Quantum Well and Quantum Dot Intermixing for Optoelectronic Device - - PowerPoint PPT Presentation

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Quantum Well and Quantum Dot Intermixing for Optoelectronic Device - - PowerPoint PPT Presentation

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Quantum Well and Quantum Dot Intermixing for Optoelectronic Device Integration Chennupati Jagadish Australian National University Research School of Physical Sciences and Engineering, Canberra, ACT 0200 AUSTRALIA c.jagadish@ieee.org

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SLIDE 1

Quantum Well and Quantum Dot Intermixing for Optoelectronic Device Integration

Chennupati Jagadish Australian National University Research School of Physical Sciences and Engineering, Canberra, ACT 0200 AUSTRALIA c.jagadish@ieee.org www.rsphysse.anu.edu.au/eme

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SLIDE 2

Overview

  • Introduction
  • Methods of Intermixing
  • Quantum Wells
  • Ion Implantation Induced Interdiffusion

GaAs/AlGaAs, InGaAs/AlGaAs, InP/InGaAs QWs

  • Lasers, Photodetectors
  • Impurity Free Interdiffusion

GaAs/AlGaAs, InGaAs/AlGaAs, InGaAsN/GaAs QWs

  • Integrated Waveguide-Laser
  • Quantum Dots
  • Suppression of Interdiffusion
  • Implantation Induced Interdiffusion
  • Summary
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SLIDE 3

Photonic I ntegrated Circuits / Optoelectronic I ntegrated Circuits

  • I ntegrated Circuits Show Superior

Performance Over Discrete Devices

  • Multi-functional circuits, e.g. WDM

sources

  • I ntegrated Transceivers
  • Low Cost, Packaging
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SLIDE 4

Photonic I ntegrated Circuits

Different Bandgaps

  • n the same chip
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SLIDE 5

WDM Source

  • ptical

amplifier passive

  • ptical

waveguides

multi

  • wavelength

laser diodes

Optical output (to optical fibre)

dielectric passivation implant isolation

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SLIDE 6

Quantum Well Intermixing

  • Diffusion of In and Ga across interface creates graded region in the

case of GaAs/InGaAs Quantum Wells

  • Changes Bandgap, refractive index, absorption Coefficient

before after

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SLIDE 7

Methods Widely Used for Quantum Well (Dot?) I ntermixing

I mpurity I nduced Disordering, e.g. Zn, Si I mpurity Free I nterdiffusion, e.g. SiO2, SOG I on I mplantation I nduced I nterdiffusion Defects/ I mpurities introduced by these methods enhance atomic interdiffusion Goals: High Selectivity and Low Concentration of Residual Defects while achieving large band gap differences

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SLIDE 8

Widely used in Microelectronics I ndustry Defect Concentration

  • I on Dose, I on Mass, I mplant Temperature,

Dose Rate Defect Depth - I on Energy Selective I on I mplantation using Masks

Why I on I mplantation?

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SLIDE 9

Ion implantation induced quantum well intermixing

Vacancy Interstitial

Point defects:

Ion implantation

Intermixing

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SLIDE 10

Schematic of 4 QW structure (40 keV Proton Defect Profile)

QW1 =1.4 nm QW2=2.3 nm QW3=4.0 nm QW4=8.5 nm

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SLIDE 11

10K Photoluminescence Spectra

H.H. Tan et.al.,

  • Appl. Phys. Lett.

68, 2401 (1996).

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SLIDE 12

Energy Shifts vs. Proton Dose

900oC, 30 sec QW1 =1.4 nm QW2=2.3 nm QW3=4.0 nm QW4=8.5 nm H.H. Tan et.al.,

  • Appl. Phys. Lett.

68, 2401 (1996).

