by M. Boćkowski Institute of High Pressure Physics PAS, ul. Sokołowska 29/37, Warsaw, Poland

Transcription

1 High Nitrogen Pressure Solution (HNPS) growth of GaN in Multi Feed Seed (MFS) configuration. Highly conductive and semi-insulating crystals. Role of impurities: oxygen, magnesium and beryllium. by M. Boćkowski Institute of High Pressure Physics PAS, ul. Sokołowska 29/37, Warsaw, Poland TopGaN Ltd. ul. Sokołowska 29/37, Warsaw, Poland

2 Outline 1. HNPS method 2. Multi-Feed-Seed (MFS) configuration 3. HNPS-MFS-GaN crystals without an intentional doping 4. HNPS-MFS-GaN crystals grown from Ga:In:N solution 5. HNPS-MFS-GaN:Mg crystals 6. HNPS-MFS-GaN:Be crystals 7. Summary

3 High Nitrogen Pressure Solution (HNPS) growth of GaN crucible N 2 molecules under pressure Dissociative adsorption of N 2 on liquid metal surface 1 GPa 1500 o C T Dissolution and transport to the crystallization zone Ga GaN Spontaneous crystallization Perfect crystallographic quality but too small! T I. Grzegory et al. in Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials, ed. by P. Capper, Wiley&Sons, (2005), 173

4 MFS HNPS growth configuration p=1 GPa dt/dz=5-20 o C/cm t 500 h gallium between seeds b new grown HNPS-GaN 1300 o C 1500 o C T

5 MFS configuration. How it works? N 2 N 2 GaN feed GaN seeds T

6 Seeds by HVPE growth 1. Growth on MOVPE GaN/sapphire 2. Me mask is used 3. Self lift-off procedure 4. 2 inch 1 mm thick free standing HVPE-GaN 5. n=5x10 16 cm -3-2x10 17 cm TDD=5x cm R=1-5 m B. Lucznik et al. Physica Status Solidi C Vol 8, No 7-8

7 Seeds by HVPE growth HVPE-GaN with R=1-5 m -polished mechanically and mechano-chemically to the epi-ready state -cut by a drill pipe to smaller objects

8 H. Teisseyre et.al. Applied Physics Express 5 (2012) HVPE-GaN multistep regrowth Semipolar and nonpolar substrates

9 MFS configuration. Pure gallium between seeds. N 2 N 2 feed (0001) oriented HVPE-GaN seeds T

10 Why the gallium side is grown? stable growth on Ga side unstable growth on N side Stable growth is observed on the Ga side! M. Bockowski et al. Journal of Crystal Growth, vol.246, no.3-4, 2002, pp M. Bockowski et al. Journal of Crystal Growth, vol.310, no.17, 2008, pp

11 Macroscopically flat growth (as grown crystals-ga side up)

12 Nitrogen side Pinholes have flat bottoms!

13 Gallium side

14 Gallium side Mixed growth mode

15 Growth mode depends on supersaturation Supersaturation depends on: -the growth temperatures, dt/dz=5-30 o C/cm -gallium heights between seeds, -the temperature gradient applied. Hillocks R=0.5-1 μm/h Macrosteps and hillocks R=1-2 μm/h Macrosteps R=2-5 μm/h 1320 o C 1500 o C T

16 Growth modes Hillocks-low supersaturation-diffusional transport in the solution Hillocks-corelated with screw and mixed dislocations Etching performed in the liquid eutectic of KOH and NaOH at temperatures ranging from 673 to 723 K.

17 Growth modes Mixed mode-average supersaturation-convection starts in the solution Macrosteps appear

18 Growth modes Macrosteps mode-high supersaturation-strong covection flow

19 Macrosteps mode-step bunching-formation of gallium inclusions

20 Macrosteps Hillocks and mixed growth mode Voids and gallium inclusions No voids, no gallium inclusions Hillocks or mixed growth modes are preferred!

