Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology

Transcription

1 Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology Friederich Limbach 1/33

2 Motivation Monolithic integration of III-V optoelectronic devices with Si based MOS technology allows an enrichment of functionality On-chip control of light emission in the visible range is possible through the use of nitride semiconductors Difficulties in achieving integration with nitrides: Lattice mismatch between Si and nitride semiconductors Thermal budget of MOS components to low for nitride based components P. Yang, Nano Lett., 10, (2010) 2/33

3 Approach: Nanowire based LEDs Advantages of nanowires High crystal quality on foreign substrates Elastic relaxation of strain and stress in heterostructures Molecular beam epitaxy: thermal budget of Si devices is obeyed GaN Si 10 nm E. Calleja et al. Phys. Status Solidi B, 244(8), (2007) J. Lähnemann et al. Phys. Rev. B, 84, (2011) R. Waser, Nanoelectronics and Information Technology (2005) 3/33

4 Outline I. Nanowire LED growth Model of nanowire growth Doping of GaN nanowires with Mg Active (In,Ga)N region Growth and processing of nanowire LEDs Electrical and optical device characterization E II. Nanowire LEDs and MOSFETs Integration with Si-MOS technology 4/33

5 Self-induced GaN nanowires grown by plasma-assisted molecular beam epitaxy 100 nm Impinging Ga flux 1 µm Sidewall diffusion Desorption Coalescence Surface diffusion Substrate Stable nucleus R. Caterino, Master thesis, Tor Vergata Uni. Rome (2009) 5/33

6 Growth of Mg-doped GaN nanowires without Mg supply with Mg supply Enhanced radial growth More coalescence Coverage: 50% Coverage: 77% F. Limbach et al. AIP Adv. 2, 1, (2012) 6/33

7 Growth of Mg-doped GaN nanowires QMS Line-of-sight quadrupole spectrometry aperture desorbing Ga impinging impingin Ga + N Ga + N F. Limbach et al. AIP Adv. 2, 1, (2012) substrate 7/33

8 Nucleation of Mg-doped GaN nanowires pressure [mbar] Ga 1.5x10-10 GaN 1.0x x p inc p diff p stab τ p(t 1 ) p(t 2 ) GaN:Mg time [min] Mg promotes rapid nucleation: Number of nuclei per time increased Line-of-sight quadrupole QMS spectrometry aperture desorbing Ga impinging impingin Ga + N Ga + N F. Limbach et al. AIP Adv. 2, 1, (2012) substrate 8/33

9 Nucleation of Mg-doped GaN nanowires pressure [mbar] Ga 1.5x10-10 GaN 1.0x x p diff p stab τ p inc p(t 1 ) p(t 2 ) GaN:Mg time [min] Number of nuclei (n * ) formed per unit time is increased through lowering of the barrier (ΔG * ): Mg promotes rapid nucleation: Number of nuclei per time increased T S range: 760 C C 10 3 E GaN = 4.0 ± 0.3 ev τ [s] 10 2 GaN:Mg GaN F. Limbach et al. AIP Adv. 2, 1, (2012) 10 1 E GaN:Mg = 3.2 ± 0.3 ev T -1 S [10-4 K -1 ] 9/33

10 n-i-p vs. p-i-n diodes in GaN nanowires Mg top Si top GaN:Mg GaN:Si GaN GaN GaN:Si GaN:Mg Si Si Si 10/33

11 n-i-p vs. p-i-n diodes: Ensemble photoluminescence Donor-Acceptor-Pair (DAP) emission indicates Mg incorporation and differs between Mg and Si on top Intensity [counts / s] T= 4K Si on top 20 mw/cm² 20 mw/cm -2 Mg on top type B type A Energy [ev] F. Limbach et al. J. Optoelect. Advan. Mat. 12, (2010). F. Limbach et al., submitted to Appl. Phys. Lett. (2012). 11/33

