x-ray diffraction analysis of Ⅲ-Ⅴ superlattices : characterization, simulation and fitting

$: X-Ray Diffraction Analysis of Ⅲ-Ⅴ Superlattices : Characterization, Simulation and Fitting$
X-Ray Diffraction Analysis of -Ⅲ Ⅴ Superlattices:Characterization, Simulation and Fitting

1

Xiangyu WuEnlong Liu

Mentor: Clement MercklingEPI Group @ imec

Project Work Nanoscience

Outline

2

Introduction XRD

• Principle• Superlattice Diffraction

Results and Discussions• Sample Structure• XRD Experiments Results• Curves Analysis and Simulation

Peaks Belonging Theoretical Calculation Simulation Results

Comparison with TEM Results Conclusion

Outline

3

Introduction XRD





Introduction

4

Superlattice (SL) is a periodic structure of layers of two (or more) materials. It can also refer to a lower-dimensional structure such as an array of quantum dots or quantum wires.

J.J.Gu, et al. IEDM12-529

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

http://mbe.rcast.u-tokyo.ac.jp/index_eng.htmlM. Cooke. - s Review, 2006 19(6): Ⅲ Ⅴ22-26

S.Y. Cheng, et al. Solid-State Electronics, 1999, 43(4):755-760.

Superlattice is linked to very advanced and complicated heterostructures.

Introduction

5

• Issue of TEM: • Only used to characterize small

area on wafer;• Need sample preparation, very

time-consuming;• Limit information, only thickness

X-Ray Diffraction

• SL Growth

EpitaxySlow growth rate

Interfacial layer control

Vapor Phase Epitaxy (VPE)Molecular Beam Epitaxy (MBE)

• Characterization: Transmission Electron Microscopy (TEM)

J.Warga, et al. Physica E, 2009, 41(6): 1040-3.

Dark: Er-doped silicon-rich nitride;Bright: Si.

Outline

6

Introduction XRD





XRD: Principle

n 2 sind

Bragg`s Law:Two beams with identical wavelength and phase approach a crystalline solid and are scattered off two different atoms within it. The lower beam traverses an extra length of 2dsinθ. Constructive interference occurs when this length is equal to an integer multiple of the wavelength of the radiation.

Bragg`s Law

XRD: Principle

8

sw 2q

X-ray tube

Detector

• ω: Tune the angle between the emitter and substrate;

• 2θ: Tune the angle between emitter and detector;• Ψ: Vertical rotation of substrate plane;• Φ: Horizontal rotation of the substrate plane;• x, y, z coordinate: move the substrate plane up,

down, left, right, without rotation

XRD: Principle

9

Incident beam

Omega axis

sample

Mono-chromator

detector

Omega axisdet

ecto

rAnalyzer

sample

Mono-chromator

detector

2θω

ω

Omega36.55136.12635.70135.27634.85134.42634.00133.57633.15132.726

Omega-2Theta36.55136.12635.70135.27634.85134.42634.00133.57633.15132.726

Si

Si

Si(Ge)

2θ=2ω+offset

Rocking curve vs Coupled scan

Outline

10

Introduction XRD





XRD: Superlattice Diffraction

11

The greatest use of HRXRD in industry is the characterization of epitaxial structures on compound semiconductors.

The composition of ternaries, mismatch of quaternaries, mis-orientation, layer thickness, tilt, relaxation, indications of strain, curvature and stress, and area homogeneity have important influence on the performance of - and - semiconductors.Ⅲ Ⅴ Ⅱ Ⅵ

MQW laser


12

Material parameter Effect on rocking curve Distinguishing features

Mismatch Splitting of layer andsubstrate peak

Invariant with samplerotation

Mis-orientation Splitting of layer andsubstrate peak

Changes sign with samplerotation

Thickness Affects intensity of peakIntegrated intensityincreases with layerthickness, up to a limit

Thickness Introduces interferencefringes

Fringe period controlled bythickness

Mosaic spread Broadens peakBroadening may increasewith beam size, up tomosaic cell size

Dislocation content Broadens peak Broadening invariant withbeam size

The effect of substrate and epi-layer parameters upon the rocking curve


13

Lattice parameter and composition

Superlattice under full strain (e.g. InxGa1-xAs layer on InP substrate)

θ1

θ2

d`hkl

dhkl

q sin'2 hkld

For zinc blende structure,

For (004) plane,

2 2 2

2 2 2

1 43hkl

h k hk ld a c

4cd

q sin2c

Vegard’s Law:

a1

a2

a c

1(1 )

x xIn Ga As InAs GaAsa xa x a


14

XRD Superlattice period characterization

n

CuK

SLn

1

sin2-sin2

qq

where Λ is the thickness of a SL period, λCuKα1 = 0.15405nm, is the nth-order peak of the MQW, is the zero-order peak.

nqSLq

Λ

θn

nsin2N q

1-nsin21)(N q

Λ

1sin2sin2 1nn

qq

By averaging over the positions of satellite peaks of order n, we got:n according

J.M. Vandenberg, A.T. Macrander, R.A. Hamm, M.B. Panish, Phys. Rev. B 44 (1991) 3991

Outline

15

Introduction XRD





Results and Discussions

16

Sample Structure (not to scale)

S1:• InAlAs• Superlattice x5

• InP• InGaAs

InP (001) InP (001)S2• InAlAs• Superlattice x5

• InP: thickness ~x2• InGaAs: thickness ~x2

InP (001)S3• InAlAs• Superlattice x5

• InGaAs: Same thickness as S2

• InAlAs: Unknown

InxAl1-xAs InPInxGa1-xAs

Outline

17

Introduction XRD






18

XRD Experiments Results

From these curves ,we need to know: • Thickness of InAlAs buffer layer and the period of SL;

• Composition of each material.

