Present status and future prospects of Bi-containing semiconductors

M. Yoshimoto and K. OeDept. Electronics,

Kyoto Institute TechnologyJapan

Acknowledgement

RBS: Prof. K. Takahiro (Kyoto Inst. Tech.), Dr. A. Chayahara (AIST)

Photoreflectance: Prof. T. Kita (Kobe Univ.)

EXAFS: Prof. M. Tabuchi, Prof. Y. Takeda (Nagoya Univ.)

Raman spectroscopy: Prof. Harima , Dr. P. Verma (Kyoto Inst. Tech.)

Post. Doc. Dr. W. Huang, Dr. G. Feng

Graduate students: Mr. S. Murata, Mr. Y. Tanaka,

Ms. Y. Tominaga, Mr. K. Yamada, Mr. T. Fuyuki

0utlineBackground

MOVPE growth of GaAsBi and InAsBiRBS、Raman、EXAFS: substitutional incorporation of BiPhotoluminescence, Photoreflectance: temperature-insensitive EPL, Eg

MBE Growth of GaAsBiGaAsBi growth: surfactant-like effect of Bi atomGaNAsBi and InGaAsBi: expansion of luminescence wavelengthGaAs/GaAsBi multi-quantum wells: smooth interface w/o segregation

Device-quality epilayersLaser emission from GaAsBi by photo-pumpingIssue of GaAsBi growth

Summary

Earliest days of epitaxy of Bi-containing semiconductors

MBE growth of InSbBi to obtain III-V alloys with the narrowest possible band gap.

① K. Oe, S. Ando, K.Sugiyama: Jpn. J. Appl. Phys. 20 (1981) L303.② A.J.Noreika, W.J. Takei, H. Francombe and C.E.C Wood: J.Appl.Phys. 53

(1982) 4932

Key to growth

low-temperature growth

K. Oe, et.al:JJAP Sb/In≒1 Sb/In<1

InSbBi↓

☺mirror-likesurface

rough surface(Sb inclusion)

InSb sub.↓

Sb/In>1

no growth of InSbBi

↓

★Wavelength-Division Multiplexing (WDM) GaInAsP laser diode (LD): temperature dependence of bandgap and refractive index⇒ fluctuation of lasing wavelength

LD equipped with Peltier device⇒ drawback: cost, energy consumption

★Materials with low ΔEｇ/ΔT⇒ LD with an emission of temperature-insensitive

wavelength: elimination of Peltier device

Why low ΔEｇ/ΔT ?

Dense WDM (example)λ Division: 0.4 nm/channel

Laser diode Δλ/ΔT: 0.1 nm/K

Proposal of GaInAsBi as a active-layer materials of LDK. Oe and H. Asai, Proc. Electronic Materials Symp. ’95, Izu, Japan p.191

Semiconductor : GaAs Semimetal: GaBi ⇒ Alloy : GaAsBi

X-ray diffraction pattern

Successful epitaxial growthLattice constant increases with GaBi molar fraction.

GaBi molar fraction: Rutherford backscattering spectroscopyThermally stable after anneal in As pressure at 560oC for 30min

MOVPE growth of GaAsBiLow-pressure MOVPE Sources: TIPGa, TMBi, TBAs, Substrate: GaAs(100)Growth temperature: 365oC Growth rate: 1μm/h

K.Oe, JJAP 41 (2002) 2801

0 0.2 0.4 0.60.0

2.0

4.0

Determination of GaBi molar fraction x for GaAs1-xBix

⇒determination of GaBi molar fraction by X-ray diffraction

Angular Spacing in X-ray diffraction Δ2θ(deg)

GaB

i Mol

ar F

ract

ion(

%)

Fitting Functionx=6.93 Δ2θ

Rutherford backscattering spectroscopy(RBS)

K. Takahiro, et.al, J. Electron. Matter. 32 (2003)34. M.Yoshimoto, et.al, JJAP 42 (2003) L1235

Angular scan in Rutherford backscattering spectroscopy

Angular yield profile for [100] and [110] channel

Yield(Bi)=Yield(Ga+As)

⇒Bi atoms are located exactly on substitutional sites.

