Highly efficient photo emitters and detectors by oxide based nanostructures

Transcription

1 MICINN JST Joint Workshop Barcelona Spain March, 2010 Highly efficient photo emitters and detectors by oxide based nanostructures Atsushi Nakamura Research Institute of Electronics Shizuoka University Johoku, Hamamatsu, Japan 1

2 Outline Introduction Wide bandgap semiconductors ZnO based nanostructure motivation MOCVD growth Bandgap engineering Hetero structures Challenge to p type Collaboration Conclusions 2

3 Wide Bandgap Semiconductors 8 7 MgO(r) GaN (AlGaN, InGaN, AlGaInN) 6 BN C AlN(h) ZnO (MgZnO, ZnCdO, MgZnCdO) Energy Gap (ev) GaN(h) 4H-SiC(h) 6H-SiC(h) 3C-SiC(c) ZnO(h) CdO(r) InN(h) ZnS GaP GaAs Si MgS ZnSe MgSe InP ZnTe CdSe InAs CdTe Bond length (A) ZnO Wurtzite Hexagonal a= nm c= nm MgO Rock salt Cubic a= nm CdO Rock salt Cubic a= 0.47 nm 3

4 ZnO based nanostructure self assembled ZnO nano structures nano dots, nano wires, nano rods, nano tubes various applications nanoscale optical devices large exciton binding energy =60meV biexciton binding energy =15meV size manipulation exciton Bohr radius Table I. Exciton Bohr radius and band gap energies for various semiconductors Semiconductor Exciton Bohr radius (nm) Bandgap energy (ev) ZnO GaN GaAs G. Zhang, A. Nakamura et al, Appl. Phys. Lett., 89, (2006) G. Zhang, A. Nakamura et al, Jpn J. Appl. Phys., 46, L730 (2007) 4

5 Motivation Nanoscience and New Materials for Environmental Challenges Highly efficient photo emitters and detectors by oxide based nanostructures p n heterojunctions in nanocolumns Electroluminescence in UV spectrum UV nano sensors Breakthrough/Issues lack of p type 5

6 Growth method RPE MOCVD O2 (O2, N2) DEZn, DMCd Vacuum EtCp2Mg Schematic drawing of remote plasma enhanced MOCVD system MOCVD systems Vertical type: remote plasma Vertical type: remote plasma, Hot wire Horizontal type: remote plasma Radical alloying doping low temperature growth polar, nonpolar orientation MO sources, gas DEZn DMCd EtCp 2 Mg TMI (DIBM) 2 Cu Oxygen, Hydrogen, Nitrogen, H 2 O 2 6

7 Bandgap engineering 7

8 Mg x Zn 1 x O alloying 8

9 Zn 1 x Cd x O alloying S. Shigemori, A. Nakamura et al, Jpn J. Appl. Phys., 43, L1088 (2004) J. Ishihara, A. Nakamura et al, Appl. Phys. Lett., 89, (2006) 9

10 μ PL spectra 4K Zn0.96Cd0.04O (900nmt)/a sapphire 1cm 100W/cm cm 4 3 A. Nakamura et al, Jpn. J. Appl. Phys., 44, L4 (2005) 10

11 Summary of Bandgap Engineering 4.0 MgyZn1-yO ZnO Zn1-xCdxO Bandgap energy (ev) Content, x, y K. Yamamoto, A. Nakamura et al, J. Cryst. Growth, in press 11

12 Heterostructures 12

13 DH PL temperature dependence ZnO 15nm 3.4 Zn0.92Cd0.08O 30nm ZnO 200nm 3.3 PL Intensity (arb. units) a sapphire sub. 20 K 100 K 120 K 150 K 180 K 240 K 278 K PL peak energy (ev) Barrier (ZnO) sub-peak Zn0.92Cd0.08O Photon Energy (ev) Temperature (K) A. Nakamura et al, Jpn. J. Appl. Phys., 44, L4 (2005) 13

14 DH PL 10 6 ZnO@20K ZnCdO@20K ZnO@RT ZnCdO@RT PL Intensity (arb. units) 3.0 mw 2.0 mw 1.0 mw 0.5 mw 0.2 mw Log of PL Intensity (arb. units) s=1.1 s=1.1 s=1.2 s= Photon energy (ev) Excitation Intensity (mw) A. Nakamura et al, Jpn. J. Appl. Phys., 44, L4 (2005) 14

