iii-v and group iv epitaxy for low energy optoelectronics · 2018-10-31 · iii-v and group iv...

A Science & Technology Center

III-V and Group IV Epitaxy for Low Energy Optoelectronics

Christopher Heidelberger1, Seth Fortuna2, Ming Wu2, Eugene A. Fitzgerald1

1Department of Materials Science and Engineering, Massachusetts Institute of Technology

2Department of Electrical Engineering and Computer Sciences, University of California, Berkeley

September, 2017


Outline

Materials for optical linkHBT integration for high performance

communicationLikely application for these technologies

E3S Seminar 4/13/2017


Active region p-doping analysis from UC Berkeley


Assumptions:(1) Surface recombination

velocity = 3e4 cm/s(2) Auger recombination

coefficient = 2e-29 cm-6s-1(3) Sp. Em. Enhancement = 640,

Antenna Efficiency = 45%Q-factor = 37

(4) Bulk SRH ignored(5) Injection carrier density =

1.5e18cm-3

Target


Growth of undoped LED structure


InP (substrate)

InP bottom contact 300 nm

InGaAsP barrier

InGaAs QWInGaAsP barrier

InGaAs QWInGaAsP barrier

InGaAs QW

InGaAsP barrier

60 nm

6 nm10 nm6 nm10 nm6 nm

40 nm

InP top contact 30 nm

InGaAs top contact 40 nm

LED structure schematic: XTEM

HT = 200 kV, (110) on pole


Luminescence of undoped LED structure


>10X increase in quantum efficiency

MQW (MIT)

Previousdesign (outsidevendor)

1450 1500 1550 1600 1650

(nm)

0

0.2

0.4

0.6

0.8

1

Inte

nsity

(arb

.)

PL of blanket film

1550 nm target

Quantum efficiency (large-area LEDs, UC Berkeley)


LED structure with Zn p-type doping


undoped active region:

p+ active region (Zn doping ~ 5 x 1018):

InGaAs contact

InP contact

InGaAs/InGaAsPMQW

InP contact

InGaAs/InGaAsPMQW

DIC Image

PL of Blanket Films

1450 1500 1550 1600 1650

(nm)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Inte

nsity

(arb

.)

undoped

5 x 10 18 cm -3 Zn doping x100

poor EL and IV characteristics for fabricated LED


Lattice matched growth

7

InP substrate (S-I)

InP regrowth, UID20 nm

InGaAs, C-doped200 nm

InP cladding, UID10 nm

600 C

500 C

550 C

Growth temperature

V/III ratio = 4CBrCl3 ratio = 9%

p = 3.2 x 1018 cm3

qx (nm-1)

qz (n

m-1

)

4.815 4.82 4.825 4.83 4.8356.74

6.76

6.78

6.8

6.82

6.84

6.86

6.88

InP substrate

InGaAs

fully strained

In fraction = 52.2%


Post-growth N2 anneal: effect on PL intensity and lifetime

Decrease in intensity/lifetime after post-growth anneal increased Auger recombination due to higher hole concentration

Laser power = 500uWWavelength = 1000nm20X objective

without anneal

with anneal 𝜏𝜏 ≈ 140ps

𝜏𝜏 ≈ 700ps

Time-resolved (UC Berkeley)

without anneal, 3.2 x 1018 cm-2

with anneal, 1 x 1019 cm-3

1400 1500 1600 1700 1800 1900

(nm)

10 -2

10 -1

10 0

Inte

nsity

(arb

. uni

ts)

UID In0.53

GaAs control

In0.52

GaAs; 3.2x10 18 cm -3 ; no anneal

In0.52

GaAs; 1.0x10 19 cm -3; 500 C, N2, 10 min anneal


InGaAs LED structures: conclusions

Demonstrated undoped InGaAs/InGaAsP LED structure with good morphology and high quantum efficiency

Grew C-doped InGaAs with p > 1 x 1019 cm-3 and recombination limited by Auger recombination

Future work Grow InGaAsP cladding layers at similar growth conditions as C-doped

InGaAs Grow and characterize InGaAs/InGaAsP LED structure with high p-type

doping Fabricate and test antenna-enhanced LED structure with heavily-

doped active region (UC Berkeley)



GaAsP/InGaP HBT on Si

heterojunction bipolar transistor (HBT): high frequency (& independent of litho) high power efficiency

GaAsP/InGaP


EBIC measurements of GaAsP HBTs

GaAsP subcollector (n+)

GaAsP collector (n)

GaAsP base (p+)

InGaP emitter (n+)

GaAsP contact (n++)

Current Amplifier

Signal Conditioning

Computer/

Display

electron beam

ohmic contact

e-h pairs generated

𝑉𝑉𝐴𝐴ΔSiGe graded buffer (n+)

Si substrate (n+)


Experimental loop

12

Epitaxial Growth

(MOCVD)

Fabricate HBTsEBIC + Electrical

Measurements

Design Structure

0.4 0.6 0.8 1 1.2 1.4

VBE (V)

10 -12

10 -10

10 -8

10 -6

10 -4

10 -2

I C, I

B (

A)

IC

IB


Iterative approach to improved defect density

C base doping

Zn base doping

improved InGaP

calibration

thick subcollector

layer

Misfit Dislocation

Density

Modification

1900 cm-1

EBIC

900 cm-1 600 cm-1 < 1 cm-1

30 µm


High current gain demonstrated on Si substrate

GaAsP subcollector (n+)

GaAsP collector (n)

GaAsP base (p+)

InGaP emitter (n+)

GaAsP contact (n++)

ΔSiGe graded buffer (n+)

Si substrate (n+)

C base doping

Zn base doping

improved InGaP

calibration

thick subcollector layer

Modification

0.5 1 1.5 2 2.5

VBE (V)

10 -12

10 -10

10 -8

10 -6

10 -4

10 -2

I B,

IC

(A

)

IC

IB

60 µm diameter HBT

𝛽𝛽 = 156

= 3.7 × 106 cm-2

< 1 cm-1

30 µm

C. Heidelberger and E. Fitzgerald, J. Appl. Phys., under review


• combined models for threading and misfit dislocations

• misfit dislocations have pronounced effect on current gain, even at low densities

C. Heidelberger and E. Fitzgerald, J. Appl. Phys., under review

“Current Gain Map”


Applications/Market: Is Computing a Target Market? 28nm likely to be ‘last profitable node’ for non-monopolistic market

participants? De-integration occurring for performance and market reasons Computing cores will be mature for a decade or more Data center ‘farms’ or even ‘cities’

• Key necessary innovations obscured by monopolistic corporate structure• University research likely irrelevant to key problems without an informing paradigm

Communication and power management take front-seat• Within-data-center more important for silicon ICs because of market size• i.e. telecom thinking must leave silicon photonics (i.e. = telecom photonics)

What to do in next decade or two? Disruptive* path suggests key silicon technology (with new added value in

materials) to appear in communication, lighting, and power management ICs; new era of ASICs• Nothing to do with data centers, computing, etc. initially• Grow in other markets for decades, then spill back into computing

– Real 5G wireless– Visible integrated optoelectronics

• Old silicon nodes (and 200mm) are playground and commercialization for innovation

*Actual Christensen definition, not Valley term

iii-v and group iv epitaxy for low energy optoelectronics · 2018-10-31 · iii-v and group iv...

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