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SLIDE 13

600 650 700 750 800 850 0.86 0.87 0.88 0.89 0.90

InGaAs/InP QW, InP cap InGaAs/InP QW, InGaAs cap

Peak Energy (eV) Annealing Temperature (

  • C)

InP 250nm InP 200nm InGaAs 50nm InGaAs QW InP buffer InP buffer

Thermal Stability of InP/InGaAs QWs with InP and InGaAs

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SLIDE 14

10

12

10

13

10

14

10 20 30 40 50 60 70 80 90 InP capped 25

  • C

200

  • C

Energy Shift (meV) Dose (cm

  • 2)

10

12

10

13

10

14

5 10 15 20 25 30 InGaAs capped 25

  • C

200

  • C

Energy Shift (meV) Dose (cm

  • 2)

Implantation Dose (20 keV P) and Temperature Dependence of Energy Shifts in InP/InGaAs QWs

700oC, 60 sec

  • C. Carmody, J. Appl. Phys. 93, 4468 (2003)
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SLIDE 15

200 250 300 350 400 450

1x10

3

2x10

3

3x10

3

1 x 10

14 cm

  • 2 implanted at 200
  • C

1 x 10

14 cm

  • 2 implanted

at room temperature random InP cap unimplanted Normalised Yield

Channel

200 250 300 350 400 450 1x10

3

2x10

3

3x10

3

1 x 10

14 cm

  • 2 implanted at

room temperature and 200

  • C

random InGaAs cap unimplanted Normalised Yield Channel

Damage Accumulation in InP and InGaAs

InP Cap InGaAs Cap

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SLIDE 16

Tuning the Emission Wavelength of GRINSCH Quantum Well Lasers GaAs/AlGaAs QW Lasers

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SLIDE 17

un-implanted dose A dose B

λ1 λ2 λ3

Tuning the wavelength of QW lasers

p-type contact Oxide isolation QW Substrate n-type contact

dose A < dose B λ1 > λ2 > λ3

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SLIDE 18

GRI NSCH QW Laser and 220 keV Proton Defect Profile

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SLIDE 19

Lasing Spectra and L-I Characteristics of GaAs/AlGaAs QW Lasers

(900oC, 60 sec) H.H. Tan and C. Jagadish, Appl. Phys. Lett. 71, 2680 (1997).

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SLIDE 20

Multi-Step Implantation Scheme for Improved GaAs/AlGaAs QW Laser Performance

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SLIDE 21

Tuning the Detection Wavelength of Quantum Well Infrared Photodetectors (QWIPs)

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SLIDE 22

Quantum Well I nfrared Photodetectors

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SLIDE 23

after λ´

1

λ´2 before λ1

Quantum well intermixing

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SLIDE 24

SI-Substrate 1.3 µm GaAs (Si: 2×1018cm-3)

50 nm Al0.3 Ga0.7As barrier 50 nm Al0.3 Ga0.7As barrier 50 nm Al0.3 Ga0.7As barrier 50 nm Al0.3 Ga0.7As barrier

2 µm GaAs cap (Si: 2×1018cm-3) ×48

4.5 nm GaAs (Si: 2×1018cm-3)

0.5 µm AlAs buffer

QWIP structure Grown by MBE

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SLIDE 25

2 4 6 8 10 12 14 0.0 0.5 1.0 1.5 2.0

Bottom contact+substrate Top contact QWs

Displacement Density (a. u.) Implantation Depth (µm)

Defect distribution profile of 0.9 MeV Protons

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SLIDE 26

Metal contact Multi-QWs Metal contact Bottom contact Substrate

un-implanted dose A dose B

λ1 λ2 λ3 λ1 < λ2 < λ3 dose A < dose B

Top contact

Tuning the wavelength of QWIP

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SLIDE 27

4 6 8 10 12 14 0.0 0.2 0.4 0.6 0.8 1.0 1.2 un-implanted 1×1016 cm-2 2×1016 cm-2 3×1016 cm-2 4×1016 cm-2

Photoresponse (a. u.) Wavelength (µm)

QWIP spectral response

950oC, 30 sec M.B. Johnston et.al,

  • Appl. Phys. Lett.

75, 923 (1999).

  • L. Fu et al,
  • Appl. Phys. Lett.

78, 10 (2001).

