Decorrelation of the Light-emitting-Diode

Internal-quantum-Efficiency Components

Studies of the Electron-hole Concentration-ratio at the Active-region Edge

Dinh Chuong Nguyen

1,2

, David Vaufrey

1,2

and Mathieu Leroux

Univ. Grenoble Alpes, F-38000, Grenoble, France

CEA, LETI, MINATEC Campus, F-38054, Grenoble, France

CNRS – Centre de recherche sur l’Hétéro-Epitaxie et ses Applications (CRHEA),

Rue Bernard Grégory, 06560, Valbonne, France

1 RESEARCH PROBLEM

GaN-based light-emitting diodes (LEDs) have

strongly emerged, especially since the last decade, as

a very promising white-light source, enabling them

to enter many lighting applications and even further.

Those applications mostly required the LEDs to

function at a high-current regime. However, LEDs

still suffer a critical internal-quantum-efficiency

(IQE) loss, known as “droop”. Their IQE falls

drastically at high current-injection after reaching a

peak value at usually relatively low current-densities

(Krames et al., 2007; Morkoç, 2008), degrading the

radiative-recombination rate and the output power

(Cabalu et al., 2006; M.-H. Kim et al., 2007), a

behavior that can be described as a sublinear

increase in light-emission intensity with increasing

diode current-density. The efficiency droop was first

observed in GaN-based LEDs by (Krames et al.,

2000) and (Mukai et al., 1999). The loss’ main

mechanism still remains an important topic that has

raised intense debate by many reasons.

First, the knowledge about the wurtzite GaN is

not complete as several parameters still suffer from

uncertainty, such as the recombination coefficients

or the carrier mobility. The Auger-recombination

coefficients obtained from numerical calculations

and curve-fitting can largely differ from each other,

even though it is related to one of the widely-

accepted droop-inducing processes. The carrier-

mobility variation in GaN is noticed to be different

from that in the well-understood Si, yet only one

model for electron mobility was proposed (Turin,

2005).

Second, though theoretically explained, the

internal mechanisms, especially the recombination,

cannot be separately evaluated by characterization,

or at least in an easy way. Their discrimination is

critical as they can replace each other as the main

loss-inducing mechanism in respect to the LED

functioning-regimes. It has been attempted several

times but the results are still under discussion.

The aforementioned difficulties hinder the droop

reducing but the research activities are still ongoing.

However, in addition to the applied methods, it may

be suggested that new approaches be proposed.

2 OUTLINE OF OBJECTIVES

The LED efficiency-loss being complicated and

involving many different mechanisms that cannot be

easily and separately studied, this PhD. thesis thus

aims to contribute to the decorrelation of these

different droop-inducing factors. It mainly focuses

on the ratio between the electron and hole

concentrations that are injected into the active region

of an LED and contribute to light emission.

Nonetheless, other non-radiative recombination

processes are also taken into account.

This work consists in two parts: LED modeling

and characterizing. The samples are mostly

commercial LEDs but can also be provided by

internal research-projects. Initially, the modeling is

expected to provide an insight into the LED internal-

mechanisms in order to evaluate the impact of each

mechanism on the efficiency loss. The

understanding of those impacts’ degree could help

design a more innovative LED structure in which the

mechanisms favorable to the LED lighting-function

are intensified and the loss-inducing ones are

reduced. The characterization allows to verify the

hypothesis deduced from the simulation.

However, a simulation can also be carried out

based on characterization results since the efficiency

on several internal-project-LEDs can show a strong

improvement without its reasons being clearly

explained.

Nguyen D., Vaufrey D. and Leroux M..

Decorrelation of the Light-emitting-Diode Internal-quantum-Efﬁciency Components - Studies of the Electron-hole Concentration-ratio at the Active-region

Edge.

 2015 SCITEPRESS (Science and Technology Publications, Lda.)

Based on the acquired knowledge from modeling

and characterization, as stated above, more-

innovative high-power LED structures are expected

to be designed.

3 STATE OF THE ART

Many groups have proposed different mechanisms

that they judge to be the main reason of the LED

droop. Those mechanisms are very diverse but as

until 2014, two mainstream processes remain most

relevant to the IQE droop.

