Semiconductor devices - Part 5-12: Optoelectronic devices - Light emitting diodes - Test method of LED efficiencies

IEC TR 60747-5-12:2021(E) discusses the terminology and the measuring methods of optoelectronic efficiencies of single light emitting diode (LED) chip or package without phosphor. White LEDs for lighting applications are out of the scope of this part.
This technical report provides guidance on
- terminology of optoelectronic efficiencies of single LED chip or package without phosphor, such as the power efficiency (PE), the external quantum efficiency (EQE), the voltage efficiency (VE), the light extraction efficiency (LEE), the internal quantum efficiency (IQE), the injection efficiency (IE), and the radiative efficiency (RE);
- test methods of optoelectronic efficiencies of the PE, the EQE, the VE, the LEE, and the IQE;
- review of various IQE measurement methods reported so far in view of accuracy and practical applicability;
- the measuring method of the LED IQE based on the temperature-dependent electroluminescence (TDEL);
- the measuring method of the LED IQE based on the room-temperature reference-point method (RTRM);
- the measuring method of the radiative and nonradiative currents of an LED;
- the relationship between the IQE and the VE, which leads to introduction of a new LED efficiency, the active efficiency (AE) as AE = VE × IQE.

General Information

Status
Published
Publication Date
12-Oct-2021
Current Stage
PPUB - Publication issued
Completion Date
13-Oct-2021
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IEC TR 60747-5-12
Edition 1.0 2021-10
TECHNICAL
REPORT
colour
inside
Semiconductor devices –
Part 5-12: Optoelectronic devices – Light emitting diodes – Test method of LED
efficiencies
IEC TR 60747-5-12:2021-10(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 60747-5-12
Edition 1.0 2021-10
TECHNICAL
REPORT
colour
inside
Semiconductor devices –
Part 5-12: Optoelectronic devices – Light emitting diodes – Test method of LED
efficiencies
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.080.99 ISBN 978-2-8322-1035-9

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 60747-5-12:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative reference ........................................................................................................ 8

3 Terms and definitions ...................................................................................................... 8

3.1 General terms and definitions ................................................................................. 9

3.2 Terms and definitions relating to the optoelectronic efficiencies .............................. 9

3.3 Terms and definitions relating to measuring the efficiencies .................................. 11

3.4 Terms and definitions relating to measuring current components .......................... 12

3.5 Abbreviated terms ................................................................................................. 12

4 LED efficiencies............................................................................................................. 13

4.1 General ................................................................................................................. 13

4.2 Theoretical background of optoelectronic efficiencies ........................................... 15

4.3 Separate measurement of various efficiencies ...................................................... 20

4.4 Requirements for accurate and reliable IQE measurement .................................... 20

4.5 Classification of IQE measurement methods ......................................................... 21

5 Conventional IQE measurement methods: features and limitations ................................ 22

5.1 Calculation of the LEE .......................................................................................... 22

5.2 Temperature-dependent photoluminescence (TDPL) ............................................. 22

5.3 Intensity-dependent photoluminescence (IDPL) or simply photoluminescence

(PL) ...................................................................................................................... 23

5.4 Temperature-dependent time-resolved photoluminescence (TD-TRPL) ................. 26

5.5 Time-resolved photoluminescence (TRPL) ............................................................ 28

5.6 Time-resolved electroluminescence (TREL) .......................................................... 34

5.7 Constant ABC model ............................................................................................. 39

5.8 Constant AB model ............................................................................................... 45

6 Standard IQE measurement method I: TDEL ................................................................. 46

6.1 Temperature-dependent electroluminescence (TDEL) method .............................. 46

6.2 Temperature-dependent radiant power .................................................................. 46

6.3 Evaluation of the IQE ............................................................................................ 47

6.4 Validity of the TDEL: examples of blue LEDs ........................................................ 49

6.5 Sequence of IQE determination by the TDEL ........................................................ 50

6.6 Summary of the TDEL ........................................................................................... 51

7 Standard IQE measurement method II: RTRM ............................................................... 51

7.1 Room-temperature reference-point method (RTRM) .............................................. 51

7.2 Recombination coefficients, A, B, and C in semiconductors ................................... 52

7.3 Strategy of the IQE measurement just at an operating temperature ....................... 53

7.4 Theoretical background of the RTRM .................................................................... 54

7.5 Example of the RTRM ........................................................................................... 56

7.6 Comparison of IQEs by the TDEL and the RTRM .................................................. 59

7.7 Summary of the RTRM .......................................................................................... 60

8 The RTRM versus the TDEL and the constant ABC model: comparisons ....................... 60

9 LED performance issues related to the IQE measurement ............................................. 67

9.1 Various LED efficiency measurement .................................................................... 67

9.2 Radiative and nonradiative currents ...................................................................... 70

9.3 The active efficiency (AE): IQE versus forward voltage ......................................... 74

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IEC TR 60747-5-12:2021 © IEC 2021 – 3 –

