STR Group, Ltd.




  engineering tool for
  LED and laser diode
design and optimization
        October 2008
            ...
GaN total market and important
                                                  optoelectronic sectors
                  ...
Main application areas of
                                 III-nitride LEDs and LDs
   Green                Blue          ...
Challenges in modeling
        advanced light-emitting devices

Complex multi-scale 3D geometry
of state-of-the-art LEDs a...
Hybrid approach to
                                              modeling LED dice
            I-V characteristic,
       ...
Hybrid approach to
                                      modeling LED dice

                      semitransparent electrod...
SimuLED™ – coupled software
                tools for LED modeling

SiLENSe™ – 1D simulator of carrier
  injection and lig...
SiLENSe



SiLENSe – software for
   development and
    optimization of
    LED/laser diode
   heterostructures
         ...
SiLENSe – 1D drift-diffusion
         simulation of LED heterostructure


Band diagrams
Carrier concentrations
Electric fi...
SiLENSe – 1D simulator for
                       LED heterostructures

                                      specificatio...
SiLENSe – 1D simulator for
   LED heterostructures




                 editable database
                    of materials...
SiLENSe – basic equations

Poisson equation                             account of
                                       ...
SiLENSe – basic equations

   Recombination model

             R=R           +R          +R +R
                      SR  ...
SiLENSe – basic equations

Quantum-mechanical analysis of emission spectrum




complex valence
 band structure           ...
SiLENSe – Competitive
                             advantages
Advanced physical models:
                                  ...
SiLENSe




Application
 examples

                    16
Blue MQW LED
                                                                                                             ...
Factors affecting the
                                                                         internal quantum efficiency...
Effect of barrier doping on
                                                                                    operation ...
Experimental identification
                        of most efficient QW




 A. David et al, Appl. Phys. Lett. 92
       ...
LED heterostructure with
                                                    a wide GaN active region
                    ...
Threading dislocation effect
                                                             on IQE of deep-UV LEDs

        ...
Distributed polarization doping
                    in graded-composition alloys
                                         ...
Band diagrams of LDs with
                                                           different EBL designs




           ...
Use of distributed polarization
                                                to improve EBL design

                   ...
IQE rollover caused by
                                                                                Auger recombination...
IQE rollover caused by
                                                                    Auger recombination
External qu...
New structure design accounting
                                              for Auger recombination

                   ...
Hybrid ZnO/AlGaN LED
                                                                 single heterostructure
             ...
Hybrid II-O/III-N LED
                                                                      double heterostructures
      ...
Comparison of performances
                                             of various ZnO-based LEDs
                        ...
SiLENSe




 SiLENSe –
Laser Edition

                     32
Special options for
                           laser characteristics
Combined with the main functionality of the SiLENSe
 ...
Specific features of
                                III-nitride lasers
                                              meta...
375 nm UV LD on sapphire
                          substrate (waveguiding)

                                              ...
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
Modeling of Devices with SimuLED
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Modeling of Devices with SimuLED

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Modeling of Devices with SimuLED