Note

Interstitial site in a zinc-blend lattice

[100]: shadowed, [110]: visible

K. Takahiro, et.al, J. Electron. Matter. 32 (2003)34.

GaBi-like and InBi-like modes⇒substitutional incorporation of Bi atoms

Raman spectroscopy and EXAFS of GaAsBi and InAsBi

H.Ofuchi, et.al JJAP 38 (1999)Suppl. 38-1, 545 P. Verma, et.al JAP 89(2001) 1657

The majority of Bi atoms substituted the As site of InAsBi

Temperature dependence of PL for GaAsBi

K.Oe, JJAP 41 (2002) 2801

Photoreflectance spectra of GaAsBi

GaAs0.995Bi0.005

Franz-Keldysh oscillation due to built-in electric field

Decrease in bandgap of GaAs1-xBixwith increasing GaBi molar fraction

GaBi molar fraction (%)

J.Yoshida, et al., JJAP 42 (2003) 371

Temperature dependence of bandgap of GaAsBi

GaBi molar fraction

ΔEg/ΔT150-300K(meV)

0 (GaAs) -0.420.005 -0.240.013 -0.230.026 -0.15

1.2

1.3

1.4

1.5

0 50 100 150 200 250 300

Ban

dgap

Ene

rgy

(eV

)

Temperature (K)

x = 0

x = 0.005

x = 0.013

x = 0.026

J.Yoshida, et al., JJAP 42 (2003) 371

Temperature-insensitive bandgap

Drawbacks of MOVPE growth of GaAsBi×MOVPE: • insufficient decomposition of metalorganic at low Tsub

⇒difficulty in incorporation of In with existence of Ga at low Tsub• segregation of Bi on surface

○MBE: • low-temperature growth without decomposition process• no Bi segregation: desorption from surface

X-ray diffraction Bi-flux dependence

Thickness: 0.5 μmSubstrate temperature: 380 oC Ga flux: 3×10-7 TorrAs flux: 8×10-6 Torr

65.5 66 66.50

2

4GaAsBi(004)K 1α

K 1α

K 2α

K 2αGaAs(004)

K 1α

K 1α

K 1α

Bi flux (x10–8Torr)

0

2

4

6

8

INTE

NS

ITY

(ar

b. u

nits

)

2 (deg)θ

Lattice constant increases with Bi flux, followed by saturation.

MBE Growth of GaAsBi

M.Yoshimoto, et.al, JJAP 42 (2003) L1235RBS: Substitutional incorporation of Bi

GaBi molar fraction vs. Bi flux and substrate temperature

0 5 10

0.0

2.0

4.0

360 380 400 420

Bi FLUX (x10–8Torr) SUBSTRATE TEMPERATURE (oC)

GaB

i MO

LAR

FR

AC

TIO

N x

(%)

(a) (b)

Bi flux 2.8x10–8Torr

Tsub=380oC

M.Yoshimoto, et.al, JJAP 42 (2003) L1235

Effect of As flux on MBE growth of GaAsBi

Thickness: 0.5 μmSubstrate temperature: 380 oC Ga flux: 3×10-7 TorrBi flux: 2×10-8 Torr

Bi is incorporated with a limited As flux.

☺As/Ga≒1

As/Ga>1

As/Ga<1

M. Yoshimoto, et.al, Mater. Res. Soc. Symp. Proc. 891 (2006) 0891-EE11-06

0.9 1.0 1.1 1.2 1.3

380oC

360oC

350oC

In

tens

ity (a

rb. u

nit)

Photon energy (eV)0 1 2 3 4 5 6

1.0

1.1

1.2

1.3

1.4

PL

peak

em

issi

on (e

V)

GaBi molar fraction

R.T. PL spectra of GaAsBi grown at different T

PL peak energy vs. GaBi molar fraction

(%)

Photoluminescence from GaAsBi

Luminescent GaAsBi can be obtained by low-temperature MBE growth (<400oC), probably due to a surfactant-like effect of Bi atoms.

W.Huang, et.al, JAP 98(2005) 053505

Plasma-assisted MBE

GaAs buffer layer (thickness: 100nm, Tsub 500oC)

GaNAsBi substrate temperature: 350~400oCsource: Ga (10-7Torr), As (10-6Torr), Bi (10-8Torr)

plasma activated nitrogen(13.56MHz)

Key to Bi incorporation:●narrow process window for As flux ●low-temperature growth (<400℃）

[110]

[110]GaNAsBi RHEED -

Expansion of luminescence wavelength to longer wavelength － GaNAsBi

M. Yoshimoto, et.al, JJAP, 43 (2004) L845

GaNAsBi: composition determination

GaBi molar fraction by RBS

0 200 400 600100

102

104

106

Bi

Ga+N

Ga

As

DEPTH (nm)

SIM

S Y

IELD

(arb

. uni

ts) GanAsBi GaAs sub.

