Long Wavelength Metamorphic InGaAs Detectors on GaAs Substrates I. - - PowerPoint PPT Presentation

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Long Wavelength Metamorphic InGaAs Detectors on GaAs Substrates I. - - PowerPoint PPT Presentation

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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Long Wavelength Metamorphic InGaAs Detectors on GaAs Substrates I. Adesida, J. H. Jang, J. W. Bae, S. Kim Micro and Nanotechnology Laboratory Department of Electrical and

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SLIDE 1

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Long Wavelength Metamorphic InGaAs Detectors on GaAs Substrates

  • I. Adesida, J. H. Jang, J. W. Bae, S. Kim

Micro and Nanotechnology Laboratory Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign

  • W. E. Hoke

Raytheon RF Components

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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Outline

  • Metamorphic Photodiodes

– Metamorphic Device Technology – Double Heterojunction P-i-I-N Photodiodes

  • Heterostructure design
  • Fabrication processes

– Wet etch process and dry etch process

  • Device performance

– Monolithic Integration with HEMTs (High Electron Mobility Transistors)

  • Summary
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SLIDE 3

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Device Technologies for Optoelectronic Receivers

  • Long Wavelength Photodiodes

In0.53Ga0.47As Lattice Matched to InP

  • Electronic Devices
  • InGaAs/InAlAs HEMTs on InP
  • InGaAs/InP HBTs on InP
  • InGaAs/AlGaAs PHEMTs on GaAs
  • GaAs/AlGaAs HBTs on GaAs
  • SiGe HBTs on Si

1.55 μm

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SLIDE 4

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

What is Metamorphic Technology ?

Lattice Constant ( )

5.4 5.6 5.8 6.0 6.2

Bandgap (eV)

0.0 0.5 1.0 1.5 2.0 2.5 AlAs GaAs InAs InP InxAl1-xAs In1-x-yAlxGayAs Å InxGa1-xAs Δa=0.2155 Å

Metamorphic buffer : lattice-constant transformer from GaAs to InP

Opto-electronic Devices InP Substrates GaAs Substrates Metamorphic Buffer Opto-electronic Devices

Metamorphic In1-x-yAlxGayAs

PDs or HEMTs (Device Heterostructure) GaAs Substrate Ga In Al As

  • J. H. Jang et. al. ECS conference ‘2002 (invited paper)
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Metamorphic Growth by Molecular Beam Epitaxy

AlInAs 53% InGaAs AlInAs Buffer

Linearly Graded InGaAlAs M-Buffer (1.5 μm-thick)

PDs or HEMTs (Device Heterostructure) GaAs Substrate Ga In Al As

In0.52 Al0.48 As Buffer GaAs Substrate Cross-Sectional TEM of Device Heterostructure

  • W. E. Hoke, J. H. Jang et. al. GaAs Mantech ‘2001 (invited paper)
  • W. E. Hoke, J. H. Jang et. al. JVST B. July 2001 pp. 1505-1508
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Advantages of Metamorphic Devices

  • Starting Material Costs for 4-inch Substrates

InP : $1350 /cm2 GaAs : $370 / cm2

  • Large Wafer Sizes

InP : 4-inch Production GaAs : 6-inch Production

  • Mechanical Robustness

Easier Handling/Better yield

  • Mature Processing Technology for GaAs

e.g. Back-side Via Etching for MMIC Process Low Cost!! Manufacturing

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SLIDE 7

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Double Heterojunction Photodiodes

  • High Quantum Efficiency

Reduced Carrier Loss due to Surface Recombination

  • Potential for High Bandwidth

No Diffusion Current at the Anode or Cathode Drift Current dominates the Carrier Transport Advantages of DH Photodiodes

  • Parasitic Series Resistance at the Heterointerface

Bandwidth Degradation

  • Carrier Accumulation at the Heterointerface

Space Charge Field Electric Field Screening Effect Bandwidth Degradation Potential Problems of DH Photodiodes

p i N P i N p i n

Homojunction Single heterojunction Double heterojunction

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SLIDE 8

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Layer Structure of Metamorphic DH Photodiodes