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SLIDE 28
  • 3
  • 2
  • 1

1 2 3 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13

3×1016 cm-2 1×1016 cm-2 2×1016 cm-2 reference

Responsivity (mA/W) Bias (V)

Responsivity

  • L. Fu et al, Appl. Phys.
  • Lett. 78, 10 (2001).
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SLIDE 29
  • 6
  • 4
  • 2

2 4 6 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

1e16/RTA/1e16/RTA 2e16/RTA Response (mA/W) Bias (V) reference

Responsivity

  • L. Fu et al, Infrared Phys. & Technol. 42, 171 (2001).

One-step implant-anneal sequence: 0.9 MeV 2×1016 cm-2 / 950ºC 30 s Two-step implant-anneal sequence: 0.9 MeV 1×1016 cm-2 / 950ºC 30 s /0.9 MeV 1×1016 cm-2 / 950ºC 30 s

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SLIDE 30

4 5 6 7 8 9 10 11 12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

∆λ/λ = 15.95% ∆λ/λ = 17.43% un-implanted reference

  • ne-step implant-annealed sample

two-step implant-annealed sample

Photoresponse (a. u.) Wavelength (µm)

Relative spectral response

  • L. Fu et al, Infrared
  • Phys. & Technol.

42, 171 (2001).

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SLIDE 31

I mpurity Free Vacancy Disordering

Silicon dioxide acts as a sink for Ga out-diffusion

(i) Creation of Ga vacancies, (ii) Diffusion of Ga Vacancies

QW Dielectric Film (Silicon Dioxide) Ga Vacancy Ga Atom

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SLIDE 32

Maintains Good Crystal Quality Low Concentration of Residual Defects Low Concentration of Electrically Active Defects Relatively Simple Technique and No Residual I mpurities in the Active Regions

Why I mpurity Free Vacancy Disordering?

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SLIDE 33

Experimental conditions

  • Spin-on glass (un-doped and Ga-doped): 3000

rpm for 30 s, baking at 400°C for 15 min

  • SiO2: Plasma enhanced chemical vapour

deposition (PECVD)

  • TiO2: E-beam evaporation
  • RTA: 700 ºC to 900ºC for 30 s
  • Low temperature photoluminescence
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SLIDE 34

IFVD using doped spin-on layers GaAs/AlGaAs 2 QW structure

un-doped

Wavelength (nm)

P-doped

PL intensity (a. u)

650 675 700 725 750 775

Ga-doped

  • L. Fu et al., Appl. Phys. Lett.

7, 1171 (2002).

  • L. Fu et. Al., Appl. Phys. Lett.

76, 837-839 (2000).

Substrate

SiO2

QWs

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SLIDE 35

IFVD using doped spin-on layers InGaAs/AlGaAs structure

wavelength (nm)

un-doped

860 880 900 920 940 960

Ga-doped

PL Intensity (a. u.)

P-doped

  • L. Fu et. al.,
  • J. Appl. Phys.

92, 3579 (2002)

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SLIDE 36

I ntegration of a Waveguide and a Laser Diode Using I FVD

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SLIDE 37

Lateral waveguiding

P++ GaAs contact layer DQW active layer 1.9 µm 0.1 µm Ridge in the waveguide part Ridge in the gain part waveguide active (gain)

La =0.87 mm (laser diode) Lp = 2.5 mm (waveguide)

  • M. Buda et.al.,
  • J. Electrochem. Soc.

150, G481 (2003).

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SLIDE 38

Quantum Dot Photonic I ntegrated Circuits

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SLIDE 39

Why Quantum Dots?

Three Dimensional carrier confinement Leads to Atom Like Density of States Low Threshold Current Lasers High Quantum Efficiency High Thermal Stability (To) Lasers Lasers operating at 1.3 & 1.55 um on GaAs (VCSELs) Normal I ncidence Operation of QDI Ps

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SLIDE 40

Self Assembled Growth of Quantum Dots

Layer by Layer Growth Lattice matched Systems, e.g. AlGaAs on GaAs Direct I sland Growth Large lattice mismatch Very High I nterfacial Energy, e.g GaN on Saphire Layer by Layer followed by I sland Nucleation Dissimilar Lattice Spacing, Low I nterfacial Energy e.g. I nAs on GaAs