GaN molar fraction by SIMS

Substitutional incorporation of Bi atoms were also confirmed by channeling RBS.

M. Yoshimoto, et.al, MRS Symp. Proc. 891 (2006) 0891-EE11-06

X-ray diffraction of GaNAsBi

Constant supplies of Ga, As, Bi

Lattice matched to GaAs

W.Huang, et.al, JAP 98(2005) 053505

PL emission from lattice-matched GaNAsBi

Ga(N0.34Bi0.66)zAs1-z : Lattice matched to GaAsPL emission in the optical fiber communication waveband

Ga(N0.34Bi0.66)zAs1-z

M. Yoshimoto, et.al, 16th IPRM, Kagoshima, Japan, 2004, IEEE #04CH37589, p.501.W.Huang, et.al, JAP 98(2005) 053505

Photoluminescence of GaNAsBi

Low temp. coefficientLow temp. coefficient

Temperature coefficient of the PL peak energy ★ 0.14 meV/K (150-300k) = 1/3 InGaAsP ★

W.Huang, et.al, JAP 98(2005) 053505

0 60 120 180

Inte

nsity

(arb

. uni

ts)

T ime (sec.)

GaAsBi GaAsBiGaAs

[110]

[110]

[110] [110]

[110] [110]

Growth of GaAsBi Multi-quantum wells

Layer-by-layer growth

Y. Tominaga, et.al, APL 93 (2008)131915

(400) X-ray diffraction pattern

61.0 62.0 63.0 64.0 65.0 66.0 67.0 68.0

Simulation fitting Experimental data

MQW

-7th-6th

-5th-4th

-3rd

-2nd

+3rd+2nd

-1st +1st0th

GaAs

Inte

nsity

(arb

. uni

ts)

2θ (degree)

65.2 65.4 65.6 65.8 66.

GaAs0.948Bi0.052 layer / GaAs layer = 7nm / 14nm, 14periods

0th-1st

1211

1098765432

1

Inte

nsity

(arb

. uni

ts)

2θ (degree)

Smooth interface

• Laue function: N’=N-2

Cross-sectional TEM image

GaAs0.952Bi0.048/GaAs MQWs (Growth temperature:350°C)

Y. Tominaga, et.al, APL 93 (2008)131915

Quantum size effect

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

GaAs0.948Bi0.052 / GaAs = 3~12nm / 14nm, 10~15 periods

Photon energy (eV)

1.0

0.8

0.6

0.4

0.2

0.0Nor

mal

ized

inte

nsity

(arb

. uni

ts)

RT3nm5nm7nm

12nm

◆Photoluminescence (PL) spectra of GaAs1-xBix/GaAs MQW

1.16

1.14

1.12

1.10

1.08

1.06

RT

PL p

eak

ener

gy (e

V)

Thickness of GaAsBi layer (nm)2 4 6 8 10 12

GaAs0.949Bi0.051 thin film

Excitation wavelength : 488nm (Ar+ laser)

Y. Tominaga et al.:PSS(c) 5, 2719 (2008)

PL at a wavelength of 1.3µm

0.0 2.0 4.0 6.0 8.0 10.0 12.0

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.0 1.1 1.2 1.3 1.4 1.50.0

0.2

0.4

0.6

0.8

1.0

1.2

GaAs1-xBix / GaAs = 7nm / 14nm, 5~10 periods

Wavelength (µm)

Nor

mal

ized

PL

inte

nsity

(arb

. uni

ts)

Bi content (%)

PL p

eak

wav

elen

gth

(µm

)3.1% 4.8% 6.8%8.1%

9.3%10.9%

RT

◆PL spectra of GaAs1-xBix / GaAs MQWs

Y. Tominaga, et.al, APL 93 (2008)131915

Thermal stability

64.5 65.0 65.5 66.0 66.5 67.0

500oC

600oC

700oC

800oC

900oC

temperatureAnnealing

-3rd -2nd-1st 1st

MQW 0th GaAs

XR

D in

tens

ity (a

rb. u

nits

)

2θ (degree)

