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Page 2. Outline. Background reviewSimulation Device fabricationExperimental resultsConclusionsAcknowledgements. Page 3. Advantages of ZnO as Light Emitting Material . Unique properties of ZnO Wurtzite (Hexagonal) structure II-VI compound semiconductor Zn and O at 4f-site Direct wide bandgap = 3.37eV Transparent conducting oxide Binding energy of exciton (300K)= 60 meV.

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    1. Page 1 Good morning, everyone. I’m Hungta Wang. My talk is “band edge electroluminescence from N+-implanted bulk ZnO.Good morning, everyone. I’m Hungta Wang. My talk is “band edge electroluminescence from N+-implanted bulk ZnO.

    2. Page 2 Here is the outline of my talk. First of all, it’s background review and simulation. Following is device fabrication and experimental results. Finally, it’s conclusions and acknowledgements. Here is the outline of my talk. First of all, it’s background review and simulation. Following is device fabrication and experimental results. Finally, it’s conclusions and acknowledgements.

    3. Page 3 Advantages of ZnO as Light Emitting Material ZnO is a very popular material suitable for applications in UV light emitters, UV detectors, high power electronics, and chemical or gas sensors. The reason is that ZnO has unique Material properties. It has Wurzite structure. It’s a II-VI compound semiconductor. Zn and O are at 4f sites. The direct bandgap is 3.37eV. It’s a transparent conducting oxide having the exciton binding energy at 300K, 60meV. Especially, ZnO is a potential candidate material to replace GaN for LED application because it has higher exciton binding energy. Also, the high quality bulk substrate is already commercially available; Beside, ZnO has easier wet etching and cheaper growth technology. However, as we know, ZnO LED is still unavailable due to a lack of high quality p-type films.ZnO is a very popular material suitable for applications in UV light emitters, UV detectors, high power electronics, and chemical or gas sensors. The reason is that ZnO has unique Material properties. It has Wurzite structure. It’s a II-VI compound semiconductor. Zn and O are at 4f sites. The direct bandgap is 3.37eV. It’s a transparent conducting oxide having the exciton binding energy at 300K, 60meV. Especially, ZnO is a potential candidate material to replace GaN for LED application because it has higher exciton binding energy. Also, the high quality bulk substrate is already commercially available; Beside, ZnO has easier wet etching and cheaper growth technology. However, as we know, ZnO LED is still unavailable due to a lack of high quality p-type films.

    4. Page 4 p-i-n LED Using Temperature Modulated Epitaxy [A. Tsukazaki et al.] Reviewing the literature in the recent years, several research groups have made lots of great progress toward ZnO LED. This p-i-n LED was done by Dr. Kawasaki’s group. The p type film is made by repeated temperature modulation epitaxy, using nitrogen as acceptor. The device turn-on is 7V. The EL shows a near-band-edge spectrum. Reviewing the literature in the recent years, several research groups have made lots of great progress toward ZnO LED. This p-i-n LED was done by Dr. Kawasaki’s group. The p type film is made by repeated temperature modulation epitaxy, using nitrogen as acceptor. The device turn-on is 7V. The EL shows a near-band-edge spectrum.

    5. Page 5 p-n LED Using MOCVD [W. Z. Xu et al.] Dr. Ye’s group also achieved this p-n junction LED by MOCVD using nitrogen as acceptor. Today, he will also give us a nice talk. Dr. Ye’s group also achieved this p-n junction LED by MOCVD using nitrogen as acceptor. Today, he will also give us a nice talk.

    6. Page 6 p-n LED Using Sputtering [Jae-Hong Lim et al.] This is another remarkable p-n LED achieved by Dr. Park’s group using sputtering technique. They use phosphorus as accepter for p-type ZnO. The turn-on voltage is 3.2 V with EL emission peak at 380nm. This is another remarkable p-n LED achieved by Dr. Park’s group using sputtering technique. They use phosphorus as accepter for p-type ZnO. The turn-on voltage is 3.2 V with EL emission peak at 380nm.

    7. Page 7 MIS diode Using Ion implantation [Ya. I. Alivov et al.] Excepted to temperature modulated epitaxy, MOCVD, and sputtering, ion implantation is also used to realize p-type ZnO. Several research groups have made p-type ZnO by ion implantation, but, however, a p-n LED have not been made. This is a MIS diode made by Dr. Pustovit group using N ion implanted ZnO thin film. The turn-on is 3V with a band-edge EL. Excepted to temperature modulated epitaxy, MOCVD, and sputtering, ion implantation is also used to realize p-type ZnO. Several research groups have made p-type ZnO by ion implantation, but, however, a p-n LED have not been made. This is a MIS diode made by Dr. Pustovit group using N ion implanted ZnO thin film. The turn-on is 3V with a band-edge EL.