Chirped superlattice graded bandgap layer Transparent anode Transparent cathode Highly doped cap Photo- absorption Transparent drift region Linearly graded Metamorphic buffer layer Quaternary matching layer

p+ InGaAs Be : 4×1019cm-3 P+ InAlAs Be : 5×1018cm-3 P+ InGaAlAs Be : 5×1018cm-3 i InGaAs Undoped InAlAs/InGaAs Undoped I InAlAs Undoped N+ InAlAs Si : 5×1018cm-3 Linearly Graded InGaAlAs

  • S. I. GaAs Substrate
  • J. H. Jang et. al. Electronics Lett. May 2001, pp.707-708
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Large Bandgap Drift Region

InAlAs Drift Layer InGaAs Absorption

Anode Cathode

Electron Transit Time << Hole Transit Time Transit-Time Limited Bandwidth : Determined by Hole Transit Time Adding a Drift Layer at the Cathode Side Reducing Diode Capacitance w/o Sacrificing Transit-Time Limited Bandwidth

Electric Field (kV/cm)

20 40 60 80 100

Drift Velocity (106 cm/s)

5 10 15 20

Electron Hole

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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Energy Band Diagram

Distance from Top Surface (μm)

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Electron Energy (eV)

  • 8
  • 6
  • 4
  • 2

2

0.97 0.98 0.99 1.00 1.01

  • 5.5
  • 5.0
  • 4.5
  • 4.0
  • 3.5

1 2 3 4 5 6 7

p+InGaAs

1

P+InAlAs

2

P+InGaAlAs

3

i-InGaAs

4

SL-GBL

5

I-InAlAs

6

N+-InAlAs

7

Only 0.1 eV Potential Barrier at InGaAs/InAlAs Heterojunction Chirped Superlattice InAlAs/InGaAs Graded Bandgap Layer (SL-GBL) InGaAlAs Quaternary Matching Layer

  • As

Ga In As Al In for x x x E

x x g −

+ + =

1 47 . 53 . 48 . 52 . 2

) ( ) ( 20 . 49 . 76 . ) ( m E hc eV E x

g g g

μ λ 31 . 1 , 95 . ) 34 . ( 0.34, For = = = =

  • J. H. Jang et. al. J. Lightwave Technol. 2002 pp. 507-514
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication Procedure (Wet etch process)

Air-Bridge : 1.8 μm Au N-Ohmic contact Mesa & Undercut etching Passivation : Polyimide AR coating : SiNx P-Ohmic contact Ti/Pt/Au (Unalloyed) Contact resistance < 0.2 Ω-mm AuGe/Ni/Au (Alloyed) Contact resistance < 0.2 Ω-mm Reduce parasitic capacitances SiNx completes AR coating

  • n InAlAs/InGaAlAs

Low dark current Isolation & Low junction capacitance

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SLIDE 12

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication Procedure (Dry etch process)

Air-Bridge : 1.8 μm Au N-Ohmic contact N-mesa etching Passivation : Polyimide AR coating : SiNx P-mesa etching SiO2 mask Cl2/Ar/H2, ICP-RIE AuGe/Ni/Au (Alloyed) Contact resistance < 0.2 Ω-mm Reduce parasitic capacitances SiNx completes AR coating

  • n InAlAs/InGaAlAs

Low dark current P-Ohmic contact Ti/Pt/Au (Unalloyed) Contact resistance < 0.2 Ω-mm SiO2 mask Cl2/N2, ICP-RIE

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SLIDE 13

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication (Wet Etch Process)

P-mesa & undercut etching

Ti/Pt/Au p-Ohmic Metal P+InAlAs/InGaAlAs i-InGaAs (Absorption) I-InAlAs (Drift)

Various mixture of citric acid/H2O2 for selective or non-selective etching Undercut etching of i-InGaAs layer reduce junction capacitance

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SLIDE 14

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication (Dry Etch Process)

P-mesa etching (InGaAs/InAlAs) Chemistry : Cl2/H2/Ar Bias voltage : -150 V

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SLIDE 15

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication (Dry Etch Process)

N-mesa etching (InAlAs) Chemistry : Cl2/N2 Bias voltage : -150 V InP InGaAs InAlAs

