Transcript
  • Comparison of the uniformity of thickness and cryst al quality of III-nitride films grown by ammonia source and plasma source MBE

    Y. Cordier 1, M. Portail 1, M. Chmielowska 1, F. Natali 1,2, C. Chaix 2, P. Bouchaib 2

    1 CRHEA-CNRS, rue Bernard Grégory, Sophia Antipolis, 06560 Valbonne, France2 RIBER S.A, 31 rue Casimir Périer, BP 70083, 95873 Bezons Cedex, France

    Complementary information

    Ammonia MBE :

    Ts~800°C (GaN) to 920°C (AlN), nitrogen rich, growth rate limited by

    group III fluxes

    Trapping of ammonia on cryo-panels ���� recovery procedure

    Interest for reducing NH3 consumption

    Plasma assisted MBE: Addon plasma cell (model RFN50/63)

    GaN (Ts~720°C), usually metal rich, more complicated : necessary to

    tune group III fluxes, N2 flow rate and RF power

    AlN (Ts~830°C), metal or nitrogen rich

    GaN and AlN films grown by plasma assisted-MBE and by ammonia-MBE

    to study the influence of the nitrogen source and of the gas flow rate :

    -on the uniformity of thickness

    -on the surface and crystal quality

    AlN grown on Si(111)

    GaN grown on :

    • Si (111) with GaN/AlN buffer layers

    • GaN-on-sapphire templates grown by MOCVD (LUMILOG)

    Introduction

    0,8 1,0 1,2 1,4 1,6 1,8

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    0,60

    Ga-rich conditions (2-3MLs segregating)

    Power (W ) = 550W Power (W ) = 500W Power (W ) = 400W

    Gro

    wth

    rat

    e (µ

    m/h

    )

    N2 flow rate (sccm)

    Trade-off : growth rate – quality ���� P ~ 400-450 W, 1-1.8 sccm, Ts ~ 720 °C

    ■ Mesrine et al . Appl. Phys. Lett. 72 (3) p.350 – 1998).Riber 32 reactor

    � from 200 to 80 sccm : increase of

    the GaN growth rate ; reduction of

    the screening effect of NH3.

    Vg: 0.61 – 0.68 µm/h

    � below 20 sccm : decrease of

    GaN growth rate due to insufficient

    supply of nitrogen.

    Ga : BEP ~ 5E-7 Torr

    NH3 20 sccm : BEP ~ 7E-5 Torr

    ����NH3 cracking efficiency of a few %

    Effect of nitrogen flow rate and RF power.

    Growth using a nitrogen plasma source (Ga-rich growth regime) T > 700°C

    Depending on growth conditions, AFM shows terraces with a mean height of step of 1 molecular monolayer (left)

    and 2 monolayers (right)

    AFM – 1x1 µm²

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    1,1

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    NH3 (sccm)

    Vc

    GaN

    (µm

    /h)

    this study

    Mesrine

    NH3 screening effect

    ‘’N’’ limited growth

    ‘’N’’ rich growth

    NH3 min :

    200 sccm

    NH3 min :

    80 sccm

    NH3 min :

    40 sccm

    NH3 min :

    20 sccm

    below 80 sccm : development of pits related to dislocations

    from 200 to 80 sccm : increase of the roughness.

    growth mode intermediate between

    2D nucleation and step flow

    ⇒ Step height 1 ML (0.25 nm)

    GaN ammonia growth : effect of flow rate GaN plasma assisted growth :

    Thickness uniformity

    XRD results

    AFM 1x1 µm²

    AlN / GaN grown on 4” , 3” and 2” silicon

    Silicon substrate

    AlN Nucleation layer

    GaNBuffer layer

    Advantages:-Contactless -Fast measurements-Tunable probe size ~2-6 mmDrawbacks:-Accuracy decreases when thickness decreasesin the interference regime (necessitates thesimulation of TO mode broadening )Set up bench-IR source : 50-9000cm-1

    -Detector range (DGTS) : 380 – 7500cm-1

    RIBER Compact 21T

    VbVb-Vg

    EF

    Conduction band

    Depletion region : h dh~0

    Low doped

    Highly doped

    The capacitance is almost independent with Vb, Nd-Na

    VbVb-Vg

    EF

    Conduction band

    Depletion region : h dh~0

    Low doped

    Conduction band discontinuityhigh polarization field at the interfaceFermi level pinning by defects

    Mercury probe CV (Hg-CV) Fourier Transform InfraRed spectroscopy (FTIR)

    centre RMS = 1.66 nm

    centre + 25 mmRMS = 1.54 nm

    centre + 40 mm RMS = 1.66 nm

    centreRMS = 0.31 nm

    centre + 30 mm RMS =0.47 nm

    centre + 20 mm RMS = 1.40 nm

    centreRMS = 0.96 nm

    150 nm AlN plasma N-rich on 3’’ Si

    centreRMS = 0.51 nm

    centre + 20 mmRMS = 0.58 nm

    centre + 30 mmRMS = 0.55 nm

    200 nm AlN NH3 130 sccm on 4’’ Si

    centreRMS = 0.12 nm

    centre + 30 mmRMS = 0.12 nm

    centre + 40 mm RMS=0.13 nm

    UniformityInfluence of nitrogen source and flow rate

    Thickness uniformity from Hg-CV Comparison Hg-CV vs FTIR Thickness uniformity from F TIR

    AFM : surface morphology

    centre + 30 mm RMS = 2.90 nm

    150 nm AlN plasma Al-rich on 3’’ Si

    600 nm GaN NH3 200 sccm on 4’’ Si

    600 nm GaN plasma Ga-rich on 3’’ Si

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    NH3 flow rate (sccm)

