1. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes Prime Recipient: University of Florida Work Performed Under Agreement: DE-FC26-04NT42271 U. S. Department of Energy National Energy Technology Laboratory COR: Ryan Egidi David P. Norton, P.I. Materials Science and Engr. University of Florida Stephen Pearton Materials Science and Engr. University of Florida Fan Ren Chemical Engr. University of Florida

2. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Project Objectives Develop solid state lighting technology based on wide bandgap ZnO light emitting diodes (LED) –Achieve high p-type carrier concentrations in epitaxial (Zn,Mg)O thin films –Realize band edge emission from a ZnO-based pn homojunction –Achieve band edge emission for ZnO-based pn heterojunctions that are designed to yield efficient light emission. –Related objectives Understand the doping behavior of phosphors and nitrogen in ZnO and ZnMgO Identify the potential and limitations of ZnO pn junction LED performance Achieve electroluminescence in polycrystalline ZnO-based pn junctions fabricated on glass. c a substrate n + -ZnO n-ZnMgO ZnO p-ZnMgO p-ZnO Ohmic ring ħωħω n-ZnMgOp-ZnMgO ZnO

3. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Expected Benefits Enhanced Performance in LEDs –Light-emitting diode technologies are the most attractive approach to energy-efficient solid state lighting –ZnO appears equivalent to the nitrides ( leading material candidate) for all relevant optical properties and has an exciton state that is significantly more stable at room temperature holds significant potential to outperform the nitride devices Reduction in Cost –ZnO-based devices have been realized using thin films deposited at temperatures on the order of 400-600˚C, which is significantly lower that that for the nitrides. Reduced temperature alone should lead to lower manufacturing costs. –Functional ZnO electronic devices can be fabricated on inexpensive substrates, such as glass. For the large-area photonic application of solid state lighting, polycrystalline ZnO LED’s would present a remarkable opportunity for technology. ZnO GaN ZnO Bandgap (eV) 3.44 3.2 µ e (cm 2 /V-sec) 220 200 µ h (cm 2 /V-sec) 10 5-50 m e 0.27m o 0.24m o m h 0.8m o 0.59m o exciton binding 28 60!! energy (meV)

4. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Budget Period Project Funding Profile BP#1BP#2BP#3Total Gov. Funding Cost Share Gov. Funding Cost Share Gov. Funding Cost Share Gov. Funding Cost Share Recipient$315,167$78,792$302,128$75,532$297,242$74,310$914,537$228,634 CS %:20% BP#3 – Oct. 2006 – Sept. 2007 (estimated) October24,000 November24,000 December24,000 January24,000 February24,000 March24,000 April24,000 May24,000 June24,000 July24,000 August27,000 September30,242 total297,242 BP#2– Oct. 2005 – Oct. 2006 (estimated) October27,128 November25,000 December25,000 January25,000 February25,000 March25,000 April25,000 May25,000 June25,000 July25,000 August25,000 September25,000 total 302,128 Total costs 10/01/05-9/30/05 $302,128 Total costs 10/01/06-9/30/07 $297,242

5. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ZnO-based pn junctions for light emitting diodes Three pertinent issues –Achieve high p-type carrier concentrations in epitaxial and polycrystalline films Materials issue SUBSTRATE n-type ZnO p-type ZnO contact Glass substrate n + -ZnO n-ZnMgO ZnO p-ZnMgO p-ZnO Ohmic ring ħωħω n-ZnMgOp-ZnMgO ZnO –Realizing band edge emission from pn homojunctions Proof of concept –Investigating pn heterojunction constructs that should yield efficient light emission. Device Development Project Status (Budget Period 2)

6. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Project Status (Budget Period 2) Research task with milestones in Budget Period 2 TitleMetric/Method of VerificationProjected date for milestone completion (month/year) Growth of p-type (Zn,Mg)O filmsAchieve 10E17 cm-3 p-type carrier density in ZnO film7/06 Formation of pn homojunction thin film structure Optimize crystalline/polycrystalline pn junction structure film growth process with respect to IV 1/06 Fabrication of pn homojunction deviceAchieve UV light emission from pn homojunction device4/06 Characterization of pn homojunctionDetermine efficacy of pn homojunction for LED7/06 Growth of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterostructure Optimization of epitaxial heterostructure thin film junction7/06 Fabrication of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterojunction devices Achieve nonlinear rectifying IV in pn heterojunction device7/06

7. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Sapphire Undoped buffer ZnO :P 0.005 Reproducibility of p-type ZnO growth RTA annealing study 400 ℃ 800 ℃ ① Buffer : 20 mTorr for 1 hour ② Post-annealing for 1 hour (150mTorr) ③ ZnO:P growth for 3 hours - Structure A) Temperature effects (Fixed pressure : 150mTorr) B) Pressure effects (Fixed temperature 700 ℃ ) Research task: Achieve 10 17 cm -3 p-type carrier density in ZnO film

8. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 (ZnO:P 0.005 ) - Hall data (150 mTorr growth pressure) Growth Temp ( ℃ ) As grown RTA temperature ( ℃ ) / time (min) 850900950 2 min3 min2 min3 min1 min2 min3 min 600 4400 Ω-cm 3.9E+16cm -3 0.037cm 2 /Vs 4400 Ω-cm 2.3E+15cm -3 0.63cm 2 /Vs 140 Ω-cm 1.2E+17cm -3 0.37cm 2 /Vs 9.0 Ω-cm 1.8E+18cm -3 0.38cm 2 /Vs 1.1 Ω-cm 4.9E+18cm -3 1.2cm 2 /Vs 0.76 Ω-cm 5.4E+18cm -3 1.5cm 2 /Vs 650 1700 Ω-cm 2.9E+15cm -3 1.3cm 2 /Vs 490 Ω-cm 1.2E+16cm -3 1.0cm 2 /Vs 70 Ω-cm 4.3E+17cm -3 0.20cm 2 /Vs 5.0 Ω-cm 3.0E+18cm -3 0.41cm 2 /Vs 6.3 Ω-cm 2.7E+18cm -3 0.36cm 2 /Vs 11 Ω-cm 2.0E+19cm -3 0.028cm 2 /Vs 700 480 Ω-cm 1.4E+16cm -3 0.98cm 2 /Vs 3400 Ω-cm 3.9E+15cm -3 0.47cm 2 /Vs 1700 Ω-cm 8.8E+15cm -3 0.40cm 2 /Vs 360 Ω-cm 4.2E+16cm -3 0.40cm 2 /Vs 24Ω-cm 4.6E+17cm -3 0.56cm 2 /Vs 17 Ω-cm 5E+17cm -3 0.71cm 2 /Vs 19 Ω-cm 4.1E+17cm -3 0.80cm 2 /Vs 39 Ω-cm 2.4E+17cm -3 0.66cm 2 /Vs 750 2.2 Ω-cm 4.8E+17cm -3 5.8cm 2 /Vs 630 Ω-cm 1.4E+16cm -3 0.68cm 2 /Vs 900 Ω-cm 1.0E+16cm -3 0.67cm 2 /Vs 140 Ω-cm 2.2E+17cm -3 0.21cm 2 /Vs 4.8 Ω-cm 1.1E+18cm -3 1.1cm 2 /Vs 7.1 Ω-cm 4E+17cm -3 2.4cm 2 /Vs 21 Ω-cm 9.5E+17cm -3 0.30cm 2 /Vs 65 Ω-cm 1.0E+18cm -3 0.094cm 2 /Vs 800 2.0 Ω-cm 4.5E+17cm -3 7.1cm 2 /Vs 360 Ω-cm 2.6E+16cm -3 0.66cm 2 /Vs 1400 Ω-cm 5.1cm -3 0.91cm 2 /Vs 100 Ω-cm 2.6E+16cm -3 2.4cm 2 /Vs 4.9 Ω-cm 3.6E+18cm -3 0.36cm 2 /Vs 17 Ω-cm 2E+18cm -3 0.15cm 2 /Vs 4.5 Ω-cm 3.7E+18cm -3 0.38cm 2 /Vs 15 Ω-cm 2.0E+17cm -3 2.2cm 2 /Vs : p or n-type: p-type : n-type

9. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ( ZnO:P 0.005 ) – Hall data (700°C growth temperature) P(O 2 ) (m Torr) As grown RTA temperature ( ℃ ) / time (min) 850900950 2 min3 min1 min2 min3 min1 min2 min3 min 150 480 Ω-cm 1E+16cm -3 0.98cm 2 /Vs 3400 4E+15cm -3 0.47cm 2 /Vs 1700 Ω-cm 9E+15cm -3 0.40cm 2 /Vs 360 Ω-cm 4E+16cm -3 0.40cm 2 /Vs 24 Ω-cm 4E+17cm -3 0.56cm 2 /Vs 17 Ω-cm 5E+17cm -3 0.71cm 2 /Vs 19 Ω-cm 4E+17cm -3 0.90cm 2 /Vs 39 Ω-cm 2E+17cm -3 0.68cm 2 /Vs 100 5.5 Ω-cm 2E+19cm -3 0.07cm 2 /Vs - 9400Ω-cm 6E+13cm -3 10cm 2 /Vs 20 Ω-cm 7E+17cm -3 0.44cm 2 /Vs 76 Ω-cm 2E+17cm -3 0.39cm 2 /Vs 34 Ω-cm 1E+18cm -3 0.14cm 2 /Vs 33 Ω-cm 4E+16cm -3 5.3cm 2 /Vs 38 Ω-cm 1E+18cm -3 0.11cm 2 /Vs 36 Ω-cm 2E+18cm -3 0.08cm 2 /Vs 50 1.1 Ω-cm 8E+18cm -3 0.65cm 2 /Vs 8E+4Ω-cm 5E+13cm -3 1.6cm 2 /Vs 4E+4Ω-cm 4E+13cm -3 4.3cm 2 /Vs 170 Ω-cm 1E+16cm -3 3.4cm 2 /Vs 280 Ω-cm 9E+16cm -3 0.24cm 2 /Vs 4.7E6Ω-cm 1E+12cm -3 1.1cm 2 /Vs 33 Ω-cm 2E+17cm -3 0.94cm 2 /Vs 8.4 Ω-cm 4E+18cm -3 0.20cm 2 /Vs 28 Ω-cm 4E+19cm -3 0.005cm 2 /Vs 10 1.4 Ω-cm 4E+18cm -3 1.3cm 2 /Vs 9400 Ω-cm 4E+16cm -3 0.02cm 2 /Vs 3100 Ω-cm 5E+15cm -3 0.44cm 2 /Vs 27 Ω-cm 9E+16cm -3 2.6cm 2 /Vs 5700 Ω-cm 4E+16cm -3 0.03cm 2 /Vs 51 Ω-cm 9E+18cm -3 0.01cm 2 /Vs 45 Ω-cm 6E+16cm -3 2.5cm 2 /Vs 25 Ω-cm 1E+19cm -3 0.02cm 2 /Vs 58 Ω-cm 3E+18cm -3 0.04cm 2 /Vs 1 0.75 Ω-cm 9E+18cm -3 0.90cm 2 /Vs 1000Ω-cm 2E+17cm -3 0.03cm 2 /Vs 840 Ω-cm 4E+17cm -3 0.02cm 2 /Vs 3.3 Ω-cm 3E+18cm -3 0.61cm 2 /Vs 7.6 Ω-cm 3E+18cm -3 0.28cm 2 /Vs 220 Ω-cm 9E+16cm -3 0.33cm 2 /Vs 2.3 Ω-cm 3E+18cm -3 0.89cm 2 /Vs 2.9 Ω-cm 5E+18cm -3 0.43cm 2 /Vs 4.6 Ω-cm 4E+18cm -3 0.33cm 2 /Vs : p or n-type: p-type : n-type

10. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 2. Zn 0.95 Mg 0.05 O:P 0.02 (Hall data) Growth Temperature ( ℃ ) As grown RTA temperature ( ℃ ) 600700800900 550 (ZMP-13) 4.98E+16 (M) 0.14546 (R) 860.87 2.70E+17 (M) 0.085742 (R) 269.23 3.67E+16 (M) 0.25074 (R) 678.83 5.20E+14 (M) 1.2396 (R) 9591.4 1.03E+17 (M) 0.14526 (R) 419.61 600 (ZMP-14) 7.18E+16 (M) 1.4197 (R) 61.309 1.54E+17 (M) 0.37251 (R) 108.86 7.06E+16 (M) 0.37137 (R) 238.78 1.59E+16 (M) 0.40281 (R) 962.38 2.89E+17 (M) 0.58556 (R) 36.798 650 (ZMP-15) 4.92E+13 (M) 0.12126 (R) 1.09E+6 9.34E+17 (M) 0.5125 (R) 12903 4.50E+13 (M) 2.3158 (R) 60500 9.44E+13 (M) 0.82754 (R) 78126 6.16E+17 (M) 0.52519 (R) 19.321 650 (ZMP-16) 3.49E+18 (M) 34.55 (R) 0.051714 3.90E+18 (M) 34.913 (R) 0.045842 3.45E+18 (M) 33.670 (R) 0.053734 2.53E+17 (M) 3.0596 (R) 8.0610 1.38E+17 (M) 5.33 (R) 8.47 p=10 16 cm -3

11. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 1. Zn 0.9 Mg 0.1 O:P 0.02 (Hall) RTA temperature As grown600700800850900925975 Thickness of buffer layer (nm) 30 ( ZMP-1 ) 3.6735E14 (M) 0.5361 (R) 32457 2.5582E+15 0.7151 3394.2 1.6799E+16 0.40346 925.05 6.3720E+14 0.60931 16061 100 ( ZMP-2 ) 2.6561E14 (M) 0.4735 (R)49655 2.1134E+15 0.25347 11652 2.8783E+15 0.34103 6357.1 4.1998E+14 0.26480 57642 200 ( ZMP-3 ) 2.8614E15 (M) 0.1893 (R) 11516 2.7098E+14 0.45735 50565 1.0210E+14 0.50579 12131 Semi-insulating 4.27E+14 (M) 18.25 (R) 788 400 ( ZMP-4 ) 7.4256E17 (M) 4.5337 (R) 1.855 1.0167E+15 0.93540 6551.3 2.9490e+14 1.0129 20883 Semi-insulating 1.29E+17 0.0549 875.03 Growth Temperature 550 ℃ ( ZMP-10 ) 6.8235E+15 (M) 1.2349 (R) 732.49 4.56E+16 (M) 0.11955 (R) 1140.1 7.72E+16 (M) 0.1129 (R) 720.15 6.36E+16 (M) 2.6358 (R) 37.15 6.31E+17 (M) 7.9413 (R) 1.2466 600 ℃ ( ZMP-5 ) 7.784E+17 (M) 0.1382 (R) 57.388 1.7995E+15 0.42028 8214.4 3.5071E+14 0.49244 36207 Semi-insulating (875 ℃ ) 600 ℃ ( ZMP-11 ) 1.1999E+13 (M) 56.677 (R) 8932.8 5.58E+15 (M) 0.12621 (R) 8909.4 8.24E+14 (M) 0.21207 (R) 35716 1.0427E+12 (M) 139.02 (R) 46452 4.35E+17 (M) 1.4595 (R) 9.8393 650 ℃ ( ZMP-12 ) 4.2397E+16 (M) 0.39604 (R) 371.64 6.95E+16 (M) 0.07554 (R) 1198.4 1.64E+17 (M) 0.058 (R) 657 1.68E+16 (M) 0.24019 (R) 1564.7 4.28E+17 (M) 1.9607 (R) 7.4443 700 ℃ (ZMP-6) 1.499E+17 (M) 1.1119 (R) 37.421 7.115E+16 0.411 212.46 4.21E+16 0.2797 531.03 1.095E+15 1.1135 5094.7 6.4643E+16 0.52519 183.36 800 ℃ (ZMP-7) 4.67E+18 (M) 39.436 (R) 0.033875 3.36E+18 40.78 0.0455 3.44E+15 11.748 156.65 2.824E+14 100.66 218.98 6.7577E+16 1.3676 67.410 900 ℃ (ZMP-8) 1.368E+19 (M) 33.410 (R) 0.013655 1.4026E+19 27.567 0.016144 1.4829E+19 2.3144 0.18208 7.0575E+17 0.90632 9.7647 3.8507E+17 1.8439 8.7689 p=1-6x10 15 cm -3

12. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Narrow Omega Rocking Curve ◈ Hall data n = 2.4E+16 ( /cm 3 ) µ = 87.7 ( cm 2 /Vs ) ρ = 3.1 ( ohmcm ) High-quality undoped ZnO epitaxial films realized by PLD ◈ Growth conditions Sapphire Substrate Buffer layer (25nm) Undoped ZnO ( ~ 1um) ▶ Bulk layer growth - Target : undoped ZnO - T g : 650 ℃ - Pressure : 10 mTorr ( O 2 + O 3 mixture gas ) - Laser : 180 mJ / 4 Hz - Ablation time : 2 hrs 20 min ( 1.22 Å / s ) ▶ Buffer layer growth - Target : undoped ZnO - Pressure : 1m Torr ( O 2 + O 3 mixture gas ) - T g : 850 ℃ - Laser : 180 mJ / 1 Hz - Ablation time : 9 min ( 0.53 Å / s ) ( rms : 1.557 nm)

13. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 p-n homojunctions in n-ZnO bulk single crystals by diffusion from a Zn 3 P 2 source p-n junctions have been formed in lightly n-type (10 17 cm -3 ) bulk, single-crystal ZnO substrates by diffusion of P from a Zn 3 P 2 dopant source in a closed-ampoule system. Research task: Determine efficacy of pn homojunction for LED

14. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Electroluminescence From N+-Implanted Bulk ZnO Band-Edge Electroluminescence From N+-Implanted Bulk ZnO –Studies of phosphorus and nitrogen doping via ion implantation carried out. –Rectifying junctions and light emission realized. N+ ion implantation at moderate doses (10 12 -10 13 cm -2 ) into nominally undoped (n~10 17 cm -3 ) bulk single-crystal ZnO substrates followed by annealing in the range 600-950°C was used to fabricate diodes that show band-edge electroluminescence at 120K (~390 nm) under forward bias conditions. ZnO substrate N + implanted ZnO (300nm) Au (80nm) Ni (20nm) Au (200nm) Ti (20nm) hυ Research task: Achieve UV light emission from pn homojunction device

15. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 N-implanted ZnO crystals: Light Intensity Performance Devices 600C RTA 800C RTA 950C RTA P at 100mA (Lumen) 3.57×10 -9 8.5×10 -10 0 Onset > 8 volts

16. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Si diode test Light emission for diodes with onset>5 volts

17. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Attribute optical emission to high-field carrier injection Current focus is on pn junction heterostructure devices for minority carrier injection LED –Epitaxial ZnMgO doped with P or N High hole concentration –Formation of heterojunction device Minority carrier injection

18. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Vertical ZnO NWs/PEDOT LED Nanowire Array The cross section schematic of ZnO nanowires LED

19. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Efforts toward epitaxial light-emitting homojunction and/or heterojuction Multiple devices fabricated and tested –ZnO:P/ZnO:Ga/ZnO buffer/Al 2 O 3 –ZnO:P/ZnO:Ga/ZnO buffer/ZnO single crystal –ZnMgO:P/ZnO:Ga/ZnO buffer/Al 2 O 3 –ZnO:As/ZnO:Ga/ZnObuffer/Al 2 O 3 High leakage currents (non-rectifying I-V) observed as persistent limitation –Possible origins of leakage currents Leakage paths along ZnO surface due to processing-induced surface conduction P-type to n-type conversion of P-doped ZnO due to processing Pinholes in p-type layer due to surface roughness Efforts in Budget Period 3 will focus on identifying and eliminating cause(s) of leakage currents

20. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 3. ZnO:P 0.01 ( PL of p-type samples ) / cm 3 Ohm-cmCm 2 /v-sRTA 1.61E+1777.670.4998 950 ℃ ① ZP-4(950) (T g = 600 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 1.55E+1748.8270.8139 900 ℃ ② ZP-6(900) (T g = 700 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 2.37E+15801.363.2161 950 ℃ ③ ZP-6(950) (T g = 700 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 1.98E+1746.570.67867 900 ℃ ④ ZP-7(900) (T g = 800 ℃ ) Band edge PL and p-type seen in P-doped ZnO!

21. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ Zn 0.9 Mg 0.1 O:P 0.02 ( PL of p-type samples ) / cm 3 Ohm-cmCm 2 /v-sRTA 2.86E+15115160.1893as grown ① ZMP-3 (T g = 500 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 6.82E+15732.491.2349as grown / cm 3 Ohm-cmCm 2 /v-sRTA 7.78E+1757.3880.1382as grown ② ZMP-5 (T g = 600 ℃ ) : Not reproducible ③ ZMP-10 (T g = 550 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 1.02E+14121340.50579 700 ℃ ④ ZMP-3(700) (T g = 500 ℃ ) / cm 3 Ohm-cmCm 2 /v-sRTA 1.10E+155094.71.1135 800 ℃ ⑤ ZMP-6(800) (T g = 700 ℃ ) No evidence for band edge PL in ZnMgO:P films

22. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ① Good PL(small deep level) + low carrier density : FWHM = 0.229 ° : 1.07E+17 /cm 3, 36.44 cm 2 /v-s, 1.65 ohm-cm Growth condition : - Substrate : sapphire c-plane - Target : undoped ZnO - Laser : 350 mJ / 1Hz - Working pressure (O2 + O3 ) : 30 mTorr - Ablation time : 2 hr - Growth temperature : 800 ℃ Candidate “i” layer for p-i-n LED

23. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ② The lowest carrier density ( Still working ) – not completed : 1.99+16 /cm 3, 22.30 cm 2 /v-s, 15.75 ohm-cm ZnO epi-layer (0.4 ㎛ ) MgO buffer layer (~50nm) Sapphire c-plane Growth condition : - Substrate : sapphire c-plane - Target : undoped ZnO - Laser : 350 mJ / 1Hz - Working pressure (O2 + O3 ) : 30 mTorr - Ablation time : 2 hr - Growth temperature : 800 ℃ ( buffer layer : MgO at 450 ℃, P : 10 -4, time : 1 hr, 350 mJ/ 1Hz ) ( At many other conditions, the carrier density also shows low 16 ) MgO buffer: lowers background carrier density by factor of 5

24. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 2. Epi-layer - Laser : 350 mJ / 1Hz - Pressure (O2 + O3 ) : 30 mTorr - Temperature : 800 ℃ - Ablation time : 2 hr 1. Growth condition ZnO epi-layer (0.4 ㎛ ) ZnO buffer layer Sapphire c-plane 500 ℃ 800 ℃ 1. Buffer layer - Laser : 350 mJ / 1Hz - Pressure (O2 + O3 ) : 30 mTorr - Temperature : 500 ℃ - Ablation time : 2 hr ① 50 nm ② 100 nm ③ 200 nm ④ 300 nm Buffer Epi-layer Conditions for next slide

25. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Thickness of buffer layer (nm) Concentration (/cm 3 ) Mobility (cm 2 /v s) Resistivity (ohm cm) 504.35E+161.1130.70 1005.12E+160.523233.64 2002.88E+160.08242642.5 3002.16E+170.0414700.24 As grown1.07E+1736.441.65 MgO (~50nm)1.99E+1622.3015.75 3. Hall Low temp growth of ZnO buffer yields low mobility in undoped ZnO films

26. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ Growth conditions Sapphire Substrate Buffer layer (25nm) Undoped ZnO ( ~ 1um) ▶ Bulk layer growth - Target : undoped ZnO - T g : 850 ℃ - Pressure : 10 mTorr ( O 2 + O 3 mixture gas ) - Laser : 180 mJ / 4 Hz - Ablation time : 2 hrs 2 min ( 1.22 Å / s ) ▶ Buffer layer growth - Target : undoped ZnO - T g : 850 ℃ -Pressure ( O 2 + O 3 mixture gas ) ① without buffer ② 0.01 mTorr ③ 0.1 mTorr ④ 1 mTorr ⑤ 10 mTorr - Laser : 180 mJ / 1 Hz - Ablation time : 9 min ( 0.53 Å / s ) ● Characterization - XRD rocking curve - AFM - SEM - Optical microscopic - Hall - Thickness Conditions for next slide

27. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Working pressure of buffer layer (mTorr) Concentration (/cm 3 ) Mobility (cm 2 /v s) Resistivity (ohm cm) Without buffer1.6495E1873.610.05146 0.012.7502E1885.4760.02661 0.12.3765E1887.6060.03001 12.2949E1885.4430.03187 101.8874E1887.3710.03803 ◈ Hall ① Resistivity ② Carrier density ③ Mobility Excellent mobility for ZnO films!!!

28. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Growth temperature of the buffer layer ( ℃ ) Omega rocking FWHM (arcsec) 450 242.64 (0.0674°) 550 210.96 (0.0586°) 650 206.64 (0.0574°) 750 49.32 (0.0137°) 850 47.16 (0.0131°) ◈ FWHM of XRD rocking curve Low temperature nucleation yields poorer crystallinity

29. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Growth temperature of buffer layer ( ℃ ) Concentration (/cm 3 ) Mobility (cm 2 /v s) Resistivity (ohm cm) 4501.9011E+1865.6720.050127 5507.4896E+1783.3490.10035 6501.7959E+1873.5080.0437381 7508.5180E+1778.1110.084127 8502.2949E1885.4430.03187 ◈ Hall ① Resistivity ② Carrier density ③ Mobility Low temperature nucleation yields low mobility

30. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Optimized thick undoped ZnO films ◈ Growth conditions Sapphire Substrate Buffer layer (25nm) Undoped ZnO ( ~ 1um) ▶ Bulk layer growth - Target : undoped ZnO - T g : 650 ℃ - Pressure : 10 mTorr ( O 2 + O 3 mixture gas ) - Laser : 180 mJ / 4 Hz - Ablation time : 2 hrs 20 min ( 1.22 Å / s ) ▶ Buffer layer growth - Target : undoped ZnO - Pressure : 1m Torr ( O 2 + O 3 mixture gas ) - T g : 850 ℃ - Laser : 180 mJ / 1 Hz - Ablation time : 9 min ( 0.53 Å / s ) Conditions for next 2 slides

31. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ AFM ① 10 by 10 ㎛ ② 5 by 5 ㎛ ( rms : 3.323 nm) ( rms : 1.557 nm) 50 nm 30 nm

32. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ Omega Rocking Curve ◈ Hall data : 2.3971E+16 ( /cm 3 ),87.68 ( cm 2 /vs ), 3.1217 ( ohmcm )

33. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 N-type ZnO films ( Ga v.s. Al ) ◈ Growth condition ◈ Surface morphology - OM - AFM ◈ Crystallinity - XRD rocking curve (FWHM) ◈ Electrical properties - Hall measurement

34. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ Growth conditions ▶ n-type Bulk layer growth -Target : ① ZnO : Al (0.01 at %) ② ZnO : Ga (0.01 at %) - T g : 650 ℃ - Pressure : 10 mTorr ( O 2 + O 3 mixture gas ) - Laser : 180 mJ / 4 Hz - Ablation time : 2 hrs 20 min ( 1.22 Å / s ) ▶ ZnO Buffer layer growth - Target : undoped ZnO - Pressure : 1m Torr ( O 2 + O 3 mixture gas ) - T g : 850 ℃ - Laser : 180 mJ / 1 Hz - Ablation time : 9 min ( 0.53 Å / s ) Sapphire Substrate ZnO buffer layer (25nm) ① ZnO : Al (0.01 at %) ② ZnO : Ga (0.01 at %) ( ~ 1um)

35. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 ◈ AFM ① ZnO:Al ② ZnO:Ga Roughness rms : 14.174 nm ) ( Roughness rms : 4.546 nm ) 100 nm 50 nm

36. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Roughness rms (nm) ZnO:Al14.174 ZnO:Ga4.546 ◈ Roughness rms ( 10 ㎛ X 10 ㎛ ) ◈ FWHM of XRD rocking curve Concentration (/cm 3 ) Mobility (cm 2 /v s) Resistivity (ohm cm) ZnO:Al1.4050E+1927.3630.016231 ZnO:Ga6.8788E+1820.9270.043497 ◈ Hall Omega rocking curve - FWHM (arcsec) ZnO:Al700 (0.1945°) ZnO:Ga513 (0.1425°)

37. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 1. SEM images ( ZLP-19, Tg = 700 ℃, 50mTorr ) + Tube furnace annealing (700 ℃, 1hr) ( ZnO:P / ZnO:Ga / ZnO thin buffer / Sapphire c-plane) Evidence for particle growth upon annealing of Ga-doped ZnO?

38. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 pn junction formation and properties

39. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 IV for ZnMgO:P/ZnO junctions Rectifying junctions with 3-4 V turn-on

40. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 After annealing Conductivity of N-type 500nm ZnMgO:P/200nm undoped ZnO buffer layer/sapphire Annealing temperature 600 o C700 o C800 o C 700 o C ZnMgO:P Increase (current: 8*10 -10 to 3*10 -9 at 5V) Decrease (current: 1*10 -8 to 3*10 -9 at 5V) Decrease (current: 1.5*10 -8 to 4*10 -9 at 5V) 800 o C ZnMgO:P Increase (current: 4*10 -9 to 1.7*10 -7 at 5V) Increase (current: 6*10 -12 to 7*10 -8 at 5V) Increase (current: 4*10 -12 to 6*10 -8 at 5V) 900 o C ZnMgO:P Increase (current: 5*10 -12 to 3*10 -8 at 5V) Increase (current: 3.5*10 -12 to 2.5*10 -10 at 5V) Increase (current: 6*10 -12 to 2.8*10 -10 at 5V ) Rectifying turn-on at 3-4 volts

41. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Annealing ZnMgO:P/ZnO/Al2O3 junctions After annealing conductivity 600 o C700 o C800 o C 30 nm ZnOincreaseincrease(current: 10 -8 to 10 -7 at -5V)increase 100 nm ZnOdecreaseincrease(current: 1.5*10 -8 to 4*10 -8 at -5V)decrease 200 nm ZnOdecrease decrease(current: 10 -8 to 10 -9 at -5V) 400 nm ZnOdecrease decrease(current: 10 -5 to 10 -9 at -5V) 600C ZnMgO:Pdecrease decrease(current: 10 -6 to 10 -9 at -5V)

42. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 CuCrO 2 : possible alternative p-type oxide for hole injection Epitaxial film growth achieved Mg doping reported to produce p-type conductivity Research task: Investigate alternative p-type oxides as hole injection materials

43. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Research task: Investigate alternative p-type oxides as hole injection materials Ga-doped SnO 2 Hall measurements: P-type Hole concentration 2x10 19 cm -3 (possible IP)

44. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Changes to baseline plan in Budget Period 2 Experimental emphasis on epitaxial films on sapphire Explored alternative p-type oxides as hole injectors Explored light emission from implanted ZnO and nanowires

45. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Relationship of Budget Period 2 Tasks to Project Success Task descriptionSpecific activitiesRelationship to overall project mission Growth of p-type (Zn,Mg)O films Growth of phosphorus, arsenic, copper doped (Zn,Mg)O films Photoluminescence studies of P-, As- doped ZnMgO films Hall measurements of films Annealing studies Thin films needed for light-emitting pn junction devices Formation of pn homojunction thin film structure Grew (Zn,Mg)O pn junction structures on sapphire Grew (Zn,Mg)O pn junction structures on single crystal ZnO substrates Proof of concept device structure for eventual heterostructure devices Fabrication of pn homojunction device Identified materials and processes for ohmic contacts Identify processes for dry etching Necessary for LED synthesis Characterization of pn homojunction Measured IV characteristics Investigate light emission from junctions Understanding of pn junction properties and performance Growth of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterostructure Grew multiple structuresTarget device structure of program Fabrication of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterojunction devices Identified materials and processes for ohmic contacts Identify processes for dry etching Target device structure of program

46. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Status of project milestones in Budget Period 2 TitleMetric/Method of VerificationMilestone Status Growth of p-type (Zn,Mg)O filmsAchieve 10E17 cm-3 p-type carrier density in ZnO film Completed Formation of pn homojunction thin film structure Optimize crystalline/polycrystalline pn junction structure film growth process with respect to IV Demonstrated non-linear IV for epitaxial and diffused samples. Need better understanding of pn junction formation Fabrication of pn homojunction deviceAchieve UV light emission from pn homojunction device Electroluminescence achieved for N- implanted ZnO crystals and ZnO nanowires the p-type polymer. Additional work need for epitaxial light emitting junctions. Focus is on P:ZnO/Ga:ZnO junctions Characterization of pn homojunctionDetermine efficacy of pn homojunction for LED Additional work needed to achieve band-edge EL due to minority carrier injection Growth of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterostructure Optimization of epitaxial heterostructure thin film junction Highly crystalline buffer layer developed. Fabrication of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterojunction devices Achieve nonlinear rectifying IV in pn heterojunction device Processing of mesa structures demonstrated. Metal contact technology developed

47. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Status of project milestones in Budget Period 3 Task TitleMetric/Method of VerificationStatus Growth of p-type (Zn,Mg)O filmsAchieve 10E18 cm-3 p-type carrier density in ZnO film Ongoing Continue to explore P, As, N as acceptor dopants Formation of pn homojunction thin film structure Optimize polycrystalline pn junction structure film growth process with respect to IV Lower priority Proof of concept needed on epitaxial structures Fabrication of pn homojunction deviceAchieve UV light emission from pn homojunction device Ongoing Focusing on structures on single crystal ZnO substrates Characterization of pn homojunctionDetermine efficacy of pn homojunction for LED Ongoing Growth of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterostructure Optimization of epitaxial heterostructure thin film junction Ongoing Optimization of polycrystalline heterostructure thin film junction Lower priority Fabrication of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterojunction devices Achieve nonlinear rectifying in pn heterojunction device Device fabrication protocol estabilshed Achieve UV light emission from pn heterojunction Ongoing

48. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Status of project milestones in Budget Period 3 (continued) Task TitleMetric/Method of VerificationStatus Characterization of p-(Zn,Mg)O/ZnO/n- (Zn,Mg)O pn heterojunction devices Identify limiting factors for IV nonlinearity and band-edge emission in biased pn heterojunction Ongoing Determine the efficacy of pn heterojunction for LED-based lighting Ongoing Growth of p-CuGaO 2 /n-ZnO pn heterostructure Achieve 10E18 cm-3 p-type carrier density in epitaxial CuGaO 2 film Experiments shifted to CuCrO 2 and SnO 2 epitaxial films as possible p- type hole injectors Optimize epitaxial p-CuGaO 2 /n-ZnO junction structure To be initiated in Budget Period 3 with CuCrO 2 and SnO 2 Fabrication of CuGaO 2 /ZnO heterojunction devices Achieve nonlinear rectifying in pn CuGaO 2 /n-ZnO heterojunction device To be initiated in Budget Period 3 with CuCrO 2 and SnO 2 Achieve UV light emission from a CuGaO 2 /ZnO pn heterojunction To be initiated in Budget Period 3 with CuCrO 2 and SnO 2 Characterization of p-CuGaO 2 /n-ZnO devices Determine the efficacy of p-CuGaO2/n- ZnO LED devices for solid state lighting To be initiated in Budget Period 3 with CuCrO 2 and SnO 2

49. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Justification for continuation of project Progress made towards all milestones for Budget Period 2 –Achieved p-type ZnO with p = mid-10 17 /cm 3 –Light emission observed from implanted junctions –Homo- and heterojunction device fabrication process established –Epitaxy of alternative p-type hole injection material identified Original justification for project (promise of ZnO for light emitting diodes) remains valid –Reports in Applied Physics Letters of light emission in As-doped ZnBeO LED

50. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Onset of non- linear IV at 10 V, not 3.2 V EL seen with current > 10 mA

51. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Advance Material, 2006. ZnO LED Results for Other Groups p-n LED Using Sputtering [Jae-Hong Lim et al.] Well-defined IV onset at ~ 3.2 V

52. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Characterization of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterojunction devices (Ren) Fab. of CuGaO2/ZnO heterojunction devices (Pearton) Growth of p-CuGaO2/n-ZnO pn heterostructure (Ren) Characterization of p-CuGaO2/n-ZnO devices (Ren) Fab of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterojunction devices (Pearton) Growth of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterostructure (Norton) Characterization of pn homojunction (Ren) Fabrication of pn homojunction device (Pearton) Formation of pn homojunction (Norton) Growth of p-type (Zn,Mg)O films (Norton) Year 1Year 2Year 3 Overview of remaining Budget Periods

53. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Characterization of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterojunction devices (Ren) Fab. of CuGaO2/ZnO heterojunction devices (Pearton) Growth of p-CuGaO2/n-ZnO pn heterostructure (Norton) Characterization of p-CuGaO2/n-ZnO devices (Ren) Fab of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterojunction devices (Pearton) Growth of p-(Zn,Mg)O/ZnO/n-(Zn,Mg)O pn heterostructure (Norton) Characterization of pn homojunction (Reen) Fabrication of pn homojunction device (Pearton) Formation of pn homojunction (Norton) Growth of p-type (Zn,Mg)O films (Norton) ID Limiting factors for band-edge emission 10E17 cm-3 p-type carrier density 10E18 cm-3 p-type carrier density 10E16 cm-3 p-type carrier density Efficacy of p-CuGaO2/n-ZnO LED Determine efficacy of pn homojunction for LED Rectifying pn homojunction Optimize epi junction structure Rectifying epitaxial pn heterojunction ID limiting factors for band-edge emission Efficacy of pn heterojunction for LED Optimize poly junction structure 10E18 cm-3 p-type carrier density Optimize epi junction structure Rectifying pn junction Light emitting pn homojunction Light emitting pn heterojunction Year 1Year 2Year 3

54. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 DELIVERABLES –The recipient will provide periodic, topical and final reports in accordance with the “Federal Assistance reporting Checklist” provided with the program solicitation. –The recipient will provide monthly e-mail correspondence with the program manager that will indicate task and subtask updates, expanded summary of project results, key milestones and significant accomplishments, presentations and publications, site visit and travel descriptions. The recipient will also provide briefings for presentation upon request. –The recipient will present a technical paper at the DOE/NETL Annual Contractor’s Review Meeting.

55. ZnO LEDs for Solid State Lighting Budget Period Review Sept 14, 2006 Final product/commercialization Objective of project is to realized viable LED technology based on ZnO pn heterojunction Commercialization would be through a yet to be determined industrial partner