optical properties of infrared emission quaternary ingaasp epilayers y. c. lee a,b, j. l. shen a,...

Optical properties of infrared emission

quaternary InGaAsP epilayers

Y. C. Lee a,b,

J. L. Shena, and W. Y. Uen b

a. Department of Computer Science and Information Engineering,

Tung Nan Institute of Technology, Taipei, Taiwan, R.O.C.

b. Department of Physics, Chung Yuan Christian University

c. Department of electronic, Chung Yuan Christian University

• Long wavelength (1.3 ~1.55μm) emission quaternary InGaAsP semiconductor have been studied extensively because of their potential application to optical fiber communication system.

• The growth methods of InGaAsP layers: a. MBE (molecular beam epitaxy) b. LPE (liquid phase epitaxy)

Introduction

Introduce to MBE

molecularsource

shutter

Substrate

Buffer

Introduce to LPE

IntroductionLiquid Phase Epitaxy ( LPE ) growth process has the unintentional residual impurity from the melt, substrate, source materials and growth ambient.

Doping rare-earth elements into semiconductor is the interest method to reduce the residual impurities (S, Se, Si, C, Te, O, etc.) in the LPE growth.

Optoelectronic Lab.Optoelectronic Lab.

Introduction

The rare-earth elements as the gettering agent have been reduce the impurities which as donors in semiconductor.

The rare-earth elements are insoluble in the solvent used in LPE growth and they are not incorporated into the grown epitaxial layer.


Introduction

There have been many reports describing the effects of the rare-earth doping on semiconductors with Er, Yb, and Gd elements but few describing about Ho.

In this work, we present the influence of Ho and Nd elements doped into quaternary InGaAsP layers by the PL 、 PC 、 CER and Raman measurements.


Samples Profile

InGaAsP Ho-doped (wt%)

undoped 0

Ho 0.017

Ho 0.025

Ho 0.075

Ho 0.110

Ho 0.150


Photoluminescence Measurement


Monochromator

Photoluminescence

K-SpaceK-Space

C.B.C.B.

V.B.V.B.

luminescenceLaser (E > Eg)

electron

recombinationelectron

hole

electron

Results and Discussion

12 K PL spectra of LPE-grown InGaAsP layers as a function of doping amount of the Ho elements:

(a) undoped

(b) 0.017 wt %

(c) 0.025 wt %

(d) 0.075 wt %

(e) 0.110 wt %

(f) 0.150 wt %



0.00 0.03 0.06 0.09 0.12 0.157

8

9

10

11

12

13

14

15

FW

HM

(m

eV)

Ho-content (wt %)

The FWHM of the photoluminescence extracted as a function of the doping amounts of the Ho element.


Larger lattice mismat

ch

[M. C. Wu,J. Appl. Phys71,456 (1992)]

Photoconductivity Measurement


1.0 1.1 1.2 1.3

Inte

nsi

ty (

arb

. un

its)

Energy (eV)

12K Undoped PL PC



1.0 1.1 1.2 1.3

Inte

nsi

ty (

arb

. un

its)

Energy (eV)



Band tail

Theroy

Three main possible mechanisms

For explaining the band tail

1. Phonon-assisted transition: The slop of the band edge is not strong dependent on the temperature.

2. Alloy disorder: With the evaluation of asymmetric broadening of Raman signals, the alloy disorder does not change owing to the Ho doping.

3. Impurity disorder: From the above argument, We suggest that the impurity are responsible for the presence of the Urbach tail in our samples.



1.0 1.1 1.2

PC

inte

nsi

ty (

a.u

.)

Wavelength(nm)

PC-Undoped sample Urbach expression

Urbach expreesion:

α= α0 exp (hν/E0 )

α ： the absorption coefficient

α0 ： constant

E0 ： the Urbach energy

[F. Urbach, Phys. Rev. 92, 1324 (1953)]


The value of E0 which represents the distribution of the tail states extending into the band gap and can be correlated with impurity concentrations on the sample.


The PC spectra of the Ho-doped sample as a function of the doping amount of the Ho elements:

(a) undoped

(b) 0.017 wt %

(c) 0.025 wt %

(d) 0.075 wt %

(e) 0.110 wt %

(f) 0.150 wt%

The open circles show the fit to the absorption tail.



