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ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes.

DE2008923721

Publication Date	2007
Personal Author	Ren, F.; Norton, D. P.; Pearton, S.
Page Count	87
Abstract	By 2015, the US Department of Energy has set as a goal the development of advanced solid state lighting technologies that are more energy efficient, longer lasting, and more cost-effective than current technology. One approach that is most attractive is to utilize light-emitting diode technologies. Although III-V compound semiconductors have been the primary focus in pursuing this objective, ZnO-based materials present some distinct advantages that could yield success in meeting this objective. As with the nitrides, ZnO is a direct bandgap semiconductor whose gap energy (3.2 eV) can be tuned from 3.0 to 4 eV with substitution of Mg for higher bandgap, Cd for lower bandgap. ZnO has an exciton binding energy of 60 meV, which is larger than that for the nitrides, indicating that it should be a superior light emitting semiconductor. Furthermore, ZnO thin films can be deposited at temperatures on the order of 400-600 C, which is significantly lower than that for the nitrides and should lead to lower manufacturing costs. It has also been demonstrated that functional ZnO electronic devices can be fabricated on inexpensive substrates, such as glass. Therefore, for the large-area photonic application of solid state lighting, ZnO holds unique potential. A significant impediment to exploiting ZnO in light-emitting applications has been the absence of effective p-type carrier doping. However, the recent realization of acceptor-doped ZnO material overcomes this impediment, opening the door to ZnO light emitting diode development In this project, the synthesis and properties of ZnO-based pn junctions for light emitting diodes was investigated. The focus was on three issues most pertinent to realizing a ZnO-based solid state lighting technology, namely (1) achieving high p-type carrier concentrations in epitaxial and polycrystalline films, (2) realizing band edge emission from pn homojunctions, and (3) investigating pn heterojunction constructs that should yield efficient light emission. The project engaged established expertise at the University of Florida in ZnO film growth (D. Norton), device fabrication (F. Ren) and wide bandgap photonics (S. Pearton). It addressed p-type doping and junction formation in (Zn,Mg)O alloy thin films. The project employed pulsed laser deposition for film growth. The p-type dopant of interest was primarily phosphorus, given the recent results in our laboratory and elsewhere that this anions can yield p-type ZnO-based materials. The role of Zn interstitials, oxygen vacancies, and/or hydrogen complexes in forming compensating shallow donor levels imposes the need to simultaneously consider the role of in situ and post-growth processing conditions.
Keywords	Thin films Light emitting diodes Lifetime Electroluminescence Alloys Anions Binding Excitons Fabrication Heterojunctions Homojunctions Photoluminescence Substrates X-ray diffraction
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Florida Univ., Gainesville.; Florida Univ., Gainesville. Dept. of Materials Science and Engineering.; Florida Univ., Gainesville. Dept. of Chemical Engineering.; Department of Energy, Washington, DC.; National Energy Technology Lab., Morgantown, WV.
Supplemental Notes	Prepared in cooperation with Florida Univ., Gainesville. Dept. of Materials Science and Engineering., Florida Univ., Gainesville. Dept. of Chemical Engineering. and National Energy Technology Lab., Morgantown, WV. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200820
Contract Number	FC26-04NT42271

ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes.

ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes.
DE2008923721

Publication Date	2007
Personal Author	Ren, F.; Norton, D. P.; Pearton, S.
Page Count	87
Abstract	By 2015, the US Department of Energy has set as a goal the development of advanced solid state lighting technologies that are more energy efficient, longer lasting, and more cost-effective than current technology. One approach that is most attractive is to utilize light-emitting diode technologies. Although III-V compound semiconductors have been the primary focus in pursuing this objective, ZnO-based materials present some distinct advantages that could yield success in meeting this objective. As with the nitrides, ZnO is a direct bandgap semiconductor whose gap energy (3.2 eV) can be tuned from 3.0 to 4 eV with substitution of Mg for higher bandgap, Cd for lower bandgap. ZnO has an exciton binding energy of 60 meV, which is larger than that for the nitrides, indicating that it should be a superior light emitting semiconductor. Furthermore, ZnO thin films can be deposited at temperatures on the order of 400-600 C, which is significantly lower than that for the nitrides and should lead to lower manufacturing costs. It has also been demonstrated that functional ZnO electronic devices can be fabricated on inexpensive substrates, such as glass. Therefore, for the large-area photonic application of solid state lighting, ZnO holds unique potential. A significant impediment to exploiting ZnO in light-emitting applications has been the absence of effective p-type carrier doping. However, the recent realization of acceptor-doped ZnO material overcomes this impediment, opening the door to ZnO light emitting diode development In this project, the synthesis and properties of ZnO-based pn junctions for light emitting diodes was investigated. The focus was on three issues most pertinent to realizing a ZnO-based solid state lighting technology, namely (1) achieving high p-type carrier concentrations in epitaxial and polycrystalline films, (2) realizing band edge emission from pn homojunctions, and (3) investigating pn heterojunction constructs that should yield efficient light emission. The project engaged established expertise at the University of Florida in ZnO film growth (D. Norton), device fabrication (F. Ren) and wide bandgap photonics (S. Pearton). It addressed p-type doping and junction formation in (Zn,Mg)O alloy thin films. The project employed pulsed laser deposition for film growth. The p-type dopant of interest was primarily phosphorus, given the recent results in our laboratory and elsewhere that this anions can yield p-type ZnO-based materials. The role of Zn interstitials, oxygen vacancies, and/or hydrogen complexes in forming compensating shallow donor levels imposes the need to simultaneously consider the role of in situ and post-growth processing conditions.
Keywords	Thin films Light emitting diodes Lifetime Electroluminescence Alloys Anions Binding Excitons Fabrication Heterojunctions Homojunctions Photoluminescence Substrates X-ray diffraction
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Florida Univ., Gainesville.; Florida Univ., Gainesville. Dept. of Materials Science and Engineering.; Florida Univ., Gainesville. Dept. of Chemical Engineering.; Department of Energy, Washington, DC.; National Energy Technology Lab., Morgantown, WV.
Supplemental Notes	Prepared in cooperation with Florida Univ., Gainesville. Dept. of Materials Science and Engineering., Florida Univ., Gainesville. Dept. of Chemical Engineering. and National Energy Technology Lab., Morgantown, WV. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200820
Contract Number	FC26-04NT42271