  1. 1. STR Group, Ltd. engineering tool for LED and laser diode design and optimization October 2008 1
  2. 2. GaN total market and important optoelectronic sectors 10 HB LED market ($ billion) OIDA Total GaN market ($ billion) 10 1 1 High-brightness LED market history 0.1 1995 1998 2001 2004 2007 2010 Compilation of Year forecasts from various sources 0.1 Laser diode market ($ billion) 1995 1998 2001 2004 2007 2010 10 Strategies Unlimited Year M. Leszczynski Strategy Analytics 1 up to now, the total GaN market nearly Forecasts from corresponds to the various sources 0.1 market of III-N LEDs 1995 1998 2001 2004 2007 2010 Year 2
  3. 3. Main application areas of III-nitride LEDs and LDs Green Blue Violet UV UV 550-520 nm 470-420 nm 405 nm 365-340 nm 280-250 nm Solid-state Water & air Solid-state Curing and lighting with disinfection lighting by drying of inks, phosphors coatings, and RGB mixing Food steri- adhesives Signs lization Signs Medicine Medicine Traffic lights Traffic lights False banknote Chemical Display Entertainment detection back-lighting catalysis HR optical Automotive lithography Entertainment DVD writing New generation of and playing Projection TV DVD systems Optical data (~300 nm) storage 3
  4. 4. Challenges in modeling advanced light-emitting devices Complex multi-scale 3D geometry of state-of-the-art LEDs and LDs Coupled current-spreading and heat-transfer problems; very non-linear equations Non-ordinary properties of novel III-nitride and II-oxide materials → Huge simulation time and computer resources demanded ! 4
  5. 5. Hybrid approach to modeling LED dice I-V characteristic, 3D ray tracing emission spectrum, series resistance, temperature distribution, external 3D model of light extraction efficiency current spreading efficiency & heat transfer U p −n = Fn − Fp p-n Fn difference neutral neutral junction between the region region Fp region quasi-Fermi levels at the x boundaries of p-n junction current density, IQE, and region z emission spectra versus 1D model of y p-n junction bias carrier transport & light emission 5
  6. 6. Hybrid approach to modeling LED dice semitransparent electrode: p-n junction unipolar 2D current spreading region: conductivity distributed non- J = −σ∇U p-pad linear resistor neutral p-region J z = J z (U p −n ) n-pad z ηint = ηint (J z ) neutral y n-region x Calculated with SiLENSe substrate or specified manually 6
  7. 7. SimuLED™ – coupled software tools for LED modeling SiLENSe™ – 1D simulator of carrier injection and light emission in III-N and II-O LED structures SpeCLED™ – 3D simulator of current spreading and heat transfer in LED dice 90 120 60 RATRO™ – 3D ray-tracing analyzer of 30 150 light propagation and extraction 180 0 in LED dice 330 210 240 300 270 7
  8. 8. SiLENSe SiLENSe – software for development and optimization of LED/laser diode heterostructures 8
  9. 9. SiLENSe – 1D drift-diffusion simulation of LED heterostructure Band diagrams Carrier concentrations Electric filed Radiative and non- radiative recombination Internal emission efficiency Carrier fluxes Energy levels in QWs Emission and gain spectra Editable database of materials properties 9
  10. 10. SiLENSe – 1D simulator for LED heterostructures specification of individual layer parameters: thickness, doping, and composition layer-by-layer Input data LED structure visualization specification 10
  11. 11. SiLENSe – 1D simulator for LED heterostructures editable database of materials properties that are automatically identified from the input layer parameters 11
  12. 12. SiLENSe – basic equations Poisson equation account of distributed ( )( ) polarization dPz0 ∇ ε 33∇ϕ = q N A − N D + n − p − ∗ − + doping in graded- dz composition materials Continuity equations ∇ ⋅ J n − qR = 0 ∇ ⋅ J p + qR = 0 , account of Equations for carrier fluxes Fermi statistics fo J n = µ n n ∇Fn , J p = µ pp ∇Fp degenerate carriers 12