12 n-i-p vs. p-i-n diodes: Ensemble photoluminescence Donor-Acceptor-Pair (DAP) emission indicates Mg incorporation and differs between Mg and Si on top Mg on top: An acceptor-bound exciton (ABE) emission is detected Intensity [counts / s] / s] Si on top type B mev 2.8 mev ABE ev 1.9 mev Mg on top type A DBEeV 2.3 mev Energy [ev] Energy [ev] Intensity [counts / s] F. Limbach et al. J. Optoelect. Advan. Mat. 12, (2010). F. Limbach et al., submitted to Appl. Phys. Lett. (2012) T= 4K 20 mw/cm -2 Mg on top type B 20 mw/cm² type A Energy [ev] Si on top Mg incorporation as an acceptor is difficult if the p-type section is grown in the initial phase of the growth 12/33

13 Optical properties of the active region norm. intensity [arb. units] InN GaN T S = 475 C T S = 780 C InGaN InGaN T S = 580 C T S = 630 C energy [ev] Photoluminescence peak position can be controlled via the substrate temperature F. Limbach et al. J. Appl. Phys. 109, (2011) 13/33

14 Outline I. Nanowire LED growth Model of nanowire growth Doping of GaN nanowires with Mg Active (In,Ga)N region Growth and processing of nanowire LEDs Electrical and optical device characterization E II. Nanowire LEDs and MOSFETs Integration with Si-MOS technology 14/33

15 Growth of the nanowire LED structure Nanowire morphology was retained Cathodoluminescence confirms nominal growth sequence p-gan InGaN n-gan 400 nm Cathodoluminescence linescan 15/33

16 Processing of the as-grown GaN-NW LEDs MBE growth of the NW-LED structure Filling with spin-on-glass Etching of spin-on-glass covering the NW tips Metallization with semitransparent and thick bonding contacts 16/33

17 Electrical characteristics of the processed nanowire ensemble A = 0.53 mm² 5 V 8 V Turn-on voltage (V to ): 5.6 V 5 Current (ma) Bias (V) V to 17/33

18 Electrical characteristics of the processed nanowire ensemble Turn-on voltage (V to ): 5.6 V Parallel resistance (R p ): 27.8 MΩ Current (ma) Current (ma) Bias (V) Bias (V) V to 18/33

19 Electrical characteristics of the processed nanowire ensemble Turn-on voltage (V to ): 5.6 V Parallel resistance (R p ): 27.8 MΩ Series resistance (R S ): 220 Ω Ideality factor (n ideal ): Current (ma) Bias (V) I du/di (V) Current (ma) 19/33

20 µ-electroluminescence of the processed nanowire ensemble 10 V Multiple isolated luminescence spots Multiple colors, green emission dominates All spot sizes are diffraction-limited Luminescent point density is currentdependent and much lower than wire density ( 1%) 20/33

21 Origin of the dark regions X Electrical connection (NW length plays a role) X Efficiency of the quantum wells in the individual LEDs may differ Individual series resistances differ significantly and dominate the device performance 21/33

22 Outline I. Nanowire LED growth Model of NW growth Doping of GaN nanowires with Mg Active (In,Ga)N region Growth and processing of nanowire LEDs Electrical and optical device characterization E II. nanowire LEDs and MOSFETs Integration with Si-MOS technology 22/33

23 Integration of III-V nanotechnology with standard Si based MOSFET technology MOSFET D Gate S n-si 23/33

24 Integration of III-V nanotechnology with standard Si based MOSFET technology NW-LED MOSFET D Gate S n-si 24/33

25 Integration of III-V nanotechnology with standard Si based MOSFET technology NW-LED MOSFET D Gate S n-si 25/33

26 MOSFET and diode characteristics MOSFET Transistor is working High gate voltages are necessary current I SD [ma] V g = -16 V V g = -15 V bias U SD [V] V g = -17 V 26/33

27 MOSFET and diode characteristics current [ma] MOSFET Transistor is working High gate voltages are necessary bias [V] current I SD [ma] V g = -16 V V g = -15 V NW diode bias U SD [V] Rectifying characteristics Higher turn-on voltage V g = -17 V 27/33

28 MOSFET fabrication followed by NW LED growth NW-LED 200 µm 200 µm S Gate D 10 V Electroluminescence shifted compared with samples without FETs Underlying structures inhibit luminescence EL Intensity [arb. units] ma 30 ma ma 0 ma Wavelength [nm] 28/33

