Cataloged from PDF version of article.The authors report high performance solar-blind photodetectors with reproducible avalanche gain as
high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff
around 276 nm. The dark currents of the 40  m diameter devices are measured to be lower than
8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272 nm
under 20 V reverse bias. The thermally limited detectivity is calculated as D*=1.4
1014 cm Hz1/2 W−1 for a 40  m diameter device

Gokkavas, M.

Inal, A.

Ozbay, E.

Tut, T.

Applied Physics Letters

Bilkent University Institutional Repository

AlxGa1−xN-based avalanche photodiodes with high reproducibleavalanche gainTurgut Tut, Mutlu Gokkavas, Ayse Inal, and Ekmel Ozbay  Citation: Appl. Phys. Lett. 90, 163506 (2007); doi: 10.1063/1.2724926 View online: http://dx.doi.org/10.1063/1.2724926 View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v90/i16 Published by the American Institute of Physics.  Additional information on Appl. Phys. Lett.Journal Homepage: http://apl.aip.org/ Journal Information: http://apl.aip.org/about/about_the_journal Top downloads: http://apl.aip.org/features/most_downloaded Information for Authors: http://apl.aip.org/authors Downloaded 07 May 2013 to 139.179.14.46. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissionsAlxGa1−xN-based avalanche photodiodes with high reproducibleavalanche gainTurgut Tut,a Mutlu Gokkavas, Ayse Inal, and Ekmel OzbayNanotechnology Research Center, Bilkent University, Bilkent, 06800 Ankara, Turkey; Department ofPhysics, Bilkent University, Bilkent, 06800 Ankara, Turkey; and Department of Electrical and ElectronicsEngineering, Bilkent University, Bilkent, 06800 Ankara, TurkeyReceived 5 December 2006; accepted 19 March 2007; published online 17 April 2007The authors report high performance solar-blind photodetectors with reproducible avalanche gain ashigh as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoffaround 276 nm. The dark currents of the 40 m diameter devices are measured to be lower than8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272 nmunder 20 V reverse bias. The thermally limited detectivity is calculated as D*=1.41014 cm Hz1/2 W−1 for a 40 m diameter device. © 2007 American Institute of Physics.DOI: 10.1063/1.2724926The recent developments in high Al-content AlxGa1−xNmaterial growth technology made it possible to fabricatehigh performance solar-blind photodetectors operating in theultraviolet UV spectral region with improved receiver sen-sitivity, low noise, low dark current density, and highspeed.1–3 AlGaN-based Schottky, p-i-n, and metal-semiconductor-metal photodetectors with very high perfor-mances have already been demonstrated.4,5 The UV-filteringnature of the atmospheric ozone molecules blocks the solarradiation to reach the earth’s surface for wavelengths shorterthan 280 nm. In this case, UV photodetectors with cutoffwavelengths around 280 nm, which are also called solar-blind detectors, can detect very weak UV signals under in-tense background radiation. These devices have importantapplications including missile plume detection, chemical/biological agent sensing, flame alarms, covert space-to-spaceand submarine communications, ozone-layer monitoring, andgas detection. Due to their high responsivity 600 A/W,high speed, high cathode gain on the order of a million, andlow dark current properties, photomultiplier tubes PMTsare frequently used in such applications. However, PMTs arevery expensive and bulky. Besides, they require a coolingsystem, and they have high operation voltages in excess of1000 V. To achieve solar-blind detection, PMTs should alsobe integrated with complex and expensive filters. In order toavoid these