On the one hand, (Hader et al., 2008) have

simulated the magnitude of direct Auger-

recombination in the (AlGaIn)N material system and

concluded that Auger losses are too small to account

for the droop. Meanwhile, by taking phonon-assisted

Auger-recombination into account, (Kioupakis et al.,

2011) were able to obtain higher Auger-coefficient

values which are in good agreement with the

experiments (Galler et al., 2012). (Delaney et al.,

2009) have computed the Auger coefficient by the

first-principles density-functional and reported

values that can be as large as 2 × 10

–30

–1

when

the bandgap is approximately 2.5 eV, enabling the

Auger processes to be the main cause of the droop.

However, this coefficient is significantly reduced as

the band gap is higher or lower than 2.5 eV. (Iveland

et al., 2013) have gone further by directly measuring

the Auger-induced electrons from an LED under

electrical injection and concluded that the Auger

processes are the origin of the droop phenomenon.

Comments upon their results were given by

(Bertazzi et al., 2013).

On the other hand, by comparing the optical and

electrical properties of AlGaInN-barrier-enhanced

LEDs with those of GaN-barrier-enhanced LEDs,

(Schubert et al., 2008) suggested that carrier leakage

might be the dominant cause of the efficiency droop.

Through experiments and simulation of the

polarization-field-enhanced carrier-leakage, (M.-H.

Kim et al., 2007) also strengthened this assumption.

Other works based on electron leakage enhanced by

high internal piezoelectric fields were published

elsewhere (Rozhansky and Zakheim, 2007; Schubert

et al., 2007; Xu et al., 2009). It was also suggested

that poor hole-injection may reduce the efficiency

(David et al., 2008; Ni et al., 2008; Zhang et al.,

2014).

Apart from these two main schools of thought,

several groups have indicated other different

mechanisms that may lead to the LED efficiency-

droop, including recombination at dislocation

(Hangleiter et al., 2005), self-heating as the current

increases (Cao and Arthur, 2004). Recently, (Huang

et al., 2013) reported the effect of the lateral current-

spreading on the efficiency droop in a conventional-

chip LED. Studies on current spreading in vertical

LEDs were also carried out (Li and Wu, 2012; Son

et al., 2012). In this paper, the mentioned samples

and simulation models are both vertical-thin-film

(VTF) LEDs. A VTF LED structure is flipped from

the conventional epitaxial stack, with an n-type layer

under a p-type layer and the cathode facing the

anode. The experimental results and the

corresponding simulations will be reported and show

that the efficiency droop in VTF GaN-based LEDs is

partly tuned by spreading.

4 METHODOLOGY

As the semiconductor-device simulation is mainly

numerical, the initial approach is to build a model

for GaN-based LEDs by analytically solving the

mathematical expressions. These expressions are

interconnected and solving them involves the use of

special functions; hence analytical solutions can

hardly be obtained.

Another approach was then carried out. Since the

current passing through an LED mainly consists in

electrons due to their low effective-mass and high

mobility, while the amount of emitted-light is tuned

by the holes as they are minority carriers, the

electroluminescence characterization can provide an

estimation of the ratio between these carriers.

Furthermore, through pulsed-electroluminescence

characterizations, their injection efficiencies can be

evaluated due to the difference in mobility.

Consequently, a pulsed-electroluminescence setup

was realized. The recorded data were later processed

and compared to the simulation results in a

following communication.

As for the modeling, the ATLAS package from

SILVACO Corporation is utilized. The carrier

concentration is calculated with special attention,

especially at the edges of the active region, because

their enhancing or limiting role will become clear at

these positions. The simulation can be coupled with

characterization whether to verify the modeling

accuracy or to explain the measurements. The work

presented later in this paper was based on the

characterization results from two different LED-

structures. The simulation was later carried out to

partly explain the observed changes between the two

structures. Deeper studies on the carrier

concentrations followed and provided an insight into

PHOTOPTICS2015-DoctoralConsortium

the unbalanced distributions of electrons and holes

entering the active region, where they might

eventually recombine. This observation then

suggested that the p-type layer play an important

role in the carrier transport and lead to the p-GaN-

properties studies through characterization.

5 EXPECTED OUTCOME

The electroluminescence measurements show a time

shift between the onset of the current signal and that

of the luminous signal. This shift is expected to

represent the different degrees of carrier-injection

efficiency if it varies with regard to the material

parameters. The data processing was still ongoing

when this article was being written.