  13. 13. SiLENSe – basic equations Recombination model R=R +R +R +R SR dis A rad Radiative Shockley-Read recombination of Auger non- non-radiative non-equilibrium radiative recombination at carriers recombination point defects non-radiative recombination at threading IQE = R rad /R dislocations 13
  14. 14. SiLENSe – basic equations Quantum-mechanical analysis of emission spectrum complex valence band structure 14
  15. 15. SiLENSe – Competitive advantages Advanced physical models: new Polar/nonpolar/semipolar heterostructures Distributed polarization doping in graded-composition AlInGaN alloys Original model of non-radiative recombination at dislocations Original model of the effect of localized new states in InGaN QWs on IQE of LED structure Easy to learn: it requires ~1-2 days to start simulations after installing the package Fast operation: the simulator allows full analysis of ~5-10 heterostructures a day SiLENSe is helpful not only for device engineers but also by people doing epitaxial growth of LED and LD heterostructures 15
  16. 16. SiLENSe Application examples 16
  17. 17. Blue MQW LED heterostructure n-GaN barrier NDB = 5×1017 – 5×1018 cm-3 UID-In0.13Ga0.87N N Characterization of 12 nm 3 nm (MQW) the structure: structure: S.S. Mamakin et al., p-GaN n-GaN p-Al0.2Ga0.8N Semiconductors 37 NA = 7×1019 cm-3 ND = 2×1018 cm-3 NA = 7×1019 cm-3 (2003) 1107 0.5 µm 4-5 µm 0.1 µm 60 nm Recombination rates Band diagram Carrier concentrations 1021 6 30 10 2 j = 38 A/cm non-radiative Recombination rate (cm s ) Carrier concentration (cm-3) 28 -1 10 1020 5 reconbination -3 26 10 radiative 1019 4 recombination 24 Energy (eV) 10 electrons 18 3 10 22 10 Fn 20 holes 10 1017 2 Fp 18 10 16 1 10 16 10 15 0 10 14 j = 38 A/cm2 10 j = 38 A/cm2 12 14 10 -1 10 600 650 700 750 800 850 900 600 650 700 750 800 850 900 600 650 700 750 800 850 900 Distance (nm) Distance (nm) Distance (nm) 17
  18. 18. Factors affecting the internal quantum efficiency Internal emission efficiency 0 10 8 -2 -1 Nd= 10 cm 10 operation External efficiency temperature experiment (b026) -1 10 -2 10 with ηext= 13 % 17 -3 5x10 cm dislocation 18 -3 1x10 cm density 18 -3 3x10 cm -2 10 -3 18 -3 10 5x10 cm Light emission efficiency 1.0 n-GaN -4 -3 -2 -1 0 1 2 3 PL intensity (arb.units) 10 10 10 10 10 10 10 10 17 -3 n0= 1×10 cm 2 Current density (A/cm ) 0.8 {} 0.6 0.4 16 -3 ∆n = 5×10 cm 17 -3 ∆n = 5×10 cm 0.2 structure 18 -3 ∆n = 5×10 cm MQW barrier design 0.0 4 5 6 7 8 9 10 11 doping 10 10 10 10 10 10 10 10 -2 Dislocation density (cm ) 18
  19. 19. Effect of barrier doping on operation of MQW LEDs 21 21 10 10 only the QW 17 -3 19 -3 1 1 ND= 5x10 cm ND= 2x10 cm 20 20 adjacent to Concentration (cm ) Concentration (cm ) 10 10 3 3 0 0 AlGaN EBL 19 19 10 10 Energy (eV) Energy (eV) -1 electrons -1 electrons gives a major 18 18 10 10 rise to -2 -2 holes holes 17 17 10 10 recombination -3 -3 16 16 10 10 at a high barrier -4 -4 15 15 doping 10 10 460 480 500 520 540 560 460 480 500 520 540 560 Distance (nm) Distance (nm) 19 -3 28 ND= 2x10 cm 28 10 10 Recombination rate Recombination rate 25 25 10 10 nonradiative 22 22 10 10 19 19 10 10 nonradiative radiative 16 16 10 10 17 -3 ND= 5x10 cm radiative 13 13 10 10 460 480 500 520 540 560 460 480 500 520 540 560 Distance (nm) Distance (nm) 19
  20. 20. Experimental identification of most efficient QW A. David et al, Appl. Phys. Lett. 92 Appl. Lett. (2008) 053502 (Phillips Limuleds) Limuleds) On the basis of wavelength-resolved far-field pattern measurements the conclusion was made that only the QW adjacent to p-AlGaN blocking layer emits light effectively 20