disadvantages, high performance solid-state UVphotodetectors with high internal gain are needed.6 Wideband-gap semiconductor photodetectors, such as AlxGa1−xNwith x=0.4, are ideal candidates for this purpose. These de-vices are intrinsically solar blind, in which no additional fil-ters are needed, they have low noise,7 and fast responsetimes.8 The lack of high internal gain has been the majorlimitation for the usage of AlGaN photodetectors for appli-cations that require high sensitivity detectors. There havebeen several theoretical research work that examined theavalanche effect in GaN and AlGaN-based structures.9–11 Ex-perimental work on both GaN Refs. 12–18 and AlGaN-based Refs. 4, 19, and 20 avalanche photodiodes APDswere also reported. However, reproducible high gain inAlGaN-based APDs is still a major limitation. In this letter,we report the realization of solar-blind AlGaN-based ava-lanche photodetectors with reproducible high avalanche gain.The epitaxial structure of the avalanche photodetector isdesigned for solar-blind operation with high avalanche gain.The Al0.4Ga0.6N absorption layer was used as a multiplica-tion layer with c=276 nm. The AlxGa1−xN epitaxial layersof our Schottky photodiode wafer were grown on a 2 in.double side polished 0001 sapphire substrate using a metal-organic chemical vapor deposition MOCVD system, whichis located at the Bilkent University Nanotechnology Re-search Center. First, a thin AlN nucleation layer was depos-ited, and then a 0.3 m thick AlN buffer layer was depos-ited. Subsequently, a highly doped n+=1.081018 cm−30.3 m thick Al0.4Ga0.6N layer was deposited for Ohmiccontact, followed by a 0.2 m thick Al0.4Ga0.6N layer withrelatively low doping n−=1.451017 cm−3 for Schottkycontact.The samples were fabricated by using a five-stepmicrowave-compatible fabrication process in a class-100clean room environment. The dry etching was accomplishedvia reactive ion etching RIE under CCl2F2 plasma, a20 SCCM SCCM denotes standard cubic centimeter perminute at STP gas flow rate, and 200 W rf power. The mesastructures of the devices were formed via the RIE process, byetching all of the layers 0.8 m down to the sapphirelayer for better mesa isolation. After an Ohmic etchof 0.3 m, Ti/Al 100 Å/1000 Å contacts were depos-ited via thermal evaporation and left in acetone solution forthe lift-off process. The contacts were annealed at 700 °C for60 s in a rapid thermal annealing system. An 100 Å thickAu metal was evaporated in order to form Au/AlGaNSchottky contacts. Thereafter, a 200 nm thick Si3N4 was de-posited via plasma enhanced chemical vapor deposition forpassivation. Finally, an 0.25 m thick Ti/Au interconnectmetal was deposited and lifted-off to connect the Schottkylayers to the coplanar waveguide transmission line pads.After fabrication, the devices were characterized interms of current-voltage and spectral responsivity. The fabri-cated devices had breakdown voltages higher than 60 V. Inorder to have better mesa isolation, we etched down to thesapphire substrate,21 which enabled us to attain low leakagecurrent. I-V measurements of the larger area devices resultedaElectronic mail: tturgut@fen.bilkent.edu.trAPPLIED PHYSICS LETTERS 90, 163506 20070003-6951/2007/9016/163506/3/$23.00 © 2007 American Institute of Physics90, 163506-1Downloaded 07 May 2013 to 139.179.14.46. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissionsin higher leakage currents. Therefore, we chose to use thesmaller area devices with 20, 40, and 60 m diameters.Current-voltage characterization of the fabricated Schottkyphotodetectors was carried out by using a Keithley 6517Ahigh resistance electrometer with low noise triax cables. Fig-ure 1 shows the dark current measurements of a 40 m di-ameter device. The dark current for a 40 m diameter deviceat 60 V reverse bias was approximately 0.3 nA. For reversebias values below 20 V, the measured dark current was lim-ited by the experimental setup and was less than 8 fA. TheHall measurements of the MOCVD grown samples showedthat the active AlGaN layer had a Si doping concentrationNd=1.451017 cm−3 and the Ohmic AlGaN layer had a Sidoping concentration Nd=1.081018 cm−3.Figure 2a shows the transmission characteristics of theas-grown epitaxial structure. The AlGaN layer absorbs allphotons with energies higher than 4.4 eV. Figure 2b showsthe responsivity measurements of a 150 m diameter device.In parallel with the transmission measurement, the respon-sivity of the fabricated device has a sharp cutoff at 276 nm,which qualifies the AlGaN photodetectors to be solar blind.Under a 20 V reverse bias voltage, the device had a maxi-mum responsivity of 0.13 A/W at 272 nm. Under 0 V bias,the device had a maximum responsivity of 12.2 mA/W at270 nm under front illumination. The UV/visible rejectionratio for wavelengths larger than 350 nm is on the order of2104 under zero bias. Thermally limited detectivity is cal-culated as D*=1.41014 cm Hz1/2 W−1 which correspondsto the highest value reported for an AlGaN-based Schottkyphotodiodes. Differential resistance at zero bias isR0=1.31016 . According to the responsivity measure-ments, the photocurrent does not significantly increase after20 V. Therefore, we set the unity gain at 20 V. From thephotocurrent and dark current data, we calculated the ava-lanche gain by first taking the difference between the multi-plied photocurrent and dark current data, and then normaliz-ing it with respect to the unmultiplied difference of thephotocurrent and dark current. The avalanche gain at a 68 Vreverse bias was 1560, which is the highest reproducible ava-lanche gain reported in the literature for AlGaN-based solar-blind APDs. We proved reproducibility by way of taking thedark current measurement after several photocurrent mea-surements, in which we saw no significant change in darkFIG. 1. Dark current measurement data from a 40 m diameter photodetec-tor device.FIG. 2. a Transmission data from a double side polished wafer which isused in the fabrication. b Responsivity measurements result from a150 m diameter device.FIG. 3. a Gain measurements for a 40 m diameter device. b Avalanchegain extracted from the photocurrent measurements.163506-2 Tut et al. Appl. Phys. Lett. 90, 163506 2007Downloaded 07 May 2013 to 139.179.14.46. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissionscurrent ten scans, and consequently, also none in the ava-lanche gain results ten scans, which is shown in Fig. 3.We determined the voltage at which the unity gain oc-curs via C-V and lock-in assisted responsivity measurements.After the 20 V bias, the capacitance does not change whichis an indicator of full depletion of the junction. Close to 20 Vthe lock-in assisted responsivity does not change consider-ably and after 20 V it does not increase steadily and signifi-cantly unlike avalanche gain which starts generally after60 V.We also measured the dark currents under different tem-peratures. In Fig. 4, the dark current of a photodetectorshows a strong dependence on temperature. This resultproves that Zener tunneling, which is a temperature insensi-tive process, is not a possible gain mechanism in these de-vices. The gain measurements showed an exponential depen-dence on voltage, in which we infer from this result that thephotoconductive gain is not a possible gain mechanism inour devices. We know that the photoconductive gain in-creases linearly with voltage.19,22 Therefore, we concludethat the