodetector was introduced, the so-called Silicon PhotoMultiplier (SiPM). Its good characteristics (fast response, high gain and single photon resolution capability) make SiPM suitable for many applications. Yet its quantum efficiency is still not satisfactory ðo40%Þ for LLL applications. A new detector concept is presented that promises very high ð480%Þ quantum efficiency in a wide wavelength range (300–1000 nm). Combining the drift diode with an avalanche structure placed on the opposite side of the large-area radiation entrance window on the fully depleted bulk, one obtains a large-area device that focuses the photoelectron onto a small ‘‘pointlike’’ avalanche region. Engineering of the shallow radiation entrance window provides high quantum efficiency in the desired wavelength range. Such a device can be used as a building block for a ‘‘silicon photomultiplier’’. Extensive simulations have demonstrated the validity of this concept. A production of test devices for the optimization and characterization of avalanche regions and technology parameters has been carried out. The first results from this ‘‘proof of principle’’ production are presented. r 2007 Elsevier B.V. All rights reserved. PACS: 85.60.Gz; 95.55.Aq; 42.50.Ar Keywords: Single photon counting; High quantum efficiency; SiPM
1. Introduction The motivation to develop detectors with high quantum efficiency capable of time resolved imaging of optical single photons comes from experimental particle physics, astrophysics and many other areas. High energy particle showers generated by cosmic radiation are to be reconstructed in experiments like MAGIC [1] and EUSO [2] by observing Cherenkov and fluorescence light. The detectors used so far or considered for future experiments, Corresponding author. Max-Planck-Institut fur Physik, Fo¨hringer ¨
Ring 6, D-80805 Munich, Germany. Tel.: +49 89 83940049. E-mail address: [email protected] (J. Ninkovic´). 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.06.060
photomultipliers and Hybrid Photo Diodes, respectively have low quantum efficiency ðQE25%Þ especially in the interesting UV range. Within the framework of MAGIC experiment we are developing a new detector concept that promises high quantum efficiency in a wide wavelength range.
2. The back illumination drift silicon photomultiplier concept The Back Illumination Drift Silicon PhotoMultiplier (BID-SiPM) consists (like the existing Silicon Photomultipliers—SiPM [3]) of many small-area avalanche diodes
ARTICLE IN PRESS J. Ninkovic´ et al. / Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015
working in the limited Geiger mode. Each of these microcells provides a standard pulse when an avalanche is initiated by one (or several) electron(s). Composing several of these micro-cells to a macro-cell, by adding their signals, provides a measure for the number of photons detected by the macro-cell. The quantum efficiency of front illuminated SiPMs is limited by the insensitive regions between the micro-cells and by the presence of optically absorbing material needed for connections and circuitry on top of the radiation entrance side. In the new concept radiation enters from the backside of a fully depleted wafer and the photoelectrons are focused onto a small ‘‘point-like’’ avalanche region located on the front side (Fig. 1). A large shallow homogeneous diode on the fully depleted n-type wafer forms the radiation entrance window. The avalanche structure is formed by the nþ -doped anode and the buried p-type layer (deep-p) which is connected laterally to the innermost pþ -doped ring ðR0 Þ. The doping of the buried layer has to be chosen in such a way that avalanche condition is reached when it is fully depleted by applying a sufficiently high reverse bias voltage between anode (A) and R0 . In order to suppress high electric fields in the edge regions of the anode the buried p-layer varies in depth. The negatively biased drift rings R1 , R2 will focus the photoelectrons towards the center avalanche region. A buried n-layer prevents injection of holes from the deep-p to the back side and improves focusing time properties. Results from the extended device simulations performed up to now can be found in Refs. [5,6]. In this new photon detector concept [4–6] the 100% fill factor of the radiation entrance window leads to higher quantum efficiency compared to the front illuminated SiPMs. Additionally, the homogeneous radiation entrance window allows deposition of different antireflective coatings and optical filters to optimize for a specific application [7,8]. Simulation of different UV enhanced antireflective coatings is shown in Fig. 2. Extremely high quantum efficiency in a wide wavelength range makes this device unique and ideal for many applications.
Fig. 1. Concept of the BID-SiPM (not to scale).
Fig. 2. Simulated quantum efficiency for different antireflective coatings.