  21. 21. LED heterostructure with a wide GaN active region 5 1.8 0.8 Internal quantum efficiency 2 2 j = 26 A/cm 200 nm p-GaN j = 20 A/cm 0.7 1.5 4 EL intensity (a.u.) 200 nm p-AlGaN 0.6 1.2 200 nm n-GaN active region 0.5 3 Energy (eV) Fn 0.9 200 nm n-AlGaN 0.4 GaN 2 0.3 active 0.6 region 0.2 1 4-6 µm n-GaN 0.3 Fp 0.1 d 0 0.0 0.0 8 9 10 10 10 10 -2 Dislocation density (cm ) -1 sapphire substrate 400 600 800 1000 1200 Distance (nm) 0.8 3.5 Internal emission efficiency A.S.Usikov et al, Phys.Stat.Solidi 0.7 External efficiency (%) 3.0 8 -2 (c) 0 (2003) 2265 (TDI, Inc.) Nd = 2x10 cm 0.6 2.5 0.5 2.0 0.4 1.5 The LED structure is grown by HVPE 0.3 9 -2 Nd = 10 cm 1.0 that is much cheaper compared to 0.2 0.5 0.1 conventional MOCVD technique 0.0 0.0 0 5 10 15 20 25 30 2 Current density (A/cm ) 21
  22. 22. Threading dislocation effect on IQE of deep-UV LEDs 10 -2 -1 10 Nd = 10 cm At Nd < 107-108 cm-2, IQE is no -3 External efficiency 10 Internal efficiency longer limited by non-radiative with ηext= 2 % carrier recombination at -2 10 threading dislocation cores -4 10 -3 2 200 x 200 µm device 10 2 -5 10 1 x 1 mm device 0 10 -2 -1 0 1 2 3 4 10 10 10 10 10 10 10 Internal efficiency 2 Current density (A/cm ) -1 10 A.J.Fisher et al, Appl.Phys.Lett. 84 Appl.Phys.Lett. -2 10 (2004) 3394 8 -2 Nd = 10 cm (Sandia Labs) 9 -2 Nd = 10 cm -3 10 10 -2 Nd = 10 cm Wavelength ~ 290 nm -3 -2 -1 0 1 2 3 4 10 10 10 10 10 10 10 10 Output power up to 1.35 mW 2 Current density (A/cm ) Current 300 mA Forward voltage 9.4 V 22
  23. 23. Distributed polarization doping in graded-composition alloys EBL design XAlN graded- nominal: 0.5 composition zero PC constant AlGaN 0.3 composition 0.1 polarization [0001] charge (PC) XAlN GaN dP negative graded-down: ρ=− z 0.5 PC descending dz 0.3 composition 0.1 [0001] Distributed polarization XAlN doping has been proposed, graded-up: positive for the first time, for HEMTs 0.5 ascending PC 0.3 composition D. Jena et al., Phys.Stat.Solidi 0.1 (c) 0 (2003) 2339 [0001] 23
  24. 24. Band diagrams of LDs with different EBL designs Partial current density (A/cm ) improvement of band line-up in 2 1 2 j = 5.3 kA/cm the LD structure and suppression 4 10 0 of electron leakage Energy (eV) electron -1 current -2 3 10 Partial current density (A/cm ) hole current 2 1 2 -3 j = 5.3 kA/cm 4 10 0 -4 2 10 T = 300 K Energy (eV) electron -1 graded-down -5 current 1650 1700 1750 1800 -2 3 10 Partial current density (A/cm ) Distance (nm) hole current 2 1 -3 2 j = 5.3 kA/cm nominal 4 10 0 -4 2 10 T = 300 K Energy (eV) M. Kneissl, et al., -1 -5 electron current APL 82 (2003) 2386 1650 1700 1750 1800 -2 3 10 Distance (nm) hole current -3 graded-up minor effect of -4 2 10 composition T = 300 K -5 grading on band 1650 1700 1750 1800 diagram: a lower Distance (nm) barrier to holes 24
  25. 25. Use of distributed polarization to improve EBL design 0.5 Internal quantum efficiency constant composition 1.0 graded-up Injection efficiency 0.4 graded-down 0.8 9 -2 Nd= 10 cm 0.3 9 -2 Nd= 10 cm 0.6 T = 300 K threshold T = 300 K threshold 0.2 0.4 constant composition 0.1 0.2 graded-up graded-down 0.0 0.0 0 1 2 3 4 5 0 1 2 3 4 5 10 10 10 10 10 10 10 10 10 10 10 10 2 2 Current density (A/cm ) Current density (A/cm ) Graded-down EBL provides a dramatic suppression of the electron leakage in the LD and a high IQE at room temperature. Graded-up EBL affects weakly the injection efficiency and IQE 25
  26. 26. IQE rollover caused by Auger recombination -23 rollover of IQE is predicted 10 InSb Coefficient Ctot (cm s ) , direct for blue SQW LED like that 6 -1 -25 10 CdHgTe indirect fabricated at Nichia GaSb -27 10 InAs 1.2 -29 GaP InGaN InGaAs Internal quantum efficiency 10 GaAs n-Auger p-Auger 1.0 Ge Si InP AlGaAs -31 6H-SiC 10 both n/p 4H-SiC without 4x10-31 0.8 -33 Auger 10 0.6 -35 10 0.0 0.6 1.2 1.8 2.4 3.0 3.6 0.4 Bandgap (eV) 2x10-31 4x10-31 0.2 empirical estimation of 0.0 -3 -1 1 3 5 10 10 10 10 10 the Auger recombination 2 Curent density (A/cm ) coefficient 26
