SPONTANEOUS AND STIMULATED EMISSION OF ZnO NANORODS OF DIFFERENT SHAPE

Transcription

1 SPONTANEOUS AND STIMULATED EMISSION OF ZnO NANORODS OF DIFFERENT SHAPE A.N. Gruzintsev, A.N. Redkin,**G.A. Emelchenko, *C. Barthou Institute of Microelectronics Technology, Russian Academy of Sciences, , Chernogolovka, Moscow distr., Russia. *Institute d NanoScience, UMR-CNRS 7601 Université P. et M. Curie, Case 80, 4 Place Jussieu, PARIS CEDEX 05, France. **Institute of Solid State Physics Russian Academy of Science, Chernogolovka, Moscow distr., Russia

2 Contents Introduction ZnO nanorods synthesis Annealing influence Luminescent properties Stimulated emission Conclusions

3 Introduction ZnO nanorods have potential application in fabricating of cold cathode electron source, nanotransistors and gas sensors. The array of the ZnO quantum nanorods, obtained on the silicium (111) or (100) substrates, as UV-photodetectors. Far-field PL spectra for different shape nanorods at various excitation power densities are presented. ZnO nanorods are perspective for shortwavelength nanolasers.

4 ZnO nanorods synthesis The ZnO nanorods were synthesized using a vapor phase transport process, without an Au thin film catalyzing The synthesis of the ZnO nanorods was also conducted by aqueous thermal decomposition of the Zn +2 amino complex [1] [1] L. Vayssieres, K. Keis, S.-E. Lindquist and A. Hagfeldt. J.Phys.Chem. B2001, 105,

5 Chemical Vapor Deposition end of tube beginning Samples O2 Quarts tube heating Substrates Si (111) Zn The zinc evaporation temperature was T 3 = C, the synthesis temperature (first zone) was T 1 =620 C. The pressure in the reactor was maintained at the level of 5 torr. The synthesis was normally conducted within

6 Chemical solution method Quartz vessel with lid containing a fused silica or silicon (100) substrates and an equimolar (0.1M) aqueous solution of zinc nitrate, Zn(NO 3 ) 2 *4H 2 O, and methenamine, C 6 H 12 N 4, was heated at 95 O C for 2 10 h. Subsequently, thin films washed with deionized water to remove residual solution and allowed to dry in air at room temperature. The zinc oxide nanowires showed vertically and horizontally aligned morphologies in different growth regimes.

7 SEM images ZnO-self organization CVD nanorods on Si (111) -620 C I T 3 =670 C in end of tube II T 3 =670 C in beginning nm mkm

8 SEM images Nanopyramides in different places of tube T syn =T1=620 C mkm mkm III T 3 =640 C in beginning IV T 3 =640 C in end of tube

9 --- 2 mkm SEM images In different places of tube T 3 =670 C SEM images of ZnO nanocrystals obtained at T 1 =650 C. 9

10 Luminescent properties CVD ZnO nanorods Luminescence of ZnO type-i samples by nitrogen laser nm excitation with different power. ZnO Ax14-1.OPJ (G1) Intensity (rel.) KW/cm 2 1E-2 1E λ (nm) T=300K

11 Luminescent properties CVD ZnO nanorods Luminescence of ZnO type-ii samples by nitrogen laser nm excitation with different power. ZnO AX15-1.OPJ (G2) Intensity (rel.) ,1 0, KW/cm 2 1E λ (nm) T=300K

12 Luminescent properties CVD ZnO nanopyramides Luminescence of ZnO type-iii samples by nitrogen laser nm excitation with different power KW/cm 2 ZnO AX73&74-1.OPJ (G2) Intensity (rel.) 1 0,1 0,01 1E-3 1E λ (nm) T=300K

13 Luminescent properties CVD ZnO nanopyramides Luminescence of ZnO type-iv samples by nitrogen laser nm excitation with different power. Intensity (rel.) ,1 0,01 ZnO KW/cm 2 AX73&74-1.OPJ (G5) 1E λ (nm) T=300K

14 Luminescent properties -The analysis of the mechanisms of radiative recombination in the processes of lasing, using the wavelength of the maxima of the corresponding lines, has shown that in nanorods the recombination of interacting free excitons dominates whereas in nanopyramides the recombination of electron-hole plasma does. -Changes in the intensity of the spontaneous luminescence of free excitons bear witness to a more perfect crystalline structure of nanorods.