With offset

Outline

19

Introduction XRD






20

Peaks belonging

Example to identify peaks from different sources.

InP 600μmInAlAs 135nm


21

Peaks belonging

Zero order peak gives information about

mismatch(composition)

Satel l i te peaks corresponds to

superlatt ice period

InP substrate

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp


22

Peaks belonging

InP substrate

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp

InGaAs

Inp

Repeat of SL period=N+2N=3Repeat=5


23

Peaks belonging

The total curve is the superposition of Layer and SL.InP substrate

InGaAs

InpInGaAs

InpInGaAs

InpInGaAs

InpInGaAs

Inp

InP 600μmInAlAs 135nm


24

Theoretical calculations

n

CuK

SLn

1

sin2-sin2

qq

Red arrow corresponds to fringes produced by InAlAs layer diffraction.

Blue arrow corresponds to nth-order peak by diffraction of SL period

1(1 )


Sample InAlAs thickness SL period

InGaAsInP thickness

composition thickness

S1 117nm 34.2nm 0.577 17.1 nm 17.1 nm

InP (001)



25


For S2, the ideal thickness of SL is twice of that in S1.

According to previous data in S1, multiply by 2 directly.

Blue arrows refer to SL peaks, leading to average period 70 nm;Red arrows refer to Layer peaks, leading to average thickness 126 nm.

Coincidence

Sample Layer_InAlAs SL_InGaAs SL_InP

S2thickness thickness composition thickness

126 nm 34.0 nm 0.572 36.0 nm

1(1 )



InP (001)


26


Arrows: peaks for Layer;Bracket: peaks for SL.

n

CuK

SLn

1

sin2-sin2

qq

Average

Initial values for simulation

Sample Layer_InAlAs SL_InGaAs SL_InAlAs

S3thickness Thickness composition thickness composition

135 nm 34.0 nm 0.556 19.6 nm 0.52

All maximums remain in XRD, indicating that the thickness of two layers in SL are different. Only the total period can be calculated, which is 53.6nm. Besides, the thickness of InGaAs layer is the same as S2, we can take 34.0 nm as initial one ,which can also give that of InAlAs.


InP (001)


27

Simulation and fitting for S1

Sample Layer_InAlAs SL_InP SL_InGaAs

S1thickness composition thickness thickness composition

135 nm 0.5925 17.9 nm 17.0 nm 0.6073

InP (001)



28


Sample Layer_InAlAs SL_InP SL_InGaAs

S2thickness composition thickness thickness composition

132 nm 0.52 36.0 nm 34.5 nm 0.6039

InP (001)



29


Sample Layer_InAlAs SL_InGaAs SL_InAlAs

S3thickness composition thickness composition thickness composition

135 nm 0.52 29.7nm 0.60 21.6nm 0.52

InP (001)



30

Summary

Sample

S1 S2 S3Substrate_InP 600 umLayer_InAlAs 135 nm , In_0.59 132 nm , In_0.52 135 nm , In_0.52

Superlattice

Layer1 InP 17.9 nm InP 36.0 nm InGaAs29.7 nm

In_0.60

Layer2 InGaAs17.0 nm

InGaAs34.5 nm

InAlAs21.6 nm

In_0.60 In_0.60 In_0.52

Outline

31

Introduction XRD





Comparisons with TEM Results

32

137136140

S1 S2 S3

InxAl1-xAs Layer Thickness

137nm 136nm140nm


33

SLs layers thickness

50 nm50 nm50 nm50 nm50 nm

3021

3220

3220

3220

3219

32

134

InP

InAlAs

InGaAs

InGaAs

InGaAs

InGaAs

InGaAs

InAlAs

InAlAs

InAlAs

InAlAs

InGaAsInAlAs


136

3338

3338

3438

3338

3733

InP

InAlAs

InPInGaAs

InGaAs

InGaAs

InGaAs

InGaAs

InP

InP

InP

InP


InAlAs

InPInGaAs

InGaAs

InGaAs

InGaAs

InGaAs

InP

InP

InP

InP16.0

18.516.5

18.016.0

18.516.0

18.516.0

16.5

S1 S2 S3

InGaAs 16nmInP 18nm

InGaAs 33nmInP 38nm

InGaAs 32nmInAlAs 20nm


34

ComparisonSample Part Material XRD TEM Difference

S1

Layer InAlAs 135 nm 137 nm -2nm

SL

InP 17.9 nm 18.0 nm -0.1nm

InGaAs17.0 nm 16.0 nm +1nm

0,60 NA NA

S2


SL

InP 36.0 nm 38.0 nm -2nm

InGaAs34.5 nm 33.0 nm +1.5nm

0.60 NA NA

S3


SL

InGaAs29.7 nm 32.0 nm -2.3nm

0.60 NA NA

InAlAs21.6 nm 20.0 nm +1.6nm

0.52 NA NA

Outline

35

Introduction XRD





Conclusion

36

• XRD studies on superlattice samples with different compositions and periods.

• Based on the information derived from XRD rocking curves, three models were established and simulated.

• The fitting results of all three models not only gave information which TEM could not, but also corresponded well with data already given by TEM figures, indicating the reliability and accuracy of XRD measurement in superlattice structures.

• With its non-destructive property and high efficiency in conducting experiments and results derivation, XRD will be a more suitable method for superlattice researches in many fields.

37

Xiangyu WuEnlong Liu

Thank you !

x-ray diffraction analysis of Ⅲ-Ⅴ superlattices : characterization, simulation and fitting

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