Volmer-Weber Growth Mode Stranski-Krastanow Growth Mode Frank- van der Merwe Growth Mode

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SLIDE 41

Quantum Dot Intermixing

  • Large surface area to volume ratio
  • Non-uniform composition profile
  • Large strain field around the dots
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SLIDE 42

Growth details

  • Aixtron 200/4 MOCVD

reactor

– rotation – IR lamps

  • TMGa, TMIn, AsH3 &

PH3

  • Single layer

In0.5Ga0.5As dots

  • Dot growth ~500-550°C
  • GaAs cap at 650°C

Characterization

  • AFM and PL

GaAs GaAs

300nm 300nm 5- 6ML 50% InGaAs

S-I GaAs Substrate

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SLIDE 43

Amount of Material

  • Increase material:

– Density increases until saturation – Size decreases

6.5ML 5.8ML 5ML 4ML

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SLIDE 44

Temperature - AFM

500°C 520°C 550°C

Height increases with increasing temperature Less incoherent dots with increasing temperature

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SLIDE 45

Experimental Details

  • Samples annealed for 30sec

– Proximity capped RTA – Anneals at 700, 800, 850 and 900°C

Spin on Glass, PECVD SiO2, E-Beam TiO2

  • Photoluminescence

– 10K – Cooled Ge detector – Argon-ion laser at 514.5nm

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SLIDE 46

Thermal stability of single layer QDs

880 920 960 1000 1040 1080 1120 1160 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Wavelength (nm) Intensity (a.u.)

as-grown 750

OC

800

OC

850

OC

900

OC

12K Photoluminescence Spectra

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SLIDE 47

I VFD of single layer QDs Spin on Glass (SOG)

920 960 1000 1040 1080 1120 1160 0.0 0.2 0.4 0.6 0.8 1.0

Wavelength (nm) Intensity (a.u.)

as-grown annealed ref undoped SOG ga SOG ti SOG

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SLIDE 48

Suppression of thermal interdiffusion by TiO2 as function of RTA temperature

20 40 60 80 100 120 140 160 (a)

RTA TiO 2+RTA

PL energy shift (meV)

680 700 720 740 760 780 800 820 840 860 0.4 0.5 0.6 0.7 0.8 0.9 1.0 (b)

FWHM of annealed FWHM of as-grown Annealing temperature (ºC)

Substrate

TiO2

  • L. Fu et.al.,
  • Appl. Phys. Lett.

82, 2613 (2003)

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SLIDE 49

Suppression of interdiffusion using bi- layer SiO2 + TiO2

900 950 1000 1050 1100 1150 1200 0.0 0.2 0.4 0.6 0.8 1.0 1.2

as-grown RTA only SiO2 + RTA SiO2 + TiO2 + RTA

PL intensity (Normalized) Wavelength (nm)

E1 E2

Substrate

SiO2 TiO2 RTA: 850ºC 30 s

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SLIDE 50

Suppression of interdiffusion using bi- layer SiO2 + TiO2 as a function of SiO2 thickness

20 40 60 80 100 120 140

  • 60
  • 40
  • 20

20 40 60 80 100 120

E1 E2

PL energy shifts (meV) Thickness of SiO2 (nm)

  • L. Fu et al, Appl. Phys. Lett. 82, 2613 (2003).
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SLIDE 51

Thermal expansion coefficient

Material α (ºC-1) GaAs 6.86 × 10-6 SiO2 0.52 × 10-6 TiO2 8.19 × 10-6

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SLIDE 52

Thermal stress effect

  • Compressive stress on GaAs

surface ⇒ favourable for VGa diffusion ⇒ enhanced interdiffusion

QDs

Substrate

tensile compressive SiO2

Substrate

compressive tensile TiO2

Tensile stress on GaAs surface ⇒ unfavourable for VGa diffusion ⇒ inhibited interdiffusion Compressive stress on GaAs surface ⇒ favourable for VGa diffusion ⇒ enhanced interdiffusion