The studies on the p-GaN properties could

provide additional information needed to better

understand the carrier behaviors and their impact on

the efficiency loss. They can help complete the

modeling and eventually establish the ratio between

the electron and the hole concentrations, hence this

ratio’s weight in the IQE droop can hopefully be

estimated. Sample preparations are expected to be

finished shortly.

If these goals are achieved, by the end of this

PhD. thesis, new ideas for a more efficient LED-

design might be proposed.

6 STAGE OF THE RESEARCH

In this paper, the work carried out through modeling

will be presented. Its results will be applied in the

incoming works.

This work started from the characterization

results obtained on a project’s samples, followed by

the ATLAS software package simulation.

6.1 Sample Structure and Simulation

Model

Two sample structures were fabricated, electrically

and optically characterized. Those are square

900 µm × 900 µm LEDs, differing from each other

only in their cathode. The first structure, hereby

called LED 1, has a round 100-µm-diameter

cathode, situated in the middle of its surface. The

second structure, LED 2, has multiple-stripe-like

cathodes that are parallel to each other. These two

structures were modeled as described below with the

same parameters. Though the structure used to

model the LED 1 does not possess a round cathode,

its section should resemble that of the LED 1.

To simulate the aforementioned LED 1 and

LED 2, two vertical GaN-based LED structures with

different-shaped cathodes are modeled: the LED A

has a single-striped cathode that is placed in the

middle of the p-type surface, while the LED B has

nine striped-cathodes that are parallel to each other.

Their widths are also 900 µm. In the LED A, the

cathode width is set to 225 µm. The cathodes in the

LED B are 25 µm-wide and separated from each

other at a distance of 75 µm. Consequently, in both

structures, the total area covered by the cathodes is

equivalent. The p-type layer is 3-µm-thick and the

ionized-acceptor concentration is 5 × 10

–3

. The

n-type-layer thickness and ionized-donor

concentration are respectively kept at 3 µm and

5 × 10

–3

. All the doping profiles are uniform.

Both structures also consist of five 3-nm-thick

undoped In

0.1

0.9

N quantum wells, separated by

four 10-nm-thick GaN barriers. However, neither of

them consists of an electron-blocking layer (EBL).

The anode covers the full surface of the LED

structures. Both the anode and cathode are

considered to be ohmic contacts. The section of one-

half of the LED A is shown in Figure 1(a) and the

section of one-third of the LED B is shown in Figure

1(b). Note that they are not in exact scale.

As stated before, the simulations were carried out

on the ATLAS software package by SILVACO

Corporation. Standard Shockley-Read-Hall (SRH),

Auger and three-band radiative-recombination

models are used to respectively simulate the non-

radiative and radiative mechanisms. For the SRH

model, the electron and hole lifetimes are both fixed

at 100 ns. This value is high compared to those

reported in the state of the art but approximate to

those reported by (Delaney et al., 2009) and will

reduce the SRH-recombination rate. Meanwhile, the

trap energy level for this recombination is situated in

the middle of the band gap, meaning that the highest

possible SRH-recombination rate is computed. The

electron and hole Auger-coefficients are set to be

–30

–1

, a larger value than the usually reported

ones in the state of the art in order to enhance Auger

recombination. The built-in electric charges

occurring at the p-n interface due to spontaneous and

piezoelectric polarization were also calculated. Its

theoretical value is usually reduced due to screening

effects, but the extent of this reduction is still

uncertain (Della Sala et al., 1999; Piprek et al., 2006;

Romanowski et al., 2010). Hence, in our simulation,

the final polarization charge density is assumed to be

80% of the theoretical value. The defect-related loss

DecorrelationoftheLight-emitting-DiodeInternal-quantum-EfficiencyComponents-StudiesoftheElectron-hole

Concentration-ratioattheActive-regionEdge

was not taken into account during the simulation and

the temperature is kept at 300 K.

Several other assumptions were made to simplify

the simulations. The electron and hole mobility are

respectively 400 cm

/Vs and 8 cm

/Vs. However, in

the InGaN quantum wells, they are both 100 cm

/Vs.

All these values are suggested by ATLAS. They are

kept constant throughout the simulation for two

main reasons. The first one is to lighten the model.

The second one is the lack of empirical models for

electron and hole mobility, especially under the

effect of a high electric field, except the model

proposed by (Turin, 2005). That being said, at high

injection currents, the modeled LED-behaviors will

deviate from the common experimental

characteristics.