gain in these devices result from the avalanche mul-tiplication of the photogenerated carriers in the active regionof the devices.In summary, we present the MOCVD growth, fabrica-tion, and characterization of AlGaN-based solar-blind APDs.The avalanche gain at 68 V was in excess of 1560 with noGeiger mode breakdown. The electric field was on the orderof 1.88 MV/cm. The gain in the active region of the devicesis attributed to the avalanche multiplication of the photoge-nerated carriers. This work demonstrates the high potentialof AlGaN APDs for replacement of the PMTs for high sen-sitive solar-blind photodetector applications.This work is supported by the European Union under theprojects EU-NoE-METAMORPHOSE, EU-NoE-PHOREMOST, and TUBITAK under Projects Nos.104E090, 105E066, 105A005, and 106A017. One of the au-thors E.O. also acknowledges partial support from theTurkish Academy of Sciences.1E. Ozbay, N. Biyikli, I. Kimukin, T. Tut, T. Kartaloglu, and O. Aytur,IEEE J. Sel. Top. Quantum Electron. 10, 742 2004.2C. J. Collins, U. Chowdhury, M. M. Wong, B. Yang, A. L. Beck, and R. D.Dupuis, Electron. Lett. 38, 824 2002.3N. Biyikli, T. Kartaloglu, O. Aytur, I. Kimukin, and E. Ozbay, Appl. Phys.Lett. 79, 2838 2001.4N. Biyikli, I. Kimukin, T. Tut, O. Aytur, and E. Ozbay, Appl. Phys. Lett.81, 3272 2002.5S. Butun, M. Gokkavas, HongBo Yu, and E. Ozbay, Appl. Phys. Lett. 89,073503 2006.6J. C. Campbell, S. Demiguel, F. Ma, A. Beck, X. Guo, S. Wang, X. Zheng,X. Li, J. D. Beck, M. A. Kinch, A. Huntington, L. A. Coldren, J. Decobert,and N. Tscherptner, IEEE J. Quantum Electron. 10, 777 2004.7T. Tut, S. Butun, B. Butun, M. Gokkavas, H. B. Yu, and E. Ozbay,Appl. Phys. Lett. 87, 223502 2005.8N. Biyikli, I. Kimukin, T. Kartaloglu, O. Aytur, and Ekmel Ozbay,Phys. Status Solidi C 7, 2314 2003.9Y. Wang, K. Brennan, and P. Ruden, IEEE J. Quantum Electron. 27, 2321991.10P. Ruden and S. Krishnankutty, IEEE Trans. Electron Devices 46, 23481999.11C. Sevik and C. Bulutay, Appl. Phys. Lett. 83, 1382 2003.12K. A. McIntosh, R. J. Molnar, L. J. Mahoney, A. Lightfoot, M. W. Geis,K. M. Molvar, I. Melngailis, R. L. Aggarwal, W. D. Goodhue, S. S. Choi,D. L. Spears, and S. Verghese, Appl. Phys. Lett. 75, 3485 1999.13J. C. Carrano, D. J. H. Lambert, C. J. Eiting, C. J. Collins, T. Li, S. Wang,B. Yang, A. L. Beck, R. D. Dupuis, and J. C. Campbell, Appl. Phys. Lett.76, 924 2000.14A. Osinsky, M. S. Shur, R. Gaska, and Q. Chen, Electron. Lett. 34, 6911998.15S. Verghese, K. A. McIntosh, R. J. Molnar, L. J. Mahoney, R. L.Aggarwal, M. W. Geis, K. M. Molvar, E. K. Duerr, and I. Melngailis,IEEE Electron Device Lett. 48, 502 2001.16K. A. McIntosh, R. J. Molnar, L. J. Mahoney, K. M. Molvar, N. Efremov,and S. Verghese, Appl. Phys. Lett. 76, 3938 2000.17B. Yang, T. Li, K. Heng, C. Collins, S. Wang, J. C. Carrano, R. D. Dupuis,J. C. Campbell, M. J. Schurman, and I. T. Ferguson, IEEE J. QuantumElectron. 36, 1389 2000.18J. B. Limb, D. Yoo, J. H. Ryou, W. Lee, S. C. Shen, R. D. Dupuis, M. L.Reed, C. J. Collins, M. Wraback, D. Hanser, E. Preble, N. M. Williams,and K. Evans, Appl. Phys. Lett. 89, 011112 2006.19R. McClintock, A. Yasan, K. Minder, P. Kung, and M. Razeghi,Appl. Phys. Lett. 87, 241123 2005.20T. Tut, M. Gokkavas, B. Butun, S. Butun, E. Ulker, and E. Ozbay,Appl. Phys. Lett. 89, 183524 2006.21T. Tut, N. Biyikli, I. Kimukin, T. Kartaloglu, O. Aytur, S. Unlu, and E.Ozbay, Solid-State Electron. 49, 117 2005.22S. M. Sze, Physics of Semiconductor Devices, 2nd ed. Wiley, New York,1981, Chap. 13, p. 744.FIG. 4. Dark current measurement data with varying temperatures.163506-3 Tut et al. Appl. Phys. Lett. 90, 163506 2007Downloaded 07 May 2013 to 139.179.14.46. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions

AlxGa1-xN-based avalanche photodiodes with high reproducible avalanche gain

The authors report high performance solar-blind photodetectors with reproducible avalanche gain as high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff around 276 nm. The dark currents of the 40 μm diameter devices are measured to be lower than 8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272 nm under 20 V reverse bias. The thermally limited detectivity is calculated as D* = 1.4 × 1014 cm Hz1/2 W-1 for a 40 μm diameter device. © 2007 American Institute of Physics

AlxGa1−xN-based avalanche photodiodes with high reproducibleavalanche gainTurgut Tut,a Mutlu Gokkavas, Ayse Inal, and Ekmel OzbayNanotechnology Research Center, Bilkent University, Bilkent, 06800 Ankara, Turkey; Department ofPhysics, Bilkent University, Bilkent, 06800 Ankara, Turkey; and Department of Electrical and ElectronicsEngineering, Bilkent University, Bilkent, 06800 Ankara, TurkeyReceived 5 December 2006; accepted 19 March 2007; published online 17 April 2007The authors report high performance solar-blind photodetectors with reproducible avalanche gain ashigh as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoffaround 276 nm. The dark currents of the 40 m diameter devices are measured to be lower than8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272 nmunder 20 V reverse bias. The thermally limited detectivity is calculated as D*=1.41014 cm Hz1/2 W−1 for a 40 m diameter device. © 2007 American Institute of Physics.DOI: 10.1063/1.2724926The recent developments in high Al-content AlxGa1−xNmaterial growth technology made it possible to fabricatehigh performance solar-blind photodetectors operating in theultraviolet UV spectral region with improved receiver sen-sitivity, low noise, low dark current density, and highspeed.1–3 AlGaN-based Schottky, p-i-n, and metal-semiconductor-metal photodetectors with very high perfor-mances have already been demonstrated.4,5 The UV-filteringnature of the atmospheric ozone molecules blocks the solarradiation to reach the earth’s surface for wavelengths shorterthan 280 nm. In this case, UV photodetectors with cutoffwavelengths around 280 nm, which are also called solar-blind detectors, can detect very weak UV signals under in-tense background radiation. These devices have importantapplications including missile plume detection, chemical/biological agent sensing, flame alarms, covert space-to-spaceand submarine communications, ozone-layer monitoring, andgas detection. Due to their high responsivity 600 A/W,high speed, high cathode gain on the order of a million, andlow dark current properties, photomultiplier tubes PMTsare frequently used in such applications. However, PMTs arevery expensive and bulky. Besides, they require a coolingsystem, and they have high operation voltages in excess of1000 V. To achieve solar-blind detection, PMTs should alsobe integrated with complex and expensive filters. In order toavoid these disadvantages, high performance solid-state UVphotodetectors with high internal gain are needed.6 Wideband-gap semiconductor photodetectors, such as AlxGa1−xNwith x=0.4, are ideal candidates for this purpose. These de-vices are intrinsically solar blind, in which no additional fil-ters are needed, they have low noise,7 and fast responsetimes.8 The lack of high internal gain has been the majorlimitation for the usage of AlGaN photodetectors for appli-cations that require high sensitivity detectors. There havebeen several theoretical research work that examined theavalanche effect