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SLIDE 53

Stacked Dots

10-150A 300A

GaP la ye r InGaAs dots GaAs substra te 2000A GaAs c a p

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SLIDE 54

Growth of stacked layers

Top layer of 3- layer stack. With smoothing Density ~4x1010/cm2 Single Layer Density ~4x1010/cm2 Top layer of 3- layer stack. Original conditions Dots smaller than for single layer. Density ~2x1010/cm2 Top layer of 3-layer stack. Low V/III, with GaP layers. Dots slightly flatter. Density ~3x1010/cm2

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SLIDE 55

I FVD of stacked QDs

920 960 1000 1040 1080 1120 1160 0.0 0.2 0.4 0.6 0.8 1.0

Intensity (a.u.) Intensity (a.u.) Wavelength (nm) Stacked layer

0.0 0.2 0.4 0.6 0.8 1.0

Single Layer as-grown

  • ann. ref

SiO2 SiO2/TiO2 TiO2

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SLIDE 56

Implantation

(Single QD Layers)

900 950 1000 1050 1100 1150 1200 0.0 0.2 0.4 0.6 0.8 1.0

Intensity (a.u.) Wavelength (nm)

as-grown annealed 750

OC, 30s

5x10

13H/cm 2

1x10

14H/cm 2

1x10

15H/cm 2

900 950 1000 1050 1100 1150 1200 0.0 0.2 0.4 0.6 0.8 1.0

Wavelength (nm) Intensity (a.u.)

as-grown annealed 1x10

11 As/cm 2

5x10

11 As/cm 2

1x10

12 As/cm 2

5x10

12 As/cm 2

Protons Arsenic Ions

  • P. Lever, Appl. Phys. Lett. 82, 2053 (2003)
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SLIDE 57

Stacked QDs -H implant

1000 1020 1040 1060 1080 1100 1120 1140 1160 1180 1200 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Wavelength (nm) Intensity (a.u.)

as-grown annealed 750

OC, 30s

5x10

13H/cm 2

1x10

14H/cm 2

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SLIDE 58

Energy Shifts – As Ion Dose, Annealing Temperature (Single Layer of QDs)

10

11

10

12

20 40 60 80 100 120 140

Dose (As/cm

2)

Energy Shift (meV)

annealed at 700

OC, 30s

annealed at 750

OC, 30s

annealed at 800

OC, 30s

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SLIDE 59

Energy Shifts vs Implant Temperature (Protons and Arsenic Ions)

20 40 60 80 100 120 140 160 180 200 220 20 40 60 80 100 120 140

Implant Temperature (

OC)

Energy Shift (meV)

5x10

11 As/cm 2

1x10

12 As/cm 2

5x10

14 H/cm 2

1x10

15 H/cm 2

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SLIDE 60

Energy Shift and PL Intensity Vs. Displacement Density

10

19

10

20

10

21

20 40 60 80 100 120 140

Displacements (cm

  • 3)

Energy Shift (meV)

H As

10

19

10

20

10

21

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Displacements (cm

  • 3)

Intensity (norm)

H As

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SLIDE 61

Summary

Quantum Well and Quantum Dot I ntermixing Techniques are promising for Optoelectronic Device I ntegration Understanding defect generation, diffusion and annihilation processes are important for achieving QWI and QDI Dopant diffusion issues need to be taken into consideration for Device Structures such as Lasers and Photodetectors

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SLIDE 62

Acknowledgements

Australian Research Council – Funding

Past and Present Members of Semiconductor Optoelectronics And Nanotechnology Group, ANU (H.H.Tan, L. Fu, P. Lever, M. Buda, P.N.K. Deenapanray, J. Wong-Leung, Q. Gao, C. Carmody, R.M. Cohen,

  • A. Clark, G. Li, M.I . Cohen, S. Yuan, Y. Kim, K. Stewart,
  • P. Gareso, A. Allerman…)

Many Collaborators in Australia (Mike Gal, M.B. Johnston. P.Burke, L.V. Dao, P.Reece, B.Q. Sun, David Cockayne. Zou Jin) and Overseas