design of ingaas/inp 1.55 m vertical cavity surface ... · design of ingaas/inp 1.55μm vcsels i-...

Design of InGaAs/InP 1.55μm vertical cavity surface emitting lasers (VCSEL)

J.-M. Lamy, S. Boyer-Richard, C. Levallois, C. Paranthoën, H. Folliot, N. Chevalier, A. Le Corre, S. Loualiche

UMR FOTON 6082 CNRS, INSA de Rennes, France

[email protected]

8th International Conference on Numerical Simulation of Optoelectronic Devices, Nottingham, 4th September 2008

Design of InGaAs/InP1.55μm VCSELs

I- Introduction and context

II- Optical design of the VCSELsElectric field calculation

Bragg mirrors

III- Thermal analysis

IV- Buried Tunnel Junction

V- Conclusion

Soline Boyer-Richard, NUSOD’08, Nottingham, 4th September 2008

Fiber To The Home

Ideal optical source

• Low cost

• 1.55µm=>compatible with long haul transmission

• High frequency modulation

• Tunable =>WDMSoline Boyer-Richard, NUSOD’08, Nottingham, 4th September 2008

Surface Emitting Laser• Device tested before packaging• Array integration• Output circular mode shapeMicro-cavity• Small active region low Ith or Pth

• Short length Wide FSR

Advantages

VCSEL

Drawbacks Output powerThermal dependence

Substrate

Bottom mirror

Top mirror

active region 1~3 µm


Electrically pumped VCSEL


6QWs

InP n+

Q1.18 (30 nm)

Q1.18 (30 nm)

InP p+ Q1.18 p+ (10 nm) Q1.4 p++(25 nm) Q1.4 n++(25 nm) InP n+

Active zone

Bragg mirror

Bragg mirror

InP n+ Contact BTJ

CW 1.55 µm optically pumped VCSELs lattice-matched to InP with dielectric Bragg mirrors already demonstrated (J.M. Lamy et al., IPRM’08)

Electrically pumped VCSEL designed and fabricated at FOTON laboratory, within a collaborative ANR project named lambda-access

a-Si/a-SiNx DBR

active zone grown by MBE with 6 InGaAs QW on lattice-matched alloy In0.8Ga0.2As0.435P0.565 (Q1.18)

Buried Tunnel Junction in strongly doped lattice matched alloy Q1.4 (ND=NA=5.1019 cm-3)




Bragg mirrors



V- Conclusion



Optical simulation

0 1 2 3 4 5 6 7

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Ref

ract

ive

inde

x

Thickness (µm)

Ele

ctri

c fie

ld in

tens

ity

Bragg mirror

Bragg mirror

Active zone

BTJ

Electric field repartition in the structure

Optical simulation algorithm : 2 parts

Optical properties thickness, index,

absorption

Propagation matrices

Electric field

Reflectivity spectrum

Active zone characterization

QW energy levels

Oscillator strength → Gain

Absorption

Spontaneous emission

Monomode VCSEL structure around 1.55 µm


Bragg mirrors2 types of Distributed Bragg Reflectors realized by magnetron sputtering :

InP

Miroir de Bragg 6 paires

a_SiNx/a_Si

Bragg mirror6 periods

InP

Miroir de Bragg 3.5 paires

a_SiNx/a_Si

Bragg mirror3.5 periods

Au

Simulation based on propagation matrices

Same reflectivity (99.6 %) @ 1.55 µm in good agreement with FTIR results

Total reflectivity of the VCSEL cavity : Free Spectral Range > 50 nm → monomode VCSEL

Standard DBRHybrid DBR




Bragg mirrors



V- Conclusion



Thermal simulationVCSELs : Small active region → DBR → problem of heat dissipation

optical and electrical VCSEL thermal 2D finite element simulation

thermal resistance evaluation compared to experiment

Wavelenght shift as a function of pump power for optical VCSELs with standard or hybrid DBR.

