MIRTHE Summer Workshop 2014, 04-08 August

Four-zone quantum well infrared photodetector with

a confined state in the continuum

G. M. Penello, A. P. Ravikumar, D. L. Sivco and C. Gmachl

2MIRTHE Summer Workshop 2014, 04-08 August

Motivation– Explore electron confinement by

using electronic Bragg mirrors– Extend the energy range of III-V

QWIPs (InGaAs/InAlAs lattice matched to InP)

– Mid-IR application– Gas sensing systems – Free space communication

http://en.wikipedia.org/wiki/Dielectric_mirror

P. Kluczynski et al., Appl. Phys. B: Lasers and Opt., 105, 2, 427–434 (2011).

http://en.wikipedia.org/wiki/L_band

3MIRTHE Summer Workshop 2014, 04-08 August

QWIP

Continuum

-10 -5 0 5 100

200

400

600

800

Ene

rgy

(meV

)

Position (nm)

Bound to continuum

Quantum Well Infrared Photodetector

-10 -5 0 5 100

200

400

600

800

Ene

rgy

(meV

)

Position (nm)

Bound to bound

-10 -5 0 5 100

200

400

600

800

Ene

rgy

(meV

)

Position (nm)

Bound to quasibound

Continuum Continuum

• High selectivity (narrow absorption peak)

• Tunable for a fixed bandoffset

• Poor carrier extraction

• Easy carrier extraction• Tunable for a fixed

bandoffset• Lower selectivity (broad

absorption peak)

• Good selectivity (narrow absorption peak)

• Easy carrier extraction• Limited tunability for a

fixed bandoffset

4MIRTHE Summer Workshop 2014, 04-08 August

Bragg mirror

Refraction and reflection

-20 -10 0 10 20

0

200

400

600

800

Ener

gy (m

eV)

Position (nm)-30 -20 -10 0 10 20 30

0

200

400

600

800

Ener

gy (m

eV)

Position (nm)Bragg mirror for electrons

Electron with energy higher than the barrier

Electron with energy lower than the barrier reflection on the interface

refraction on the interface

reflection on a layered material

Electron with energy satisfying the bragg condition

How to confine an electron in the continuum?

5MIRTHE Summer Workshop 2014, 04-08 August

Continuum-localized states• “Defect” on the superlattice.

“defect”

• Increase transition energy• High selectivity• Easy carrier extraction

• Tunability not limited by bandoffset • Low thermal excitation

E

z Bragg mirrorBragg mirror

Miniband is not shown for clarity

6MIRTHE Summer Workshop 2014, 04-08 August

200 300 400 500 600-0.20.00.20.40.60.81.0 Photocurrent

Simulation - Best fit

Norm

alize

d ab

sorp

tion

and

phot

ocur

rent

Energy (meV)

-6.00E-008-4.00E-008-2.00E-0080.00E+0002.00E-0084.00E-0086.00E-008

Continuum-localized states

E0

E1

E2

E0→E1E0→E2

Photocurrent

• Increase transition energy• High selectivity• Easy carrier extraction

• Tunability not limited by bandoffset • Low thermal excitation

Central QW = 2.5 nmLateral QWs = 2.0 nmBarriers = 7.0 nm

Best fit CQW: 2.4 nm LQWs: 1.7 nm Barriers: 6 nm

Work done in collaboration with M. H. Degani, M. Z. Maialle, R. M. S. Kawabata, D. N. Micha, M. P. Pires, and P. L. Souza.

7MIRTHE Summer Workshop 2014, 04-08 August

Asymmetric QWIP with a confined state in the continuum

• Asymmetric structure to explore a photovoltaic QWIP and a bias dependence of the photocurrent.

High selectivity Easier carrier extraction in one direction Low thermal excitation

E

z

8MIRTHE Summer Workshop 2014, 04-08 August

Four-zone QWIP with a confined state in the continuum

1 – emission zone2 – drift zone3 – capture zone4 – tunneling (repopulation) zone

1

2

3

4

1

2

3

4

1

2

3

4

9MIRTHE Summer Workshop 2014, 04-08 August

SimulationAsymmetric sample

Bound to continuum QWIP Bound to bound QWIP(confined state in the continuum)

Reference sample

9 7 7 7 7 7 79

• Monolayer = 0.29343 nm– LQW = 7 monolayers ~– DQW = 9 monolayers ~– Barriers = 24 monolayers ~

• Absorption cross section– Transfer matrix method– FWHM = 30 meV ~ 0.1 (Typical in bound to bound transition)

2.1 nm2.6 nm 7.0 nm

2000 2500 3000 3500

0.0

0.5

1.0

Abs

orpt

ion

(u.a

.) Reference Asymmetric

Wavenumber (cm-1)

250 300 350 400Energy (meV)

• InGaAs / InAlAs lattice matched to InP

10MIRTHE Summer Workshop 2014, 04-08 August

Samples• MBE

– InGaAs / InAlAs lattice matched to InP– n-doped (2x1018 cm-3)– Active layers repeated 20x separated by 30 nm InAlAs– InGaAs contact layers n-doped (2x1018 cm-3)

• Processing– Wet etch – Ti/Au metallization– 45o lapping– Au wire bond

QWIP mesa

n-doped

Reference sample

Asymmetric sample

11MIRTHE Summer Workshop 2014, 04-08 August

Photocurrent

• Excellent agreement between theoretical and experimental results. • Photocurrent observed without applied bias on the asymmetric sample

– “Four zone” photovoltaic QWIP

80K 0V

1000 1500 2000 2500 3000 3500 4000

0.0

0.5

1.0

0.0

0.5

1.0

Wavenumber (cm-1)

Experimental data Simulation

Abs

orpt

ion (u

.a.)

Phot

ocur

rent

(u.a

.)

150 200 250 300 350 400 450Energy (meV)

80K-5V

1000 1500 2000 2500 3000 3500 4000

0.0

0.5

1.0

0.0

0.5

1.0

Energy (meV) Experimental data Simulation

Wavenumber (cm-1)

Abs

orpt

ion (u

.a.)

Phot

ocur

rent

(u.a

.)

150 200 250 300 350 400 450

Asymmetric sampleReference sample

12MIRTHE Summer Workshop 2014, 04-08 August

Photocurrent

2000 2500 3000

0.0

0.5

1.0Reference

+5.0V Asymmetric

+5V

@80K

Phot

ocur

rent

(a.u

.)

Wavenumber (cm-1)

5.5 5 4.5 4 3.5Wavelength (m)

2000 2500 3000

0.0

0.5

1.0Reference

-5.0VAsymmetric

-5V

@80K

Phot

ocur

rent

(a.u

.)

Wavenumber (cm-1)

5.5 5 4.5 4 3.5Wavelength (m)

“Leaky” localized stateMore extended states to couple

Broad photocurrent peakSimilar to the reference sample

Localized stateLess extended states to couple

Narrow photocurrent peak

13MIRTHE Summer Workshop 2014, 04-08 August

Conclusion and future steps• Asymmetric heterostructure with a confined state in the

continuum was designed• Photocurrent measurements confirmed the confined state in

the continuum• Photocurrent signal at 0V - photovoltaic QWIP • Bias dependent photocurrent was explained by the

asymmetry of the sample

• Figures of merit to be measured (responsivity and detectivity)• “Four zone” photovoltaic QWIP to be optimized in our

structure• New heterostructures using the confined states in the

continuum to be explored

14MIRTHE Summer Workshop 2014, 04-08 August

Acknowledges• Qcllab • Capes Foundation, Ministry of Education of Brazil.• MIRTHE (NSF-ERC)