In order to simulate the light output, the

radiative-recombination rate is only integrated over

the areas that are not shaded by the cathodes.

6.2 Experimental Results

The experimental results obtained on a set of

samples are plotted in Figure 2. It can be clearly

seen in Figure 2(a) that the IQE and especially its

peak-value are higher in the LED 2 than in the

LED 1. Moreover the current density corresponding

to this peak value is also higher in the LED 2 than in

the LED 1, shifted to approximatively 15 A/cm

instead of 10 A/cm

Furthermore, Figure 2(b) displays the normalized

IQE from the two LEDs. The droop is more

significant in the LED 1 than in the LED 2, with

efficiency falling to less than 40 % of the peak value

at 100 A/cm

. The forward-current density and the

optical-power density of the LED 2 also respectively

exceed those of the LED 1, as shown on Figure 2(c)

and Figure 2(d). These results imply that by

replacing a round cathode by a multiple-arrayed

cathode, the LED performance can be critically

enhanced and the droop reduced. To further

understand this difference, the next sections will

discuss the simulation results for the LEDs A and B

which are representative for the LEDs 1 and 2,

respectively.

6.3 Studies by Modeling

6.3.1 Current-spreading Analysis

Due to the multiple-stripe-like cathode-geometry,

current spreading certainly occurs in the LED

structure. The current spreading length was shown to

depend on the forward voltage and for GaN-based

LEDs, the Thompson spreading-current model was

demonstrated to be more appropriate than the Guo-

Schubert model (H. Kim et al., 2007). Since the

stripe-like electrodes in our experiments are located

on a thick n-type layer, the current is more likely to

totally spread throughout the n-type layer before

entering the p-type layer. Thus, the current-

spreading is mainly considered to occur in the n-

layer and its length was calculated for the two LEDs

A and B by the Thompson model (Thompson, 1980)

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

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







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(1)

Figure 1: (a) One-half of the LED A; (b) One-third of the LED B with three cathodes. The material parameters are the same

in both structures; hence they are displayed in only one of the structures.

PHOTOPTICS2015-DoctoralConsortium

Figure 2: The experimental results from the LED 1 (black solid line) and the LED 2 (blue solid line), respectively a)

Efficiency, b) Normalized efficiency, c) J-V characteristic curve and d) L-V curve.

where n, k

, T, t

, q, ρ

are respectively the ideality

factor, the Boltzmann constant, the temperature, the

n-layer thickness, the elementary charge and the n-

layer resistivity. J

is the current density at the edge

of the contact. The current density J(x) extending

away from the contact is given by

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

(2)

can be approximated as the uniform current-

density under the cathodes, which can be measured

from the simulation. The n-type layer resistivity was

approximated by 











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



and the ideality

factor was extracted from the simulated J-V curve as

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equation Error! Reference source not found., this

gives

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An integral of the equation (2) from the edge of the

contact to a position t gives

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



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









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(4)

which represents the electric-current intensity per

unit length covering from the contact edge to the

position t. By multiplying it by the number of the

unshaded areas in the LEDs A and B, one obtains

the current intensity per unit length in the whole part

of the LED where light extraction is not hindered by

the opaque cathodes. The formula (4) also suggests

that a higher current-injection is more likely

achieved when the distance t is lower than L

The calculations indeed indicate that the LED B

with the multiple-striped cathodes injects a higher

current intensity than the LED A with the single-

striped cathode. However, this information still

cannot fully explain the shift of the IQE peak and

the IQE increase. As shown by Figure 3, the IQE of

the LED B at a certain current density can remain

higher than that of the LED A at a lower current

density while intuitively the IQE should decrease as

the current density increases. An insight into the IQE

is then needed and presented in the next section.

6.3.2 Internal-quantum-Efficiency and

Carrier-concentration Profile

Figure 3 shows the calculated internal quantum

efficiency (IQE) from the two LEDs. It can be seen

that the highest IQE value from the LED B is larger

than that of the LED A, reaching nearly 70 %. The

current density corresponding to this peak value is

approximately 6 A/cm

, also exceeding that of the

0 20 40 60 80 100

0.2

0.4

0.6

0.8

Current Density (A/cm

)

IQE (Arbitrary Unit)

(a) IQE

LED 1

LED 2

0 1 2 3 4

-5

Voltage (V)

Current Density (A/cm

)

LED 1

LED 2

0 20 40 60 80 100

0.2

0.4

0.6

0.8

Current Density (A/cm

)

Normalized IQE

(b) Normalized IQE

LED 1

LED 2

0 1 2 3 4

-4

-2

(d) Optical Power Density

Voltage (V)

Optical Power Density (W/cm

)

LED 1

LED 2

DecorrelationoftheLight-emitting-DiodeInternal-quantum-EfficiencyComponents-StudiesoftheElectron-hole

Concentration-ratioattheActive-regionEdge

LED A. Moreover, after reaching their peak values,

while the IQE of the LED A is drastically reduced as

the current density rises, the IQE of the LED B

slowly decreases with the current density.