10 20 30 40 50

1.566

1.568

1.570

1.572

1.574

1.576

1.578

1.580

1.582

0.22nm/mW

0.29nm/mW

Em

issi

on w

avel

engt

h (µ

m)

Pump power (mW)

conventional mirror hybrid mirror

Rth = 2.9 K/mW

Rth = 2.2 K/mW


Thermal simulation

Electrically pumped VCSEL 2D thermal

simulation.

0 1 2 3 4 5 6 7

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

Ther

mal

resi

stan

ce (K

/W)

InP thickness (µm)

Electrical VCSEL thermal resistance as a function of InP thickness (BTJ Ø 5 µm)

RTh = 2360 K/W for a 200 nm InP thickness VCSEL RTh = 2050 K/W (1 µm InP)

In

InPBragg mirror

Au

Active zone

Si3N4

Bragg mirror

InP

In

InPBragg mirror

Au

Active zone

Si3N4

Bragg mirror

InP

10 mW




Bragg mirrors



V- Conclusion



Objectives :

localized current injection : electrical carrier confinement

n-type contact, easier to realize and less resistive

small threshold voltage and small serial resistance to limit self-heating

Theoretical operation : I(V) characteristics

V

I

Inverse : tunnel current

Direct : Vd > Vthres

Classical diode

negative resistance :

Jtunnel when Vd

25 nm

Vd = 0

EvN

EcN

EcP

EvP

tunnel diode : EcN < EF< EvP

EF

Buried tunnel junction


Objectives :





V

I



Classical diode


Jtunnel when Vd

Vd = -0.5 V


Jtunnel


Objectives :





V

I



Classical diode


Jtunnel when Vd

Vd = 0.2 V


No tunnel currentVd<Vthres_diode


Objectives :





V

I



Classical diode


Jtunnel when Vd

Vd = 0.5 V


Vd >Vthres_diodeDirect classical

diode



Jonction tunnel

Substrat InP n

Co ac c cu a e : / u

InP n++

InP p++

InGaAs p+ InP p+

InP n+

Q1.18 p++ Q1.4 p++ Q1.4 n++

0.2 µm 0.15 µm

0.1 µm 10 nm 25nm 25nm 0.1 µm 0.3 µm

Tunnel junction

P-type contact

n-type contact

Experimental study ofthe BTJ :

I(V) characteristics

-600

-400

-200

0

200

400

600

-0,2 0 0,2 0,4 0,6 0,8 1J

(A/c

m2 )

Vd (V)

N = 5.1019 cm-2

Vthres

= -36 mV

Rinverse

= 2.4.10-4 Ω.cm2


Buried tunnel junction1D Schrödinger-Poisson simulation useful to :

verify the tunnel effect in the reverse BTJ

avoid current leakage in the reverse InP junction outside the BTJ

-6

-5

-4

-3

-2

-1

0

Ene

rgy

(eV

)

Active ZoneQ1.18 153 nm

InP p+30 nm

BTJ

InP n

InP n

InP n

VB

VB

CB

CB

outside the BTJ

Simulation of the band diagram of the VCSEL in vertical direction, inside and outside the BTJ

-2 -1 0 1 2 3 4-2

-1

0

1

2

I (m

A)

V (V)

3944 BTJ:7µm 3944 without BTJ 4008 without BTJ 4008 BTJ:7µm

I(V) characteristics of the VCSEL cavities (without DBR)

3944 : 15 nm InP p+ leakage current

4008 : InP p+ = 240 nm …OK


Conclusion3 steps of simulation to design electrically pumped VCSELs :

Optical simulation → epilayer structure and DBR reflectivity

Thermal analysis → thermal resistance and contact design

Schrödinger Poisson 1D → avoid leakage current around the BTJ

… towards an integrated model ?

100µm

First electrical VCSEL sample from FOTON laboratory

measurement in progress…

design of ingaas/inp 1.55 m vertical cavity surface ... · design of ingaas/inp 1.55μm vcsels i-...

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