  27. 27. IQE rollover caused by Auger recombination External quantum efficiency 0.6 0.6 Internal quantum efficiency 0.5 0.5 400 nm 0.4 0.4 470 nm 0.3 0.3 428 nm pulsed blue SQW LED 460 nm 0.2 0.2 blue MQW LED 530 nm pulsed 0.1 -31 6 -1 0.1 C = 5x10 cm s a τnr = 50 ns b experiment modeling 0.0 0.0 0 1 2 0 1 2 10 10 10 10 10 10 2 2 Current density (A/cm ) Current density (A/cm ) Close correlation between the measures EQE and IQE predicted for SQW and MQW LED structures with account of Auger recombination in the active region 27
  28. 28. New structure design accounting for Auger recombination 0.4 Internal quantum efficiency 6 QWs 13 nm 0.3 active 2 QWs layer 0.2 8 -2 Nd = 5x10 cm λ = 430 nm six 3 nm QWs 0.1 13 nm active layer λ = 430 nm 0.0 1 10 100 1000 2 Current density (A/cm ) Measurements reported in: N. F. Gardner, in: Simulation results, accounting for et al., APL 91 (2007) 243506 Auger recombination (Phillips Lumileds) Lumileds) 28
  29. 29. Hybrid ZnO/AlGaN LED single heterostructure -1 n-ZnO p-Al0.12Ga0.88N e1 EC -2 e2 7×1017 cm-3 5×1017 cm-3 n= Tunnel p= -3 Energy (eV) 0.8 µm 1.0 µm interface -4 hh1 emission Ya.I.Alivov et al, -5 hh2 Appl.Phys.Lett 83 (2003) 4719 -6 EV -7 I = 1 mA -8 -1 990 995 1000 1005 1010 I = 19 mA T = 315 K Distance (nm) -2 Wavelength (nm) Energy (eV) -3 440 420 400 380 360 Fn -4 experiment Intensity (arb.units) p-AlGaN n-ZnO tunnel -5 emission (350 K) bulk Fp -6 emission -7 975 1000 1025 1050 Distance (nm) 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Type-II band alignment Energy (eV) 29
  30. 30. Hybrid II-O/III-N LED double heterostructures 29 4 2 10 10 Recombination rate (cm s ) Partial current density (A/cm ) -3 -1 2 2 2 j = 475 A/cm j = 475 A/cm radiative 1 n-CdZnO @ 400 K @ 400 K 3 EC 10 26 10 n-CdZnO 0 non-radiative Energy (eV) 2 n-MgZnO 10 -1 p-AlGaN n-ZnO n-MgZnO p-GaN 23 10 -2 1 10 p-GaN p-AlGaN -3 20 10 n-ZnO 0 10 EV -4 [0001] 17 -1 -5 10 10 480 510 540 570 600 480 510 540 570 600 Distance (nm) Distance (nm) hybrid II-O/III-N DHS LEDs provide a high IQE even at elevated operation temperatures. Excellent carrier confinement can be obtained in a CdZnO active region. 30
  31. 31. Comparison of performances of various ZnO-based LEDs 1 10 Internal quantum efficiency CdZnO DHS 2 j = 30 A/cm @ 400 K 0 10 ZnO DHS @ 400 K -1 10 -2 10 80% ZnO/AlGaN SHS 6% @ 350 K -3 p-i-n ZnO 10 @ 300 K -4 10 6 -2 9 -2 8 -2 8 -2 1x10 cm 1x10 cm 2x10 cm 2x10 cm comparative analysis of various ZnO-based LED structures has shown advantage of double-heterostructures to get a high IQE 31
  32. 32. SiLENSe SiLENSe – Laser Edition 32
  33. 33. Special options for laser characteristics Combined with the main functionality of the SiLENSe simulator, new options provide analysis and optimization of III-nitride laser diodes • Computation of the waveguide TE- and TM-modes • Advanced approximation of the refractive index dispersion in nitride materials • Birefringence is taken into account • Computation of the optical gain and losses • Computation of the gain spectrum and optical confinement factor for each quantum well • Optical loss because of the free carriers • Laser characteristics • Threshold current density, differential quantum efficiency 33
  34. 34. Specific features of III-nitride lasers metallic electrode z [0001] has remarkable L metallic contact effect on the waveguide modes III-nitride LDs suffer from insufficient waveguiding heterostructure caused by low refractive index variation with 0 x AlInGaN composition substrate frequently mode leakage in the y substrate occurs in III-nitride lasers 34
  35. 35. 375 nm UV LD on sapphire substrate (waveguiding) 10 3.0 Electric Field Intensity (a.u.) M. Kneissl et al., 9 GaN Glads 2.8 8 2.6 Appl. Phys. Lett. 7 Refractive Index 2.4 TE modes 82 (2003) 2386 6 WG 2.2 m=1 5 2.0 m=8 4 1.8 m=9 3 1.6 2 1.4 1 1.2 0 -1 1.0 -5 -4 -3 -2 -1 0 1 2 µ Thickness (µm) lasing of high-order modes is typical of LDs fabricated on sapphire substrate; a careful optimization of free-carrier losses is therefore required 35

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