    FW

    HM

    (a

    rcse

    c)

    0,13 µm AlN NH3: XRD (002), (101)

    AlN FWHM (101)

    AlN FWHM (002)

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    centre c+10mm c+20mm c+30mm c+40mm

    0,6µm GaN NH3 (200 sccm)

    0,6µm GaN NH3 (200 sccm)

    0,5µm GaN plasma (Ga-rich)

    1µm GaN NH3 (200 sccm)

    2,6µm GaN NH3 (200 sccm)

    GaN (302) XRD

    FW

    HM

    (a

    rcse

    c)

    Position (mm)

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    centre c+10mm c+20mm c+30mm c+40mm

    0,6µm GaN NH3 (200 sccm)

    0,6µm GaN NH3 (200 sccm)

    0,5µm GaN plasma (Ga-rich)

    1µm GaN NH3 (200 sccm)

    2,6µm GaN NH3 (200 sccm)

    GaN (002) XRD

    FW

    HM

    (a

    rcse

    c)

    Position (mm)

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    0,20

    0,25

    -50 -40 -30 -20 -10 0 10 20 30 40 50

    h A

    lN (

    µm)

    NH

    3 M

    BE

    position (mm)

    NH3 10 sccm

    NH3 130 sccm

    NH3 200 sccm

    σ = 1,9-2 % over 50 mm σ = 2,6-3,1 % over 60 mm

    σ = 1,9 % over 60 mm σ = 5 % over 80 mm

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    -50 -40 -30 -20 -10 0 10 20 30 40 50

    h G

    aN &

    AlN

    (µm

    ) N

    H3

    MB

    E

    position (mm)

    AlN

    GaN

    σ = 1 % over 60 mm σ = 3 % over 80 mm

    σ = 0,9 % over 50 mm σ = 1,2 % over 60 mm NH3 200 sccm

    NH3 130 sccm

    Continuous lines are data from Hg-CV

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    0 10 20 30 40 50

    h A

    lN (

    µm)

    RF

    vs

    NH

    3

    position (mm)

    AlN NH3

    AlN Al-rich RF N2 = 0,4 sccmAlN N-rich RF

    N2 = 2 sccm

    σ = 2,8 % over 25 mm σ = 3,7 % over 30 mm

    σ = 2,7 % over 25 mm σ = 4,0 % over 30 mm

    σ = 1,5 % over 25 mm σ = 3,2 % over 30 mm

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    h G

    aN (

    µm)

    RF

    vs

    NH

    3

    position (mm)

    GaN NH3

    GaN RF N2=1,8 sccm

    σ = 1,5 % over 30 mm σ = 2,7 % over 40 mm

    σ = 1,4 % over 25 mm σ = 1,9 % over 30 mm

    σ = 2,2 % over 25 mm σ = 3,4 % over 30 mm

    -Influence of nitrogen precursor and its flow rate on the quality and the residual doping in GaN grown by molecular beam epitaxy, Y.Cordier, F.Natali, M.Chmielowska, M.Leroux, C.Chaix, P.Bouchaib, Physica Status Solidi C 9, 523–526 (2012).

    -Advances in quality and uniformity of (Al,Ga)N/GaN quantum wells grown by molecular beam epitaxy with plasma source, F.Natali, Y.Cordier, C. Chaix, P.Bouchaib, Journal of Crystal Growth (311) 2029–2032 (2009).

    -Signature of monolayer and bilayer fluctuations in the width of (Al,Ga)N/GaN quantum wells, F.Natali, Y.Cordier, J.Massies, S.Vezian, B.Damilano, M.Leroux, Physical Review B 79, 035328 (2009).

    -Developments for the production of high quality and high uniformity AlGaN/GaN heterostructures by Ammonia MBE, Y.Cordier, F.Semond, J.Massies, M.Leroux, P.Lorenzini, C.Chaix, Journal of Crystal Growth (301/302) 434-436 (2007).

    -Quality and uniformity assessment of AlGaN/GaN Quantum Wells and HEMT heterostructures grown by molecular beam epitaxy with ammonia source, Y.Cordier, F.Pruvost, F.Semond, J.Massies, M.Leroux, P.Lorenzini, C.Chaix, Physica Status Solidi C 3, 2325-2328 (2006).

    0

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    FWHM 002

    FWHM 101

    FWHM 103

    FW

    HM

    (a

    rcse

    c)

    AlN RF-MBE : XRD (002), (101), (103)

    0,16µm plasma

    (N-rich)

    0,15µm plasma

    (N-rich)*

    0,15µm plasma

    (Al-rich)*

    * : with 40 nm AlN NH3 nucleation layer

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    position (mm)

    h (

    µm)

    AlN

    GaN

    centre + 15 mm RMS = 0.33 nm

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    centre c+10mm c+20mm c+30mm c+40mm

    0,16µm plasma (N-rich)

    0,15µm plasma (Al-rich)

    0,15µm plasma (N-rich)

    0,13µm NH3 (10 sccm)

    0,16µm NH3 (130 sccm)

    0,2µm NH3 (130 sccm)

    0,2µm NH3 (130 sccm)

    AlN (002) XRD

    FW

    HM

    (a

    rcse

    c)

    Position (mm)

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    14000

    centre c+10mm c+20mm c+30mm c+40mm

    0,16µm plasma (N-rich)

    0,15µm plasma (Al-rich)

    0,15µm plasma (N-rich)

    0,13µm NH3 (10 sccm)

    0,16µm NH3 (130 sccm)

    0,2µm NH3 (130 sccm)

    0,2µm NH3 (130 sccm)

    AlN (101) XRD

    FW

    HM

    (a

    rcse

    c)

    Position (mm)


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