One reason leading to such a difference might be

the lower hole injection into the unshaded parts of

the active layer in the LED A. Thus, the charge-

carrier profile at the interface between the p-GaN

layer and the MQW region was investigated and is

shown in Figure 4. This profile is taken at a higher

voltage than the one corresponding to the IQE peak

value. In such situation, the space-charge-region

(SCR) width becomes extremely small and the

region’s edges move towards the interfaces of the

MQW region. The hole concentration at the

interface p-layer/MQW can be considered

proportional to the hole-current density.

The hole-concentration profile at the interface is

represented by the curve, while the parts

corresponding to the unshaded areas are marked by

the color. They clearly show that the hole

concentration in the areas situated right below the

cathodes (blank areas) is significantly higher than

that in the other areas. This phenomenon can be

explained by the fact that the areas shaded by the

cathodes benefit from a direct hole-injection under

the influence of a strong electric field, whereas in

the unshaded areas the injected-hole concentration is

only slightly raised by the spreading phenomenon.

At this interface, the electric field due to the lattice

mismatch between the p-GaN layer and the InGaN

quantum well and the spontaneous polarization of

GaN altogether hinder the hole injection into the

active region. The strong electric field under the

shaded area reduces this polarization-induced field

better than that in the unshaded areas. This fact also

implies that a large part of the luminous intensity is

lost because the radiative-recombination must be

strongest in those shaded areas.

The average hole concentration in the unshaded

areas is higher in the multiple-cathode LED B than

in the single-cathode LED A. Indeed, at this

interface, the average hole-concentration in the

unshaded areas is 1.72 × 10

–3

in the LED A and

1.23 × 10

–3

in the LED B, meaning that the hole

injection is more efficient in the LED B.

Furthermore, the average electric-field intensity in

those unshaded parts of the interface is directed

towards the p-GaN layer with values of 66 kV/cm

and 25 kV/cm in the LED A and the LED B

respectively. Consequently, the hole transport is

further hampered in the LED A than in the LED B,

resulting in a lower hole concentration in the active

area.

Figure 3: The simulation results from the LED A (black solid line) and the LED B (blue solid line), respectively a)

Efficiency, b) Normalized efficiency, c) J-V characteristic curve and d) L-V curve.

0 10 20 30 40 50

0.2

0.4

0.6

0.8

Current Density (A/cm

)

IQE (Arbitrary Unit)

(a) IQE

LED A

LED B

0 10 20 30 40 50

0.2

0.4

0.6

0.8

Current Density (A/cm

)

Normalized IQE

(b) Normalized IQE

LED A

LED B

0 1 2 3 4

Voltage (V)

Current Density (A/cm

)

LED A

LED B

0 1 2 3 4

Voltage (V)

Optical Power Density (W/cm

)

(d) Optical Power Density

LED A

LED B

PHOTOPTICS2015-DoctoralConsortium

At the interface between the n-type layer and the

MQW region, the electron-concentration profile (not

shown here) resembles to the above-mentioned hole-

concentration. The average electron-concentrations

in the unshaded areas are respectively

0.76 × 10

–3

and 2.62 × 10

–3

in the LED A

and the LED B. However, the average electric-field

intensities are approximately equivalent:

5.4 × 10

V/cm in LED A and 5.9 × 10

V/cm in

LED B.

The injected-hole concentration in the LED B is

more than seven times higher than that in the

LED A, while the same ratio for the injected-

electron concentration between these LEDs is

approximately 3.5. Thus, we suspect that the p-type

layer plays a major role in LED current-injection

and particularly in balancing the charge ratio.