    8. Page 8 ZnO LED by Ion Implantation So, the reasons we interest in this study is that: Ion implantation is a well-developed technology, it’s a high yield rate and low cast technology; Besides, ZnO p-type film by ion implantation is already made by several groups. Moreover, applying ion implantation to bulk ZnO will dramatically decrease the fabrication process and costs. However, it’s not a easy job because it’s more difficult to activate implanted doapnt in damaged ZnO. So, the reasons we interest in this study is that: Ion implantation is a well-developed technology, it’s a high yield rate and low cast technology; Besides, ZnO p-type film by ion implantation is already made by several groups. Moreover, applying ion implantation to bulk ZnO will dramatically decrease the fabrication process and costs. However, it’s not a easy job because it’s more difficult to activate implanted doapnt in damaged ZnO.

    9. Page 9 Depth Profile Modeling Here, we use a very easy simulator, called profile code, to study the implantation distribution. Choosing specific ion energy and dose, a nice doping distribution can easily obtained. This is a model of N+ ion implantation to ZnO substrates. In order to get a uniform concentration of 1019 with a depth of 300nm, four dose are used. The ion energy ranges from 10 to 140keV, the dose ranges from 1013 to 1014cm-2. 7 degree is also applied to avoid channel effect.Here, we use a very easy simulator, called profile code, to study the implantation distribution. Choosing specific ion energy and dose, a nice doping distribution can easily obtained. This is a model of N+ ion implantation to ZnO substrates. In order to get a uniform concentration of 1019 with a depth of 300nm, four dose are used. The ion energy ranges from 10 to 140keV, the dose ranges from 1013 to 1014cm-2. 7 degree is also applied to avoid channel effect.

    10. Page 10 Collision Event Modeling In order to understand the damages induced by ion implantation, we used a popular simulator, called SRIM-2003, to model the defect distribution. This is a collision event modeling of the 1st dose, 2.4x1014cm-2 with 140keV, At 2000A, the ratio of Zn vacancy, oxygen vacancy, and replacement is about 12:7:1. The vacancy is about 20 times of the replacement.In order to understand the damages induced by ion implantation, we used a popular simulator, called SRIM-2003, to model the defect distribution. This is a collision event modeling of the 1st dose, 2.4x1014cm-2 with 140keV, At 2000A, the ratio of Zn vacancy, oxygen vacancy, and replacement is about 12:7:1. The vacancy is about 20 times of the replacement.

    11. Page 11 Device Fabrication This picture is a device wire-bonded for EL test. The size is 2 by 4 mm. These circles are the contact metal for implanted ZnO. Rectangular gray area is the back contact metal for ZnO substrate. We use a commercialized ZnO substrate from Cermet. It’s undoped, I grade with electron concentration of 1017, the mobility is ~190cm2/V.s. This company also achieved pn LED in 2005. Dr. Pan will give us a nice talk today, too! The substrate was implanted by the four doses, following by thermal activation using either RTA or furnace. The annealing temperature is from 600C to 1000C. After N activation, the back contact metal is Ti/Au and the front contact metal is Ni/Au using e-beam evaporation. This picture is a device wire-bonded for EL test. The size is 2 by 4 mm. These circles are the contact metal for implanted ZnO. Rectangular gray area is the back contact metal for ZnO substrate. We use a commercialized ZnO substrate from Cermet. It’s undoped, I grade with electron concentration of 1017, the mobility is ~190cm2/V.s. This company also achieved pn LED in 2005. Dr. Pan will give us a nice talk today, too! The substrate was implanted by the four doses, following by thermal activation using either RTA or furnace. The annealing temperature is from 600C to 1000C. After N activation, the back contact metal is Ti/Au and the front contact metal is Ni/Au using e-beam evaporation.

    12. Page 12 I-V of Metal Contacts

    13. Page 13 Diode I-V Characteristics

    14. Page 14 Light Intensity Performance

    15. Page 15 Electroluminescence at Room Temp.

    16. Page 16 Electroluminescence at 120K

    17. Page 17 Conclusions MIS diode was achieved by N+_implanted ZnO bulk. Yellow EL was obtained from N+-implanted ZnO at room T. Band-edge EL was obtained at 120K. Future work: 1. p-type conductivity. 2. pn LED.

    18. Page 18 Acknowledgements This work at UF is supported by: DOE Grant No. DE-FC26-04NT42271. DOE Contract No. DE-AC05-00OR22725. USAFOSR under Grant No. F49620-03-1-0370. Thank you very much!

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