29 Switching of the diode via a MOSFET on the same substrate Coupling via external cables Current begins to flow as the channel in the FET is created Saturation at the expected current for the applied source drain voltage 8 I LED [ma] V g [V] 29/33

30 Conclusion Growth can be controlled under the supply of both doping species; (In,Ga)N quantum wells can be created and controlled τ [s] GaN:Mg GaN Processing an LED from a nanowire ensemble has been achieved T -1 S [10-4 K -1 ] current [ma] Several individual NW LEDs are contacted in parallel bias [V] Device characteristics dominated by individual series resistances 8 Integration of III-N NW LEDs and Si- MOSFET technology has been demonstrated I LED [ma] V g [V] 30/33

31 Outlook NW LED on drain region gate source 31/33

32 Outlook Selective area growth of NW-LED structures T. Gotschke et al. Appl. Phys. Lett. 98, 10, (2011) T. Gotschke PhD. thesis, HU Berlin (2012) T. Schumann et al., Nanotechnology, 22, 9, (2011) 32/33

33 Acknowledgements Spectroscopy: Multi-Quantum-Well: Christian Hauswald, Jonas Lähnemann, Carsten Pfüller Martin Wölz Supervision: Raffaella Calarco, Lutz Geelhaar, Henning Riechert FZ Jülich: Toma Stoica and Detlev Grützmacher Tobias Gotschke, Timo Schumann, Roberta Caterino, Eike Schäfer- Nolte, Milena Erenburg, Johannes Ledig, Andreas Waag, Sebastian Geburt, Carsten Ronning, Stefan Kremling, Eli Sutter, Oliver Brandt, Achim Trampert, Luis Artus, Ramon Cuscó Reviewers: Hans Lüth and Ted Masselink 33/33

34 Biased µ-photoluminescence of the processed nanowire LED PL Intensity [a.u.] V +4 V -10 V V>0 V=0 V< wavelength [nm] PL dependence below LED turn-on (< 5 V) is analysed PL shows a weak dependance on applied bias PL emission only reduced by a factor of 2 with -10 V bias Lähnemann et al., PRB 84, (2011) 34/33

35 µ- electroluminescence as a function of current 580 peak position [nm] LED turn-on integrated EL [a.u.] Polar semiconductors Quantum confined Stark effect current [ma] Shift of emission peak above turn-on indicates screening of an internal field 35/33

36 Growth of Si-doped GaN nanowires Scanning electron microscopy side views 0.3 x cm -3 2 x cm x cm x cm -3 Scanning electron microscopy top views 1 µm 36/33

37 Growth of the active (In,Ga)N region (In,Ga)N quantum wells are inserted in GaN nanowires 100 nm In-situ monitoring of In desorption by QMS X-ray diffraction can be used to determine well thickness partial pressure [10-11 mbar] In Ga time [min] partial pressure [10-11 mbar] In Ga time [min] 37/33

38 Optical properties of the active region Photoluminescence Peak position can be controlled via the substrate temperature norm. intensity [arb. units] InN GaN T S = 475 C T S = 780 C InGaN InGaN T S = 580 C T S = 630 C Raman energy [ev] (In,Ga)N is the source of the luminescence Shift in E 1 (LO) with T S F. Limbach et al. J. Appl. Phys. 109, (2011) 38/33

39 n-i-p vs. p-i-n: µ - Photoluminescence Mechanical removal of the nanowires Deposition on SiO 2 substrate with Au markers Laser spot size 3 µm (20 W/cm²) Also for single wires DAP much more pronounced for type A Shift of the near band edge (NBE) peak in type A => ABE emission Geometric effect can be ruled out W/cm² Norm. intensity Type A Type B Energy [ev] 39/33

40 n-i-p vs. p-i-n: Ensemble Cathodoluminescence CL reproduces results from ensemble PL LO Phonon replica of the DAP emission can be detected Type A Type B GaN NW ref NBE peak emission rather broad compared with PL Slight shift to lower energies for samples of type A 40/33