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SLIDE 16

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabricated Photodiodes

SiNx AR Coated Optical Window Polyimide Passivation Airbridge

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SLIDE 17

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Dark currents of various M-PDs and LM-PDs

  • J. H. Jang et. al. J. Lightwave Technol. 2002 pp. 507-514

Area of Photodiodes (μm2)

102 103 104

Dark Current (A)

10-10 10-9 10-8 10-7 10-6

LG LM SG SG LG LM

Linearly Graded M-buffer Step Graded M-buffer Lattice Matched On InP M-PDs : Metamorphic Photodiodes on GaAs, LM-PDs : Lattice Matched Photodiodes on InP

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SLIDE 18

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Dark Current Characteristics

  • Smooth Curve

No Charge Accumulation Effect Chirped Superlattice Graded Bandgap Layer, and InGaAlAs Matching layer

Area of devices (μm 2)

102 103 104

Dark current (A)

10-9 10-8 10-7 Passivated with SiN x Unpassivated Passivated with Polyimide

  • Effect of Passivation Technique on Dark Current of Photodiodes

High Quality Buffer & Fabrication Process

  • J. H. Jang et. al. J. Lightwave Technol. 2002 pp. 507-514
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SLIDE 19

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

RF Characteristics of Photodiodes

38 GHz Normalized Frequency Response Bias Dependent Bandwidths

Increased Depletion Widths, Decreased Electron Velocity in InGaAs

P-i-I-N Photodiode with 10 μm Optical Window

  • J. H. Jang et. al. Photon. Technol. Lett., 2001 pp. 1097-1099
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Comparison between P-i-I-N and P-i-N PDs

Transit time limited BW : RC time limited BW

Increased Bandwidth I-InAlAs Drift Region Reduced Capacitance Increased Fiber Alignment Tolerance

  • J. H. Jang et. al. Photon. Technol. Lett., 2001 pp. 1097-1099
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Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

DC Photoresponses

Bias Voltage (V)

2 4 6 8 10

Photocurrent (mA)

10-2 10-1 100 101

Pinc = 5.25 mW

Popt from laser : -11 dBm ~ 7 dBm

Input Optical Power (dBm)

  • 10
  • 5

5

Photocurrent (mA)

10-1 100 101 Responsivity (A/W) 0.4 0.5 0.6 0.7 0.8

Photocurrent of P-i-N Photocurrent of P-i-I-N Responsivity of P-i-N Responsivity of P-i-I-N

Responsivities ~ 0.60 A/W SiNx Coating & InAlAs/InGaAlAs Optical Matching Layer

  • J. H. Jang et. al. Photon. Technol. Lett., 2001 pp. 1097-1099
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SLIDE 22

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Nonlinear Characteristics of Photodiodes

Incident Optical Power (dBm)

  • 2

2 4 6 8 10

Output RF Power (dBm)

  • 60
  • 55
  • 50
  • 45
  • 40
  • 35
  • 30

Normalized RF Responsivity

  • 3
  • 2
  • 1

1 2 3 f = 30 GHz

  • 2 V
  • 3 V
  • 4 V
  • 5 V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Electron density (1016/cm3)

0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5

Anode Cathode

(a) Jph=8.50 kA/cm2 Jph=17.0 kA/cm2 Jph=25.5 kA/cm2 (b)

Position (μm)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Electric Field (105 V/cm)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Jph=8.50 kA/cm2 Jph=17.0 kA/cm2 Jph=25.5 kA/cm2

Charge Distribution in Depletion Region Total Electric Field in Depletion Region

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SLIDE 23

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

High Speed Photodiodes with BW > 60 GHz

p+ InGaAs Be : 4×1019cm-3 P+ InAlAs Be : 5×1018cm-3 P+ InGaAlAs (x) Be : 5×1018cm-3 i InGaAs (y) Undoped InAlAs/InGaAs Undoped I InAlAs Undoped N+ InAlAs Si : 5×1018cm-3 Linearly Graded InGaAlAs

  • S. I. GaAs Substrate
  • Photo-absorption Layer : x=0.7 0.5 μm

Scaled down to achieve higher speed Reduced responsivity due to the trade-off between BW and QE