10 modulated HF region + deep n modulated HF region no deep n no modulation + deep n no modulation no deep n
8 Current [µA]
1014
6
4
2
0 0
10
20
30
40
50
60
70
80
Voltage [V] Fig. 3. Breakdown voltages of single cells measured with 1 MO resistor. Different designs of cells are indicated with different line types.
3. Results from the first test production In order to study and optimize the avalanche region in the first iteration, front illuminated test devices have been produced (no backside treatment and no drift structures). In our design we have tested four different design combinations: devices with flat deep p-layer with and without deep n-layer and devices whose deep p-layer varies in depth (modulated high field (HF) region) with and without deep n-layer. All four combinations have been simulated and measured values are in good agreement with expected values from simulations. Results are summarized in Fig. 3. We have tested homogeneity of the leakage current and the measurements showed high homogeneity over several millimeters (Fig. 4). Finally in order to demonstrate reproducibility and separation of relevant bulk leakage current from not amplified edge current, we have measured diodes with constant area but different circumferences. Bulk current of 1:26ð2Þ pA=mm2 has been determined (Fig. 5).
ARTICLE IN PRESS J. Ninkovic´ et al. / Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015
0
Current [pA]
-2
-4
-6
-8 -30
-25
-20
-15 Voltage [V]
-10
-5
0
1015
energy range of optical photons. This is due to placing the thin homogeneous entrance window on the backside of a fully depleted silicon substrate and the focusing of the electrons generated by radiation into a small (point-like) avalanche region. The latter is accomplished with the help of a drift diode structure. The new structure can be used as building block for a ‘‘Silicon Photomultiplier’’ (SiPM). Extended simulations have shown the validity of the concept. In a first step simple test structures have been produced that allow verification of the parameters which entered into the device simulations. Preliminary results of these proof-of-principle production are encouraging and thus it will be followed by production of complete detectors. The devices will be produced in the MPI Semiconductor Laboratory. The results from the first prototype production are expected in 2007.
Fig. 4. Homogeneity of leakage current of five identical diodes distributed over a distance of 7 mm.
References
-4.0 -3.5
[1] [2] [3] [4]
Current [pA]
-3.0 -2.5 -2.0
[5] [6] [7]
-1.5 -1.0
[8]
-0.5 0.0 0
2
4
6
8
10
12
14
16
18
20
Circumference [mm] Fig. 5. Series of diodes with identical area ð1 mm2 Þ and different circumferences have been measured in order to separate bulk leakage current from not amplified edge current. Measured currents (0–10 V) have been averaged for identical diodes and bulk current of 1:26ð2Þ pA=mm2 has been determined as extrapolation to zero circumference. Small error bars demonstrate good homogeneity.
4. Conclusions Our new concept of the BID-SiPM structure promises high photon detection efficiency ð480%Þ over the full
MAGIC experiment, hhttp://magic.mppmu.mpg.de/i. EUSO experiment, hhttp://www.euso-mission.org/i. B. Dolgoshein, et al., Nucl. Instr. and Meth. A 504 (2003) 48. G. Lutz, R.H. Richter, L. Strueder, Avalanche Strahlungsdetektor, German patent DE 102004022948. G. Lutz, et al., IEEE Trans. Nucl. Sci. NS-52 (2005) 1156. G. Lutz, et al., Nucl. Instr. and Meth. A 567 (2006) 129. R. Hartmann, K. Stephan, L. Strueder, Nucl. Instr. and Meth. A 439 (2000) 216. R. Hartmann, et al., Proc. SPIE 5903 (2005) N1.
Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015 www.elsevier.com/locate/nima
The avalanche drift diode—A back illumination drift silicon photomultiplier Jelena Ninkovic´a,b,, Rouven Eckhartb,c, Robert Hartmannb,c, Peter Hollb,c, Christian Koitschb,c, Gerhard Lutza,b, Christine Mercka,b, Razmik Mirzoyana, Hans-Gu¨nther Mosera,b, Adam-Nepomuk Ottea,b, Rainer Richtera,b, Gerhard Schallerc,d, Florian Schopperc,d, Heike Soltaub,c, Masahiro Teshimaa, George Vaˆlceanub,d a
Max-Planck-Institut fu¨r Physik, Fo¨hringer Ring 6, D-80805 Munich, Germany Max-Planck-Institut Halbleiterlabor, Otto-Hahn-Ring 6, D-81739 Munich, Germany c PNSensor GmbH, Ro¨merstr. 28, D-80803 Munich, Germany d Max-Planck-Institut fu¨r extraterrestrische Physik, GiessenbachstraX e, D-85748 Garching, Germany b
Available online 30 June 2007
Abstract Development of high quantum efficiency photon detectors is needed for many low light level (LLL) applications. Recently a new type of photodetector was introduced, the so-called Silicon PhotoMultiplier (SiPM). Its good characteristics (fast response, high gain and single photon resolution capability) make SiPM suitable for many applications. Yet its quantum efficiency is still not satisfactory ðo40%Þ for LLL applications. A new detector concept is presented that promises very high ð480%Þ quantum efficiency in a wide wavelength range (300–1000 nm). Combining the drift diode with an avalanche structure placed on the opposite side of the large-area radiation entrance window on the fully depleted bulk, one obtains a large-area device that focuses the photoelectron onto a small ‘‘pointlike’’ avalanche region. Engineering of the shallow radiation entrance window provides high quantum efficiency in the desired wavelength range. Such a device can be used as a building block for a ‘‘silicon photomultiplier’’. Extensive simulations have demonstrated the validity of this concept. A production of test devices for the optimization and characterization of avalanche regions and technology parameters has been carried out. The first results from this ‘‘proof of principle’’ production are presented. r 2007 Elsevier B.V. All rights reserved. PACS: 85.60.Gz; 95.55.Aq; 42.50.Ar Keywords: Single photon counting; High quantum efficiency; SiPM
1. Introduction The motivation to develop detectors with high quantum efficiency capable of time resolved imaging of optical single photons comes from experimental particle physics, astrophysics and many other areas. High energy particle showers generated by cosmic radiation are to be reconstructed in experiments like MAGIC [1] and EUSO [2] by observing Cherenkov and fluorescence light. The detectors used so far or considered for future experiments, Corresponding author. Max-Planck-Institut fur Physik, Fo¨hringer ¨
Ring 6, D-80805 Munich, Germany. Tel.: +49 89 83940049. E-mail address: [email protected] (J. Ninkovic´). 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.06.060
photomultipliers and Hybrid Photo Diodes, respectively have low quantum efficiency ðQE25%Þ especially in the interesting UV range. Within the framework of MAGIC experiment we are developing a new detector concept that promises high quantum efficiency in a wide wavelength range.
2. The back illumination drift silicon photomultiplier concept The Back Illumination Drift Silicon PhotoMultiplier (BID-SiPM) consists (like the existing Silicon Photomultipliers—SiPM [3]) of many small-area avalanche diodes
ARTICLE IN PRESS J. Ninkovic´ et al. / Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015
working in the limited Geiger mode. Each of these microcells provides a standard pulse when an avalanche is initiated by one (or several) electron(s). Composing several of these micro-cells to a macro-cell, by adding their signals, provides a measure for the number of photons detected by the macro-cell. The quantum efficiency of front illuminated SiPMs is limited by the insensitive regions between the micro-cells and by the presence of optically absorbing material needed for connections and circuitry on top of the radiation entrance side. In the new concept radiation enters from the backside of a fully depleted wafer and the photoelectrons are focused onto a small ‘‘point-like’’ avalanche region located on the front side (Fig. 1). A large shallow homogeneous diode on the fully depleted n-type wafer forms the radiation entrance window. The avalanche structure is formed by the nþ -doped anode and the buried p-type layer (deep-p) which is connected laterally to the innermost pþ -doped ring ðR0 Þ. The doping of the buried layer has to be chosen in such a way that avalanche condition is reached when it is fully depleted by applying a sufficiently high reverse bias voltage between anode (A) and R0 . In order to suppress high electric fields in the edge regions of the anode the buried p-layer varies in depth. The negatively biased drift rings R1 , R2 will focus the photoelectrons towards the center avalanche region. A buried n-layer prevents injection of holes from the deep-p to the back side and improves focusing time properties. Results from the extended device simulations performed up to now can be found in Refs. [5,6]. In this new photon detector concept [4–6] the 100% fill factor of the radiation entrance window leads to higher quantum efficiency compared to the front illuminated SiPMs. Additionally, the homogeneous radiation entrance window allows deposition of different antireflective coatings and optical filters to optimize for a specific application [7,8]. Simulation of different UV enhanced antireflective coatings is shown in Fig. 2. Extremely high quantum efficiency in a wide wavelength range makes this device unique and ideal for many applications.