15 CVD on Si(111) substrates The dependence of shape and size of the ZnO nanocrystals on the position of the substrate in the quartz tube with respect to the source of zinc. The dependence of shape and size on the zinc evaporation temperature and the synthesis temperature (first zone).

16 CVD on Si(111) substrates The mode structure of the laser emission from the above obtained nanoresonators is also of scientific interest. Despite rather chaotic distribution of ZnO rods by direction, we can, by selective optical excitation with polarized light of a nitrogen laser, distinguish only a part of them oriented along the exciting laser electric field. Having lower pumping thresholds, ZnO nanorods yield stimulated luminescence lengthwise the rod axis.

17 PL Mode structure of Lasing Z angel 2 4 The intensity of the stimulated luminescence VS the angle-z between the longitudinal rod axis and the signal registration direction for the samples of type: I(1), II(2), III(3),IV(4). The pumping power is threshold for each type. T=300K.

18 CVD on Si(100) substrates -Nanorods of zinc oxide were grown on a substrate using the method of chemical vapour deposition (CVD) at a reduced pressure. The initial reagents were metallic zinc of high purity (99.999%) and an oxygen-nitrogen mixture (20% oxygen). -The synthesis was conducted in a two-zone quartz reactor flowing type. Zinc evaporation took place in the three zone. In the second zone zinc vapours interacted with oxygen. The substrates, i.e. silicon platelets oriented (100), were arranged in first zone. -The zinc evaporation temperature was 650 C, the synthesis temperature (first zone) was 670 C. The consumption of the oxygen-nitrogen mixture was 1 l/h. The pressure in the reactor was maintained at the level of 5 torr. The synthesis was normally conducted within 30 minutes.

19 SEM images of sample N mkm Fig.1 SEM images of ZnO nanorods from the end of tube.

20 Fig.2 SEM images of ZnO nanorods from beginning of tube. SEM images of sample N mkm

21 SEM images GaN nanowires on Au points Fig.3 SEM images of GaN nanowires nm

22 Luminescent properties а) PL of GaN nanowires on Au pointes GaN wires

23 Luminescent properties Free excitons Intensity (arb. units) Different places in the tube T=300K DAP Wavelenght (nm)

24 Chemical solution method ZnO nanorods on Si(100) substrate mkm mkm

25 ZnO nanorods: : thermal stability and exciton emission efficiency Array of ZnO single crystal nanorods produced by thermal decomposition of Zn +2 -amino complex on Si substrate. Composite: ZnO nanorods - SiO 2 nanoparticles mkm

26 ZnO nanorods annealing in air DAP PL Intensity arb.units ZnO-rods excitons ish W avelength,nm 200 initial Chemical solution T=300K

27 Enhancement of the exciton emission at N 2 -pulse laser pumping. 200 C/1 h in air Thermal stability: heat treatment at 700 o C/1 h in air. Composite: 250 ZnO nanorods - SiO 2 nanoparticles. 200 Exciton Photoluminescence, arb. un Array of ZnO nanorods Photoluminescence, arb. un Composite: ZnO - SiO 2 Array of ZnO nanorods Donor-acceptor recombination Wavelength, nm Wavelength, nm

28 Conclusions This natural cavity or waveguide formation in ZnO nanorods suggests a simple chemical approach to forming a laser resonators without cleavage and etching. In fact, the good monocrystal quality and UV exciton photouminescence were observed for these ZnO nanorods at room temperature. The stimulated UV emission, related with the photon binding modes of the ZnO nanorods, been observed by increasing of the optical pumped power.