in GaN and AlGaN-based structures.9–11 Ex-perimental work on both GaN Refs. 12–18 and AlGaN-based Refs. 4, 19, and 20 avalanche photodiodes APDswere also reported. However, reproducible high gain inAlGaN-based APDs is still a major limitation. In this letter,we report the realization of solar-blind AlGaN-based ava-lanche photodetectors with reproducible high avalanche gain.The epitaxial structure of the avalanche photodetector isdesigned for solar-blind operation with high avalanche gain.The Al0.4Ga0.6N absorption layer was used as a multiplica-tion layer with c=276 nm. The AlxGa1−xN epitaxial layersof our Schottky photodiode wafer were grown on a 2 in.double side polished 0001 sapphire substrate using a metal-organic chemical vapor deposition MOCVD system, whichis located at the Bilkent University Nanotechnology Re-search Center. First, a thin AlN nucleation layer was depos-ited, and then a 0.3 m thick AlN buffer layer was depos-ited. Subsequently, a highly doped n+=1.081018 cm−30.3 m thick Al0.4Ga0.6N layer was deposited for Ohmiccontact, followed by a 0.2 m thick Al0.4Ga0.6N layer withrelatively low doping n−=1.451017 cm−3 for Schottkycontact.The samples were fabricated by using a five-stepmicrowave-compatible fabrication process in a class-100clean room environment. The dry etching was accomplishedvia reactive ion etching RIE under CCl2F2 plasma, a20 SCCM SCCM denotes standard cubic centimeter perminute at STP gas flow rate, and 200 W rf power. The mesastructures of the devices were formed via the RIE process, byetching all of the layers 0.8 m down to the sapphirelayer for better mesa isolation. After an Ohmic etchof 0.3 m, Ti/Al 100 Å/1000 Å contacts were depos-ited via thermal evaporation and left in acetone solution forthe lift-off process. The contacts were annealed at 700 °C for60 s in a rapid thermal annealing system. An 100 Å thickAu metal was evaporated in order to form Au/AlGaNSchottky contacts. Thereafter, a 200 nm thick Si3N4 was de-posited via plasma enhanced chemical vapor deposition forpassivation. Finally, an 0.25 m thick Ti/Au interconnectmetal was deposited and lifted-off to connect the Schottkylayers to the coplanar waveguide transmission line pads.After fabrication, the devices were characterized interms of current-voltage and spectral responsivity. The fabri-cated devices had breakdown voltages higher than 60 V. Inorder to have better mesa isolation, we etched down to thesapphire substrate,21 which enabled us to attain low leakagecurrent. I-V measurements of the larger area devices resultedaElectronic mail: tturgut@fen.bilkent.edu.trAPPLIED PHYSICS LETTERS 90, 163506 20070003-6951/2007/9016/163506/3/$23.00 © 2007 American Institute of Physics90, 163506-1in higher leakage currents. Therefore, we chose to use thesmaller area devices with 20, 40, and 60 m diameters.Current-voltage characterization of the fabricated Schottkyphotodetectors was carried out by using a Keithley 6517Ahigh resistance electrometer with low noise triax cables. Fig-ure 1 shows the dark current measurements of a 40 m di-ameter device. The dark current for a 40 m diameter deviceat 60 V reverse bias was approximately 0.3 nA. For reversebias values below 20 V, the measured dark current was lim-ited by the experimental setup and was less than 8 fA. TheHall measurements of the MOCVD grown samples showedthat the active AlGaN layer had a Si doping concentrationNd=1.451017 cm−3 and the Ohmic AlGaN layer had a Sidoping concentration Nd=1.081018 cm−3.Figure 2a shows the transmission characteristics of