21 HNPS-MFS-GaN substrates

22 Substrates for laser diodes 1. Laser diodes based on HNPS-MFS-GaN have been already demonstrated. U th = V j th =2.5 ka/cm 2 P. Perlin

23 Substrates for laser diodes substrates 2. HNPS-MFS-GaN crystals are used for preparing undulated (locally controlled miscut). M. Sarzynski

24 Optical power, mw Intensity, arb. unit Substrates for laser diodes I th =4-6 ka/cm 2 U th =5.5 V Chip A Electric current, ma A deg B deg Chip B Chips B Chips B M. Sarzynski et al. APPLIED PHYSICS EXPRESS Volume: 5 Issue: 2 : FEB 2012 Chips A Wavelength, nm Chips A

25 8 Free carrier concentration. Van der Pauw/Hall measurements free carrier concentration x cm -3 7 Oxygen concentration by SIMS measurements 8x10 19 cm x10 19 cm -3 3x10 19 cm -3 6x10 19 cm -3 6x10 19 cm E. Litwin-Staszewska, SIMS by R. Jakieła (IF PAN) M. Bockowski et al. Journal of Crystal Growth 350 (2012) 5 10 growth temperature o C

26 Concentration [ at/cm 3 ] Concentration [ at/cm 3 ] SIMS measurements GaN grown at 1380 o C GaN grown at 1430 o C H C O Si H C O Si Depth [ m ] Depth [ m ] SIMS by R. Jakieła (IF PAN)

27 Free carrier concentration. Van der Pauw/Hall measurements free carrier concentration x cm growth from Ga:In:N solution growth temperature o C E. Litwin-Staszewska

28 Concentration [ at/cm 3 ] SIMS Signal [ c/s ] Concentration [ at/cm 3 ] SIMS Signal [ c/s ] Indium in the solution. SIMS analysis No standard for indium-relative measurements GaN grown without In in the o C right axis Al In GaN grown with In in the o C right axis Al In left axis 10 1 H O Si Mg Zn Depth [ m ] The same oxygen 10 level!!! left axis H 10 1 O Si 0 Mg Zn Depth [ m ] SIMS by R. Jakieła (IF PAN)

29 Intensity of CL [a.u.] Indium in the solution. CL analysis K ,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6 3,8 Energy [ev] CL by A. Reszka and G. Teisseyre (IF PAN)

30 Oxygen and nitrogen vacancies? 1. Indium atoms are in the solution; 2. Indium atoms are in the crystals; 3. No InN or InGaN phases in the crystals 4. Oxygen concentration does not change; 5. Free carrier concentration increases. V N O In V Ga Ga N

31 X-ray diffraction reflexion 002; beam dimension: 3x10 mm 2 FWHM FWHM FWHM FWHM R R R R HVPE HVPE/ HNPS (after regrowth) HVPE HVPE/ HNPS (after regrowth) HNPS HNPS-GaN HNPS HNPS [arcsec] [arcsec] [arcsec] [arcsec] [m] [m] [m] [m] X X X 1, X 432 X X X X X X 20 M. Bockowski et al. Journal of Crystal Growth 350 (2012) 5 10

32 Time evolution of the growing crystal a HNPS Å a HVPE Å Δε = (a HNPS -a HVPE )/a HVPE h d HNPS compressive strain HVPE tensile strain B. Lucznik/T.W Clayne Encyclopedia of Material Science and Technology ; Elsevier 2001

33 intensity Seeds quality requirements If a seed (HVPE-GaN) is strained elastically it can be used for further successful growth. 1,6x10 7 FWHM,002 = ,4x10 7 beam dimension: 3x10 mm 2 1,2x10 7 1,0x10 7 8,0x10 6 6,0x10 6 4,0x10 6 2,0x10 6 0,0 16,4 16,6 16,8 17,0 17,2 17,4 17,6 w (deg)

34 Intensity [counts] Seeds quality requirements If a seed (HVPE-GaN) is composed by grains or it is plastically strained, it cannot be used for further successful growth a 17,2 17,3 17,4 17,5 17,6 17,7 17,8 17,9 18,0 [deg]

35 Dislocation densities Etching performed in the liquid eutectic of KOH and NaOH at temperatures ranging from 673 to 723 K. TDD = 10 6 cm -2

36 Multi feed seed GaN:Mg feed (000-1) oriented HVPE-GaN or HNPS-GaN Ga:Mg N Ga Ga:Mg between seeds I. Grzegory et al. Journal of Crystal Growth 350 (2012) 50 55

37 Why the nitrogen side is grown? stable growth on N side unstable growth on Ga side Polarity of the GaN seed surface for stable growth is determined and controlled by the Ga solution and its impurities!