  • Quaternary Matching Layer

y = 0.1 μm y = 0.3 μm Thickness was increased to reduce the anode ohmic contact resistance

Reverse Bias Voltage (V)

5 10 15

Dark Current (A)

10-10 10-9 10-8 10-7 10-6 10-5

0.6 nA @ 2 V 0.8 nA @ 3 V 1.3 nA @ 5 V 6.2 nA @ 10 V

Reverse Bias Voltage (V)

2 4 6 8 10

Photocurrent (A)

10-5 10-4 10-3 10-2 8.82 mW

  • J. H. Jang et. al. Photon. Technol. Lett., Feb. 2003
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SLIDE 24

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Wavelength Dependent Characteristics

Reverse Bias Voltage (V)

0.0 0.5 1.0

  • 3 dB Bandwidth

10 20 30 40 50 60

High Speed at Low Bias

Photo-Absorption @ i-InGaAs : 0.850, 1.33, 1.55 μm @ I-InAlAs : 0.850 μm Bandwidth and Responsivity 62 GHz, 0.40 A/W @ 1.55 μm 56 GHz, 0.38 A/W @ 1.33 μm 43 GHz, 0.43 A/W @ 0.85 μm

Frequency (GHz)

1 10 100

Relative Frequency Response (dB)

  • 6
  • 3

f-3 dB=61 GHz

  • J. H. Jang et. al. Photon. Technol. Lett., Feb. 2003 accepted
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SLIDE 25

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Monolithic Integration of Photodiodes and HEMTs

Integration of Metamorphic Photodiodes and HEMTs on GaAs

Metamorphic Buffer Layer GaAs Substrate HEMTs layer HEMTs Photodiode

Regrown PD & HEMTs PD on top of HEMTs Shared PD & HBTs PD on HBTs, or HBTs on PD

  • I. Adesida et. al. Optoelectronic Receiver in Encyclopedia of Optical Engineering 2003
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SLIDE 26

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Heterostructures for OEIC

300 Å p + In0.53Ga0.47As Be : Doped p = 1 × 1020 cm-3 2520 Å p + In0.52Al0.48As Be : Doped p = 5 × 1018 cm-3 0.7 μm i - In0.53Ga0.47As Undoped 340 Å In0.52Al0.48As /In0.53Ga0.47As Chirped SL 3000 Å N+ InAlAs Si : Doped N > 1 × 1019 cm-3 80 Å n+ In0.53Ga0.47As Si : Doped n = 5 × 1018 cm-3 140 Å i - In0.52Al0.48As Undoped Si : Delta Doping Plane 40 Å i - In0.52Al0.48As Undoped 200 Å i - In0.53Ga0.47As Undoped 3000 Å i - In0.52Al0.48As Undoped 1.5 μm Linearly Graded InGaAlAs Metamorphic Buffer Layer

S.I. GaAs Substrate

HEMTs PIN

Sheet charge density : n = 2.08 × 1012 cm-2, Mobility : 10,070 cm2/V·s

  • J. H. Jang et al. GaAs IC Symposium 2002 pp. 55-58
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SLIDE 27

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabrication of PIN and HEMTs

T-shaped Gate Overlay Reduce parasitic capacitance First level metallization 0.25 μm T-shaped gates are fabricated with e-beam lithography Air-Bridge : 1.8 μm Au N-Ohmic contact Passivation : Polyimide AR coating & Passivation : SiNx AuGe/Ni/Au Contact resistance of PD~0.1 Ω-mm

  • f HEMTs~0.3 Ω-mm

Low dark current SiNx completes AR Coating and passivate HEMTs P-Ohmic contact Ti/Pt/Au, sheet resistance ~ 205 Ω/□ Mesa & Undercut etching Isolation & low Junction capacitance

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SLIDE 28

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Ohmic Contacts for Photodiodes and HEMTs

Gaps between probe pads (μm)

2 4 6 8 10 20 40 60 80

Unalloyed n-ohmic of HEMTs Alloyed N-ohmic of photodiodes P-type ohmic of Photodiodes Unalloyed N-ohmic of Photodiodes Alloyed n-ohmic of HEMTs Linear Regression

Resistance (Ω)