theas-grown epitaxial structure. The AlGaN layer absorbs allphotons with energies higher than 4.4 eV. Figure 2b showsthe responsivity measurements of a 150 m diameter device.In parallel with the transmission measurement, the respon-sivity of the fabricated device has a sharp cutoff at 276 nm,which qualifies the AlGaN photodetectors to be solar blind.Under a 20 V reverse bias voltage, the device had a maxi-mum responsivity of 0.13 A/W at 272 nm. Under 0 V bias,the device had a maximum responsivity of 12.2 mA/W at270 nm under front illumination. The UV/visible rejectionratio for wavelengths larger than 350 nm is on the order of2104 under zero bias. Thermally limited detectivity is cal-culated as D*=1.41014 cm Hz1/2 W−1 which correspondsto the highest value reported for an AlGaN-based Schottkyphotodiodes. Differential resistance at zero bias isR0=1.31016 . According to the responsivity measure-ments, the photocurrent does not significantly increase after20 V. Therefore, we set the unity gain at 20 V. From thephotocurrent and dark current data, we calculated the ava-lanche gain by first taking the difference between the multi-plied photocurrent and dark current data, and then normaliz-ing it with respect to the unmultiplied difference of thephotocurrent and dark current. The avalanche gain at a 68 Vreverse bias was 1560, which is the highest reproducible ava-lanche gain reported in the literature for AlGaN-based solar-blind APDs. We proved reproducibility by way of taking thedark current measurement after several photocurrent mea-surements, in which we saw no significant change in darkFIG. 1. Dark current measurement data from a 40 m diameter photodetec-tor device.FIG. 2. a Transmission data from a double side polished wafer which isused in the fabrication. b Responsivity measurements result from a150 m diameter device.FIG. 3. a Gain measurements for a 40 m diameter device. b Avalanchegain extracted from the photocurrent measurements.163506-2 Tut et al. Appl. Phys. Lett. 90, 163506 2007current ten scans, and consequently, also none in the ava-lanche gain results ten scans, which is shown in Fig. 3.We determined the voltage at which the unity gain oc-curs via C-V and lock-in assisted responsivity measurements.After the 20 V bias, the capacitance does not change whichis an indicator of full depletion of the junction. Close to 20 Vthe lock-in assisted responsivity does not change consider-ably and after 20 V it does not increase steadily and signifi-cantly unlike avalanche gain which starts generally after60 V.We also measured the dark currents under different tem-peratures. In Fig. 4, the dark current of a photodetectorshows a strong dependence on temperature. This resultproves that Zener tunneling, which is a temperature insensi-tive process, is not a possible gain mechanism in these de-vices. The gain measurements showed an exponential depen-dence on voltage, in which we infer from this result that thephotoconductive gain is not a possible gain mechanism inour devices. We know that the photoconductive gain in-creases linearly with voltage.19,22 Therefore, we concludethat the gain in these devices result from the avalanche mul-tiplication of the photogenerated carriers in the active regionof the devices.In summary, we present the MOCVD growth, fabrica-tion, and characterization of AlGaN-based solar-blind APDs.The avalanche gain at 68 V was in excess of 1560 with noGeiger mode breakdown. The electric field was on the orderof 1.88 MV/cm. The gain in the active region of the devicesis attributed to the