Moreover, as shown by Figure 5, the local injected-

electron/injected-hole ratio is much higher in the

LED A than in the LED B, even reaching values as

high as 45 at the structure’s edges. This ratio in the

LED B consistently fluctuates at around 2,

suggesting that the carrier concentration profile

tends towards an equilibrium which may reduce the

unbalanced charge-ratio and consequently the carrier

leakage. Such values are remarkable as both

structures do not have any electron-blocking layer

and the ionized-donor concentration in the n-type

layer is higher than the ionized-acceptor

concentration in the p-type layer. Furthermore, this

local ratio increases as the distance from the contact

edge increases, while the carrier concentration and

the local current-density decrease. This observation

implies that in this type of LED structure, the

electrode spacing is critical since if it is not well

implemented it can induce areas where poor and

unbalanced carrier-injection occurs. This

problematic should be very critical in the

conventional-chip structure where the mesa length

must be taken into account during LED design, as

remarked by (Huang et al., 2013).

6.4 Overview

Experimental measurements and simulations on

LEDs with two different cathode-structures have

been realized. The characterization and simulation

results show a strong correlation and demonstrate an

improvement in the LED internal-quantum-

efficiency by optimizing the current injection into

the active region. This injection optimization is

critical in LED design as it affects the injected-

carrier concentration-ratio at the active-region edges

and in respect of this ratio variation, the carrier

leakage can be either reduced or intensified. The

simulations also indicate an important role of the

LED p-type-layer in the current injection and,

consequently, in the IQE droop. The employment of

the multiple-stripe-like cathode-structure slightly

varies the electron injection and the electric field

from the n-side of the active region, but strongly

modulates those from the p-side. These unbalanced

injection-induced influences tend to imply a major

Figure 4: Hole-concentration profile at the p-layer/MQW-region interface (left: LED A, right: LED B) at a voltage higher

than that corresponding to the peak IQE value. It implies that the total colored-surface is higher in the LED B than in the

LED A.

0 200 400 600 800

14.5

15.5

16.5

Position (µm)

log

(hole concentration) (cm

-3

)

LED B

0 200 400 600 800

14.5

15.5

16.5

Position (µm)

log

(hole concentration) (cm

-3

)

LED A

DecorrelationoftheLight-emitting-DiodeInternal-quantum-EfficiencyComponents-StudiesoftheElectron-hole

Concentration-ratioattheActive-regionEdge

Figure 5: The local injected-electron/injected-hole into the active region at a voltage higher than that corresponding to the

peak IQE for the LED A (left) and the LED B (right). The LED A shows a much more unbalanced local-carrier-profile-ratio

than the LED B and is seemingly more prone to the carrier leakage.

impact of the carrier leakage and perhaps a lesser

role of the Auger-recombination processes in the

IQE droop of LEDs without electron-blocking layer.

It should be noted that, as stated at the beginning, in

the simulations, the SRH carrier-lifetime and the

Auger coefficient were intentionally chosen in order

for the SRH-recombination rate to be reduced and

for the Auger-recombination rate to be amplified.

Several recent results (not detailed in this paper)

suggested that the IQE curve and peak do not

coincide with those of the radiative-recombination-

percentage curve. The latter represents the

percentage of the radiative-recombination rate in the

total recombination rate. In addition to the difference

between the electron and hole concentrations at the

edges of the active region, this impact from carrier

leakage may imply that the commonly-used ABC-

model should be applied very carefully to LEDs

without any electron-blocking layer as it usually

assumes that electron and hole concentrations are

equivalent at high injection.

6.5 Perspective

As stated in the previous section, the p-GaN layer

may play a major role in the efficiency loss. To

further understand the p-type-layer impact on the

carrier injection, further experiments are needed to

study its carrier transport properties. Those

properties are expected to be characterized with

respect to the GaN polarity by using several specific

sample-designs. Important parameters such as the

temperature and the electric field will be varied

during the measurements.

Apart from the material characterization, the

pulsed electroluminescence will help establish the

injected-carrier ratio inside an LED under an

electrical excitation. As seen from the simulation

results, this ratio is expected to be unbalanced,

especially in LEDs without any electron-blocking-

layer. The data acquisition is still ongoing and will

soon be followed by the data-processing phase.

The obtained results are expected to be

communicated soon and contribute to the

decorrelation of the IQE components.

ACKNOWLEDGMENT

This PhD. thesis is funded by the optoelectronic

department (LETI/DOPT) of CEA Grenoble

research center. The author is grateful to the

CNRS/CRHEA for the provided samples.

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