Fig. 1. Concept of the BID-SiPM (not to scale).
Fig. 2. Simulated quantum efficiency for different antireflective coatings.
10 modulated HF region + deep n modulated HF region no deep n no modulation + deep n no modulation no deep n
8 Current [µA]
1014
6
4
2
0 0
10
20
30
40
50
60
70
80
Voltage [V] Fig. 3. Breakdown voltages of single cells measured with 1 MO resistor. Different designs of cells are indicated with different line types.
3. Results from the first test production In order to study and optimize the avalanche region in the first iteration, front illuminated test devices have been produced (no backside treatment and no drift structures). In our design we have tested four different design combinations: devices with flat deep p-layer with and without deep n-layer and devices whose deep p-layer varies in depth (modulated high field (HF) region) with and without deep n-layer. All four combinations have been simulated and measured values are in good agreement with expected values from simulations. Results are summarized in Fig. 3. We have tested homogeneity of the leakage current and the measurements showed high homogeneity over several millimeters (Fig. 4). Finally in order to demonstrate reproducibility and separation of relevant bulk leakage current from not amplified edge current, we have measured diodes with constant area but different circumferences. Bulk current of 1:26ð2Þ pA=mm2 has been determined (Fig. 5).
ARTICLE IN PRESS J. Ninkovic´ et al. / Nuclear Instruments and Methods in Physics Research A 580 (2007) 1013–1015
0
Current [pA]
-2
-4
-6
-8 -30
-25
-20
-15 Voltage [V]
-10
-5
0
1015
energy range of optical photons. This is due to placing the thin homogeneous entrance window on the backside of a fully depleted silicon substrate and the focusing of the electrons generated by radiation into a small (point-like) avalanche region. The latter is accomplished with the help of a drift diode structure. The new structure can be used as building block for a ‘‘Silicon Photomultiplier’’ (SiPM). Extended simulations have shown the validity of the concept. In a first step simple test structures have been produced that allow verification of the parameters which entered into the device simulations. Preliminary results of these proof-of-principle production are encouraging and thus it will be followed by production of complete detectors. The devices will be produced in the MPI Semiconductor Laboratory. The results from the first prototype production are expected in 2007.
Fig. 4. Homogeneity of leakage current of five identical diodes distributed over a distance of 7 mm.
References
-4.0 -3.5
[1] [2] [3] [4]
Current [pA]
-3.0 -2.5 -2.0
[5] [6] [7]
-1.5 -1.0
[8]
-0.5 0.0 0
2
4
6
8
10
12
14
16
18
20
Circumference [mm] Fig. 5. Series of diodes with identical area ð1 mm2 Þ and different circumferences have been measured in order to separate bulk leakage current from not amplified edge current. Measured currents (0–10 V) have been averaged for identical diodes and bulk current of 1:26ð2Þ pA=mm2 has been determined as extrapolation to zero circumference. Small error bars demonstrate good homogeneity.
4. Conclusions Our new concept of the BID-SiPM structure promises high photon detection efficiency ð480%Þ over the full
MAGIC experiment, hhttp://magic.mppmu.mpg.de/i. EUSO experiment, hhttp://www.euso-mission.org/i. B. Dolgoshein, et al., Nucl. Instr. and Meth. A 504 (2003) 48. G. Lutz, R.H. Richter, L. Strueder, Avalanche Strahlungsdetektor, German patent DE 102004022948. G. Lutz, et al., IEEE Trans. Nucl. Sci. NS-52 (2005) 1156. G. Lutz, et al., Nucl. Instr. and Meth. A 567 (2006) 129. R. Hartmann, K. Stephan, L. Strueder, Nucl. Instr. and Meth. A 439 (2000) 216. R. Hartmann, et al., Proc. SPIE 5903 (2005) N1.