GaAs0.984Bi0.016/GaAs MQW◆Annealing:10 minutes under N2 flow

Y. Tominaga, et.al, APL 93 (2008)131915

Laser emission from GaAs1-xBix by photo-pumping

900 950 1000 1050 11000

1x104

2x104

3x104

4x104

5x104

6x104

2.4mJ/cm22.5mJ/cm2

3.3mJ/cm2

GaAs

GaAsBi

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)

RT

1.0 1.5 2.0 2.5 3.0 3.5

RT

Inte

grat

ed in

tens

ity (a

rb. u

nits

)

Pumping density (mJ/cm2)

GaAs0.975Bi0.025

Y. Tominaga, et.al, Appl. Phys. Express 3 (2010) 062201

Laser emission from GaAs1-xBix by photo-pumping

900 950 1000 1050 11000

1x104

2x104

3x104

4x104

5x104

6x104

2.4mJ/cm22.5mJ/cm2

3.3mJ/cm2

GaAs

GaAsBi

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)

RT

1.0 1.5 2.0 2.5 3.0 3.5

RT

Inte

grat

ed in

tens

ity (a

rb. u

nits

)

Pumping density (mJ/cm2)

GaAs0.975Bi0.025

Y. Tominaga, et.al, Appl. Phys. Express 3 (2010) 062201

900 950 1000 1050 11000

1x104

2x104

3x104

4x104

5x104

6x104

0.72mJ/cm20.83mJ/cm2

0.91mJ/cm2

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)

240K

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Inte

grat

ed in

tens

ity (a

rb. u

nits

)

Pumping density (mJ/cm2)

240K

31

Temperature dependence of lasing wavelength

GaAs0.975Bi0.025

Low-temperature coefficient of lasing wavelength

GaBi molar fraction

ΔEPL/ΔT150-300K(meV/K)

0 (GaAs) -0.420.025(Laser) -0.180.025(PL) -0.15

100 150 200 250 3001.20

1.25

1.30

1.35

Temperature (K)

Emis

sion

ene

rgy

(eV

)

10-1

100

101

Threshold pumping density (m

J/cm2)

T0=83K

Y. Tominaga, et.al, Appl. Phys. Express 3 (2010) 062201

Key to InSbBi growth (1981)

low-temperature growth

InSbBi↓

↓

↓

Sb/In≒1 Sb/In<1

☺mirror-likesurface

rough surface(Sb inclusion)

InSb sub.Sb/In>1

no growth of InSbBi

↓

low-temperature growth ☺As/Ga≒1

Key to GaAsBi growth (at present)

As/Ga>1

As/Ga<1

narrow window of As/Ga ratio

narrow window of Sb/In ratio

Issue of GaAsBi growth

Issue of GaAsBi growth

The essence of growth conditions for GaAsBi-based alloys is exactly the same as that of InSbBi growth in the early 80s!!

Conventional essencelow temperature growth (<400oC) As (or Sb) flux adjustment in a limited range on the brink of As (or Sb) shortage on the growing surface

An innovative growth technique is expected for further improvement in GaAsBi-based alloys.

growth condition A (temperature etc.)

grow

th c

ondi

tion

B(fl

ux e

tc.)

process windowfor GaAsBi growth single crystalline

luminescentlaser emission

very narrow process window for laser emission

SummaryMOVPE growth of GaAsBi and InAsBi

Bi atoms occupy substitutional sites (RBS, Raman, EXAFS).A single-peak PL (10 – 300K).Temperature dependence of Eg of GaAs0.974Bi0.026 is 1/3 of the value of GaAs.

MBE growth of GaAsBiKey to growth: (1)Control of As flux within narrow limits, (2)low-temperature growth. A surfactant-like effect: Luminescent GaAsBi grown at low temperature (<400oC).Expansion of luminescence wavelength to longer wavelength

GaNAsBi/GaAs: fairly luminescent (1.4 μm emission）.InGaAsBi/InP: weak luminescence (extremely low temperature growth <300 oC).

MQW structure: abrupt interface w/o segregation, thermally stable (<800 oC),luminescent (1.3 μm@10.9%Bi), quantum-size effect.

Device-quality epilayerLaser-emission can be obtained, however, very narrow process window. The essence of growth conditions for GaAsBi-based alloys is exactly the same as that of InSbBi growth in the early 80s!!An innovative growth technique is expected for further improvement in GaAsBi-based alloys.