41 n-i-p vs. p-i-n diodes: Origin of suppressed Mg-incorporation X Polarity flip Determination of the polarity via electron energy loss spectroscopy (EELS) confirmed that all NW are N-polar Incubation time Net time of Mg incorporation is smaller Higher growth rate for GaN NWs at the beginning of growth Mg is distributed in a bigger volume [1] Re-evaporation of Mg adatoms Incorporation of Mg atoms into the substrate Either in Si or forming Mg x N y or Mg x Si y N z at the surface [1] V. Consonni et al. Phys. Rev. B 85, (2012) 41/33

42 n-i-p vs. p-i-n: Monochromatic CL - Type A Cross sectional CL indicates that DAP emission originates from the top of the wires as intended NBE emission from both top and bottom of the NWs GaN:Mg GaN GaN:Si [ev] Si 42/33

43 n-i-p vs. p-i-n: Monochromatic CL - Type B Origin of the DAP emission can not be determined NBE emission from the top of the NWs dominates GaN:Si GaN GaN:Mg Si 43/33

44 Transmission electron microscope analysis Amorphous SiN x interlayer exists despite AlN deposition Polarity determination via electron energy loss spectroscopy (EELS) N-polarity for both types of samples 1 No significant difference could be detected between types A and B via TEM GaN [0001] AlN Si GaN Si SiN x Si [1] X. Kong, et al., APL 81, 11, 1990 (2002) 44/33

45 InGaN overgrowth of the GaN-NWs combining: PL, Raman & local EDX with TEM and SEM imaging => a schematic of the morphology can be obtained 20 nm 45/33

46 µ-pl on InGaN heterostructures nm 2200 PL Intensity (counts/10sec.) P = 0,15 mw T = 5 K 2nm Wavelength (nm) Growth: 4h GaN followed by 30min InGaN 46/33

47 µ-electroluminescence as a function of current EL Intensity [a.u.] current I: 8.0 ma 7.0 ma 6.0 ma 5.0 ma 4.0 ma 3.0 ma 2.0 ma 1.0 ma 0.5 ma 0.1 ma peak position [nm] LED turn-on integrated EL [a.u.] wavelength [nm] current [ma] Emission centered around 535 nm nm Shift of emission peak above turn-on indicates screening of an internal field 47/33

48 EDX of a InGaN/GaN heterostructure InGaN cap (30min) GaN nanowire (4h) 50 nm Ga In Cu 48/33

49 L-vs-d for self-induced nanowires 49/33

50 GaN-nanowire-based LEDs Kikuchi JJAP 43 (2004) Sofia Uni., Tokyo Sekiguchi APL 96 (2010) Sofia Uni., Tokyo Bavencove PSSA 207 (2010) CEA/LETI Grenoble Guo Nano Let. 10 (2010) Uni. Of Michigan, Ann Arbor Armitage Nanotech. 21 (2010) Panasonic Electric Works, Osaka Lin APL 97 (2010) Tsing-Hua Uni., Taiwan Nguyen Nano Let. 11 (2011) McGill Uni., Montreal 50/33

51 TEM Au Ti Au Ni GaN SiO x 51/33

52 Turn-on behavior on the single wire level 3.8 V N: number of emitting spots [10 6 cm -2 ] bias [V] dn/dv [10 6 cm -2 V -1 ] No significant wire luminescence below 3.5 V Two distinct turn-on voltages can be observed with a separation of 2 V The two species show different colors 52/33

53 NW LED additional characteristics Efficiancy 10 7 M First GaN NW LED integrated EL luminescence (a.u.) slope: 1,6 int. EL / Power [a.u.] forward current [ma] Power (mw) Output power increasing super-linear with current Non-radiative recomb. channels play a role in this region Until now, no droop visible 53/33

54 EBIC after MOSFET fabrication followed by NW LED overgrowth MOSFET fabrication at Uni. Braunschweig, A. Waag 54/33

55 EBIC after MOSFET fabrication followed by NW LED overgrowth MOSFET fabrication at Uni. Braunschweig, A. Waag 55/33