avalanche multiplication of the photoge-nerated carriers. This work demonstrates the high potentialof AlGaN APDs for replacement of the PMTs for high sen-sitive solar-blind photodetector applications.This work is supported by the European Union under theprojects EU-NoE-METAMORPHOSE, EU-NoE-PHOREMOST, and TUBITAK under Projects Nos.104E090, 105E066, 105A005, and 106A017. One of the au-thors E.O. also acknowledges partial support from theTurkish Academy of Sciences.1E. Ozbay, N. Biyikli, I. Kimukin, T. Tut, T. Kartaloglu, and O. Aytur,IEEE J. Sel. Top. Quantum Electron. 10, 742 2004.2C. J. Collins, U. Chowdhury, M. M. Wong, B. Yang, A. L. Beck, and R. D.Dupuis, Electron. Lett. 38, 824 2002.3N. Biyikli, T. Kartaloglu, O. Aytur, I. Kimukin, and E. Ozbay, Appl. Phys.Lett. 79, 2838 2001.4N. Biyikli, I. Kimukin, T. Tut, O. Aytur, and E. Ozbay, Appl. Phys. Lett.81, 3272 2002.5S. Butun, M. Gokkavas, HongBo Yu, and E. Ozbay, Appl. Phys. Lett. 89,073503 2006.6J. C. Campbell, S. Demiguel, F. Ma, A. Beck, X. Guo, S. Wang, X. Zheng,X. Li, J. D. Beck, M. A. Kinch, A. Huntington, L. A. Coldren, J. Decobert,and N. Tscherptner, IEEE J. Quantum Electron. 10, 777 2004.7T. Tut, S. Butun, B. Butun, M. Gokkavas, H. B. Yu, and E. Ozbay,Appl. Phys. Lett. 87, 223502 2005.8N. Biyikli, I. Kimukin, T. Kartaloglu, O. Aytur, and Ekmel Ozbay,Phys. Status Solidi C 7, 2314 2003.9Y. Wang, K. Brennan, and P. Ruden, IEEE J. Quantum Electron. 27, 2321991.10P. Ruden and S. Krishnankutty, IEEE Trans. Electron Devices 46, 23481999.11C. Sevik and C. Bulutay, Appl. Phys. Lett. 83, 1382 2003.12K. A. McIntosh, R. J. Molnar, L. J. Mahoney, A. Lightfoot, M. W. Geis,K. M. Molvar, I. Melngailis, R. L. Aggarwal, W. D. Goodhue, S. S. Choi,D. L. Spears, and S. Verghese, Appl. Phys. Lett. 75, 3485 1999.13J. C. Carrano, D. J. H. Lambert, C. J. Eiting, C. J. Collins, T. Li, S. Wang,B. Yang, A. L. Beck, R. D. Dupuis, and J. C. Campbell, Appl. Phys. Lett.76, 924 2000.14A. Osinsky, M. S. Shur, R. Gaska, and Q. Chen, Electron. Lett. 34, 6911998.15S. Verghese, K. A. McIntosh, R. J. Molnar, L. J. Mahoney, R. L.Aggarwal, M. W. Geis, K. M. Molvar, E. K. Duerr, and I. Melngailis,IEEE Electron Device Lett. 48, 502 2001.16K. A. McIntosh, R. J. Molnar, L. J. Mahoney, K. M. Molvar, N. Efremov,and S. Verghese, Appl. Phys. Lett. 76, 3938 2000.17B. Yang, T. Li, K. Heng, C. Collins, S. Wang, J. C. Carrano, R. D. Dupuis,J. C. Campbell, M. J. Schurman, and I. T. Ferguson, IEEE J. QuantumElectron. 36, 1389 2000.18J. B. Limb, D. Yoo, J. H. Ryou, W. Lee, S. C. Shen, R. D. Dupuis, M. L.Reed, C. J. Collins, M. Wraback, D. Hanser, E. Preble, N. M. Williams,and K. Evans, Appl. Phys. Lett. 89, 011112 2006.19R. McClintock, A. Yasan, K. Minder, P. Kung, and M. Razeghi,Appl. Phys. Lett. 87, 241123 2005.20T. Tut, M. Gokkavas, B. Butun, S. Butun, E. Ulker, and E. Ozbay,Appl. Phys. Lett. 89, 183524 2006.21T. Tut, N. Biyikli, I. Kimukin, T. Kartaloglu, O. Aytur, S. Unlu, and E.Ozbay, Solid-State Electron. 49, 117 2005.22S. M. Sze, Physics of Semiconductor Devices, 2nd ed. Wiley, New York,1981, Chap. 13, p. 744.FIG. 4. Dark current measurement data with varying temperatures.163506-3 Tut et al. Appl. Phys. Lett. 90, 163506 2007

http://repository.bilkent.edu.tr/bitstream/11693/23482/1/AlxGa1-xN-based_avalanche_photodiodes_with_high_reproducible_avalanche_gain.pdf

AlxGa1-xN-based avalanche photodiodes with high reproducible avalanche gain

Abstract

Similar works

Full text

Available Versions

Bilkent University Institutional Repository

Bilkent University Institutional Repository