38 Concentration [ at/cm 3 ] HNPS-MFS-GaN:Mg H C O Si Mg Depth [ m ] SIMS by R. Jakieła (IF PAN)

39 ( cm) HNPS-MFS-GaN:Mg room temperature Ea=757meV 0,0005 0,0010 0,0015 0,0020 0,0025 0,0030 0,0035 1/T (K -1 ) E. Litwin-Staszewska

40 HNPS-MFS-GaN:Mg Near interface region is decorated by MgO. TEM by J.Smalc-Koziorowska

41 HNPS-MFS-GaN:Mg The MgO crystallites are epitaxially overgrown by GaN. TEM by J.Smalc-Koziorowska

42 HNPS-MFS-GaN:Mg N a hnps Å a hvpe Å Ga Ga R R HVPE HNPS -1,2 m +1,5 m TDD- 5x cm -2-1,5 m +2 m -4 m +5 m

43 HNPS-MFS-GaN:Mg Surface preparation 100 μm

44 Mobility (cm 2 /Vs) n 2DEG (cm -2 ) HNPS-MFS-GaN:Mg 2D GaN/AlGaN structures on HNPS-MFS-GaN:Mg P1708 HEMT 6x x10 12 GaN/AlGaN on GaN bulk crystals 295K 2100 cm 2 /Vs n 2DEG =5x10 12 cm -2 3 nm GaN 21 nm AlGaN 1 um GaN MBE-222 (Mg) na TG-1296 {M115} 2x Temperature (K) C. Skierbiszewski

45 Intensity [arb.units] GaN:Be What for? GaN:Be GaN:Mg Energy [ev] T. Suski et al. Journal of Crystal Growth 230 (2001)

46 GaN:Be What for? Emission intensity is only slightly lower than that of the Lumileds conversion cap! Measurments: Michael Fraunhofer IAF Emission after illumination by InGaN (405 nm) laser H. Teisseyre ISSLED2012, July 2012, Berlin, Germany

47 GaN:Be How to prepare Ga:Be solution? Homogeneization of Ga:Be solution in Ar 2 Be + O 2 2 BeO 3 Be+ N 2 Be 3 N 2 Films on the Ga surface Ga:Be substrate T

48 GaN:Be Spontaneously grown GaN crystals verify if the solution was well prepared

49 GaN:Be non-polar and semi-polar N-side; Ga-side Polarity of the GaN seed surface for stable growth is determined and controlled by the Ga solution and its impurities!

50 GaN:Be? Problems: 1. Back etching (wetting) 2. Surface passivation 3. Polarity? 4.???

51 Summary 1. HNPS-MFS configuration involves the conversion of free-standing HVPE-grown GaN crystals to free-standing HNPS-GaN, which has with a much higher quality than the seed material; 2. HNPS-MFS configuration allows obtaining stable and macroscopically flat growth of the HNPS-GaN; hillocks or mixed growth modes are preferred; 3. Polarity of the HVPE-GaN seed surface is determined and controlled by the Ga solution and its impurities; 4. Free standing HNPS-GaN crystals can be strongly n-type (GaN:0 or V N ) or semiinsulating (GaN:Mg; GaN:Be); 5. faster growth rate is needed thus some changes of Ga solution properties should be carried out.

52 People IHHP PAS: I. Grzegory, S. Porowski, M. Wróblewski, P. Kwiatkowski, K. Jasik, B.Lucznik, B. Pastuszka, T.Sochacki, G. Godlewski, W. Wawer, G. Kamler, M. Kryśko, B. Sadovyi, E. Litwin-Staszewska, J.Smalc-Koziorowska, G. Nowak, M. Sarzynski, S. Krukowski, C. Skierbiszewski, I.Dzięcielewski, P. Strak TopGaN Ltd.: M. Amilusik, A. Sidor, J. Pawlowska, B. Lucznik, T. Sochacki, J. Smalc-Koziorowska, M.Sarzynski, C. Skierbiszewski IF PAN: A. Reszka, H. Teisseyre, R. Jakieła,

53 This research has been supported by the European Union within European Regional Development Fund, through grants: 1. Innovative Economy (POIG /08); 2. Innovative Economy (POIG /11); and through Polish National Science Centre Grant (DEC-2011/03/B/ST3/02647).