Contact Resistivity (Ω-mm) Sheet Resistance (Ω/ ) Specific Contact Resistivity (Ω-cm2)

  • 1.9

210.5 1.73×10-4

■

0.3 205.2 1.13×10-6 ▼ 0.035 209.6 5.71×10-8 1.34 43.0 2.0×10-5

○

0.089 40.8 1.96×10-6

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SLIDE 29

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Fabricated Photodiodes and HEMTs

Source Drain

A photodiode with 10 μm-diameter

  • ptical window

A HEMT with 0.25 μm long gate

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SLIDE 30

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Characteristics of Photodiodes

Dark Current : 785 pA @ -5V Reverse Bias

Bias Voltage (V)

2 4 6 8 10 12 14 16

Dark Current (A)

10-11 10-10 10-9 10-8 10-7 10-6 785 pA @ 5V

Optical input power (dBm)

  • 15
  • 10
  • 5

5 10

Photocurrent (mA)

10-2 10-1 100 101

Dark Current vs. Bias Photocurrent vs. Pinc

Frequency (GHz)

0.5 5 50

Frequency Response (dB)

  • 12
  • 9
  • 6
  • 3

0 V

  • 1 V
  • 2 V
  • 3 V

Reverse bias voltage (V)

2 4 6 8 10 12 14 16

Bandwidth (GHz)

1 10 100

Measured Estimated

Frequency Responses@Various Bias

  • 3 dB Bandwidth v.s Bias voltages
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SLIDE 31

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

DC Characteristics of HEMTs

Gate Length = 0.25 μm, Gate Width = 100 μm

Drain-Source Voltage (V)

  • 1.5
  • 1.0
  • 0.5

0.0

Drain Current (mA/mm)

100 200 300 400 500 600

Transconductance (mS/mm)

100 200 300 400 500 600 700

Drain-Source Voltage (V)

0.0 0.5 1.0 1.5 2.0

Drain Current (mA/mm)

100 200 300 400 500 600

Idss = 530 mA/mm @ Vds=2V and Vgs=0 V Gm,max= 540 mS/mm @ Vds=2V and Vgs=-0.52 V

I-V Characteristics Transfer Characteristics

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SLIDE 32

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

RF Characteristics of HEMTs

fT = 134 GHz and fMAX = 191 GHz @ Vds=1.25 V and Vgs=-0.37 V

Frequency (GHz)

1 10 100

Current Gain (dB)

10 20 30 40 50

MSG/MAG (dB)

10 20 30 40 50

fT=134 GHz, fMAX=191 GHz VDS=1.25 V, VGS=-0.37 V

Drain Current (mA)

10 20 30 40 50

fT (GHz)

20 40 60 80 100 120 140 160

fT,max = 134 GHz @ Ids=27mA, Vgs=-0.37 V

Current, and Power Gain fT vs. Drain Current

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SLIDE 33

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Optoelectronic Receiver Design

  • 16 dB gain from DC to 40 GHz
  • Return loss (I/O) > 7 dB / 20dB

5 10 15 20 25 30 35 40 45 50 6 8 10 12 14 16 18 4 20 Frequency (GHz) Power Gain (dB)

  • 50 dBΩ (320 Ω) Transimpedance gain
  • Conversion gain ~ 169 V/W

Distributed Amp. only Photodiode Cascode Gain Cell

5 10 15 20 25 30 35 40 45 50 35 39 43 47 31 51 Frequency (GHz) Transimpedance (dB Ohm)

Photodiode + Distributed Amp.

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SLIDE 34

Micro and Nanotechnology Lab University of Illinois at Urbana-Champaign Advanced Processing and Circuits Group

Summary

  • Review of Metamorphic device Researches
  • Double heterojunction photodiodes and HEMTs were fabricated
  • n the metamorphic GaAs substrate

Photodetector 0.25 μm DHEMTs fT ~ 140 GHz fmax~ 190 GHz Bandwidth > 40 GHz Responsivity > 0.5 A/W Dark current < 1 nA

  • Opens up the possibility of monolithic OEIC on GaAs substrate

Simulated circuit performance Bandwidth ~ 40 GHz Transimpedance ~ 320 Ω, Conversion Gain ~ 169 V/W for long wavelength optical fiber communications