0.00 0.03 0.06 0.09 0.12 0.152

4

6

8

10

12

14

16E

0 (m

eV)

Ho-content (wt %)

The values of Urbach energy E0 as a function of Ho wt %.



Peak position FWHM Urbach energy(eV) (meV) E0 (meV)

undoped 1.1405 14.8 15.570.017 1.1404 9.87 3.980.025 1.139 9.32 3.930.075 1.1411 8.02 3.580.110 1.1405 7.93 3.580.150 1.1408 13.02 10.89

PL PCInGaAsPHo-doped

(wt%)

Values of PL FWHM and Urbach energies of InGaAsP layers with various amount of Ho elements


Contactless Electronrefelectanc Measurement


Third-derivative Functional Fit Third-derivative Functional Fit (TDFF)(TDFF)

0emiR

R Ce E E iR

E : the incident photon energy Eo : the interband transition energy

Γ : the broadening parameter C : the amplitude θ : the phase m : 2.5 for bulk materials



14-K CER spectra of InGaAsP epilayers as a function of doping amount of the Ho elements:

(a) undoped

(b) 0.017 wt %

(c) 0.075 wt %

(d) 0.110 wt %

(e) 0.150 wt %.

The open circles are fits to a TDFF model.


InGaAsPHo-doped

(wt%)

undoped 1.145 22 128.6

0.017 1.138 9 245

0.074 1.14 7 223.2

0.11 1.138 10 236.9

0.15 1.141 12 275.3

Phaseθ

Broadeningparameter

(meV)

E0

(eV)

Values of interband transition, broadening parameter, phase in the fitting of CER lineshapes


Micro-Raman measurement

Monochromator



[ P.Parayanthal and Fred H. Pollak,Phys. Rev. Lett. 52,1822 (1983) ]

The Raman peaks have an asymmetric lineshape, which can be analyzed by a spatial correlation (SC) model.

The alloying or any imperfection in semiconductors may destroy the configurational symmetry and break down the q= 0 momentum selection rule. The spatial correlation function of phonon hence become finite and the Raman spectrum reveals an asymmetric line shape (Γa>Γb).

Results and DiscussionThe Raman peak (InAs-like LO mode) have an asymmetric line shape, which can be fitted by ：

The asymmetric ratio (Γa/Γb) as a functi

on of Ho amounts are almost unchanged the alloy disorder or the structural imperfection in InGaAsP layers is not affected by the Ho doping 200 210 220 230 240 250 260

(e)

(d)

(c)

(b)

(a)

Ram

an I

nte

nsi

ty (

a. u

.)

Raman shift (cm¡Ð1)

2 2

32

2 0

exp4

2

q L

I d q

q

aqBAAq cos122

Conclusion ( )Ⅰ

1. The FWHM of PL peak has been found to reduce as the doping of Ho elements increases from 0 to 0.11 wt %. The narrowest value of the FWHM of PL peak is 7.93 meV with Ho of 0.11 wt%, which is smaller by about 46 % than that of the undoped InGaAsP and better than previous reports on similar composition layers.

2. It is found that the Urbach energy decreases as the Ho doping increases except the sample with 0.1502 wt% Ho-doped, indicating the Ho doping leads to the decrease of impurity concentrations.

Published in Solid-State Commun. 120, 501 (2001)

3. The broadening parameter of contactless electrorefelectasnce spectra has been found to decrease as a function of the Ho-doped increased.

4. We demonstrate that the rare-earth element can be an efficient gettering agent for LPE-grown InGaAsP layers and improves the quality of LPE-grown epilayers.

Conclusion ( )Ⅱ

Published in Phys. Stat. Sol. (a) 200, 439 (2003)

Conclusion ( )Ⅲ1. The Raman line shapes of the Ho-doped InGaAsP epil

ayers are asymmetric. Based on the spatial correlation model, it is found the asymmetric ratio and correlation length of the Raman signals are not influenced by the rare-earth doping.

2. This result suggests that no large amounts of the rare-earth elements are incorporated into the epilayers during purification although the residual impurities can be greatly reduced.


Published in Solid-State Commun. 129, 47 (2004)

optical properties of infrared emission quaternary ingaasp epilayers y. c. lee a,b, j. l. shen a,...

Documents

lpe slide

discussion slide

mbe slide

monochromator slide

band tail theroy slide

rareearth elements

ho elements

rareearth doping