15 Heterojunction LEDs Current density (A/cm 2 ) Indium n contact n ZnO (10nm) n MgyZn1 yo (400nm) n Zn1 xcdxo (200nm) p 4H SiC (300μm) Gold p contact Normarized EL Intensity (arb. units) x 35 x Voltage (V) I V characteristic of DH LED at room temperature Wavelength (nm) Normalized EL spectra of DH LED at room temperature. A. Nakamura et al, Appl. Phys. Lett., 90, (2007) 15

16 Multilayered White LEDs ZnO contact Mg x Zn 1 x O Barrier Incandescent lamp Zn 1 x Cd x O yellow Zn 1 x Cd x O blue p 4H SiC EL Intensity (arb. unit) White LED Wavelength (nm) 16

17 Photo detectors 17

18 Au Schottky diodes Peroxide surface treatment non treatment 10-4 Current (A) H 2 O 2 treatment as grown H 2 O 2 treated Voltage (V) A. Nakamura et al, J. Korean Phys. Soc., 53, 2909 (2008) 18

19 Spectral response of Responsivity ( A/W) Mg x Zn 1 x O Schottky Photodiodes 200μmφ Top view Ohmic contact Schottky contact (semi transparent) Cross view 5.6 % Mg 9.5 % Mg 14.5 % Mg 18.0 % Mg In collaboration with: UPM ISOM Energy (ev) 19 A. Hierro, A. Nakamura et al, Appl. Phys. Lett., 94, (2009)

20 Nanowire photodetector In collaboration with: UPM ISOM 10-8 Under hυ>e g illumination Current (A) In the dark Voltage (V) 20

21 Challenge to p type ZnO 21

22 Concepts of realizing p type ZnO Fundamental study of ZnO Polar, nonpolar orientation Ion implantation, defects, dopants, theoretical models ZnO based new component material ZnO In 2 O 3 ZnO Cu 2 O Collaboration (consortium) Universidad Politécnica de Madrid (UPM) Center for Microanalysis of Materials Universidad Autónoma de Madrid (UAM CMAM) 22

23 Non polar orientation, nitrogen doping XPS analysis; polar ZnO:N (0001) / a plane (11 20) sapphire substrate nonpolar ZnO:N (11 20) / r plane (10 12) sapphire substrate Intensity (arb. unit) As-grown (1) (2) (1) Non-polar ZnO:N (2) Polar ZnO:N N (1s) Intensity (arb. unit) Annealed (1) (2) (1) Non-polar ZnO:N (2) Polar ZnO:N N (1s) Binding energy (ev) Binding energy (ev) 394 S. Gangil, A. Nakamura et al, Jpn J. Appl. Phys., 46, L549 (2007) 23

24 Acceptors in Mg x Zn 1 x O;DLOS analysis 10 9 RT V appl =0V In collaboration with: UPM ISOM 8 x= x= ΔC/C E V +280meV E V +580meV x=0.096 N D -N A (cm -3 ) x= Energy (ev) Mg content, x acceptor like behavior carrier compensation A. Hierro, A. Nakamura et al, Appl. Phys. Lett., 94, (2009) 24

25 New family MgZnO:In Mg 0.05 Zn 0.95 O:In In collaboration with: UAM CMAM, UPM ISOM 0.0% 0.5% 1.0% 3.0% 500nm ZnO:In 500n m 0.0% 0.5% 1.0% 3.0% 500nm occupying substitutional place 500n m T. Tsuboi, A. Nakamura et al, Jpn J. Appl. Phys., in press 25

26 New family ZnCuO (10-10) CuO (100) (0002) (10-11) a-sapphire (11-20) 2θ (degree) x= x=0.02 x=0.003 x= θ (degree) Intensity (arb. units) (100) 32.4 o (002) 35.5 o (111) 36.4 o (111) 38.7 o (200) 42.3 o Bandgap (ev) Cu 2 O CuO Cu content, x Intensity (arb. units) c axis length (nm) B. Hu, A. Nakamura et al, Physica Status Solidi (c), in press 26

27 Conclusions ZnO based oxide semiconductors old but new materials Bandgap engineering Hetero structures Visible LEDs,,, UV LED? Challenge to p type new materials collaborations 27

28 Acknowledgements Members/Collaborators Our team at RIE, Shizuoka University: J. Temmyo G. Zhang, S. Gangil, S. Shigemori, J. Ishihara, T. Ohashi, T. Tsuboi, B. Hu K. Yamamoto Cooperation with UPM ISOM, UAM CMAM: E. Muñoz A. Hierro J M. Ulloa, A. Redondo, G. Tabares, C. Rivera, A. Navarro, J. Pereiro 28