10 Conclusion: test method of optoelectronic efficiencies of LEDs ...................................... 80

Bibliography .......................................................................................................................... 81

Figure 1 – Sequence of the efficiency measurements ........................................................... 20

Figure 2 – Theoretical model for analysing the TRPL experiment .......................................... 30

Figure 3 – Schematic TRPL response and its interpretation in terms of various lifetimes ....... 32

Figure 4 – Temporal responses of the TRPL for three samples ............................................. 33

Figure 5 – Fitted results of the measured TRPL response ..................................................... 34

Figure 6 – Schematic diagram of the pulse current injection.................................................. 35

Figure 7 – Square of 1τ as a function of current density for a bias voltage ....................... 39

Figure 8 – Estimated IQE (left axis) and measured EQE (right axis) versus current

density .................................................................................................................................. 39

Figure 9 – Experimental EQE curve of a blue LED ................................................................ 42

Figure 10 – Normalized EQE curves (solid lines) and experimental data (rectangular

symbols) for different IQE peak values as a parameter for a blue LED emitting at

460 nm ................................................................................................................................. 42

Figure 11 – SRH nonradiative carrier lifetime as a function of the C
τA= 1
( )
SRH

coefficient calculated from Equation (82) .............................................................................. 43

Figure 12 – Experimental EQE curve of a blue LED .............................................................. 43

Figure 13 – Temperature characteristics of an LED ............................................................... 47

Figure 14 – IQEs as a function of current at various operating temperatures from room

to cryogenic measured by the TDEL method ......................................................................... 49

Figure 15 – Two different cases of normalized EQE curves as a function of current at

various temperatures ............................................................................................................ 50

Figure 16 – Sequence of the IQE measurement by the TDEL method ................................... 51

Figure 17 – Comparison between the conventional ABC model and the improved AB

model ................................................................................................................................... 54

Figure 18 – Calculation procedure from a relative EQE curve to an IQE curve with the

RTRM ................................................................................................................................... 54

Figure 19 – IQE calculation procedure as a function of current based on the RTRM.............. 57

Figure 20 – Example of the IQE calculation based on the RTRM ........................................... 59

Figure 21 – Comparison of the IQEs evaluated by (a) the TDEL and (b) the RTRM ............... 60

Figure 22 – Radiant power versus current of a blue LED sample measured at various

temperatures ........................................................................................................................ 61

Figure 23 – Normalized intensities on linear and log scales measured at various

temperatures ........................................................................................................................ 62

Figure 24 – I-V characteristics at various temperatures ......................................................... 63

Figure 25 – Calculated a as a function of current for various temperatures. I at

2 ref

300 K is the current giving the minimum value of a in region II. ........................................... 64

Figure 26 – IQEs obtained by the RTRM (symbols) and the TDEL (solid lines) at

various temperatures ............................................................................................................ 64

Figure 27 – Comparison of the IE obtained from a at 300 K (left axis) and the

theoretical IE for constant I (right axis) ........................................................................... 65

leak

Figure 28 – Normalized EQE and the fitting by the constant ABC model ............................... 66

Figure 29 – Ratio of the SRH, radiative, Auger recombination currents to the total

current .................................................................................................................................. 66

---------------------- Page: 5 ----------------------
– 4 – IEC TR 60747-5-12:2021 © IEC 2021

Figure 30 – Radiant power and forward voltage as a function of forward current ................... 68

Figure 31 – Calculation of the mean photon energy from the emission spectra ..................... 69

Figure 32 – LED efficiencies as a function of forward current ............................................... 70

Figure 33 – Sequence of the radiative and nonradiative current measurements .................... 72

Figure 34 – IQE and forward voltage as a function of forward current ................................... 72

Figure 35 – Radiative current and forward voltage as a function of forward current ............... 73

Figure 36 – Nonradiative current and forward voltage as a function of forward current .......... 73

Figure 37 – Total forward current, radiative current, and nonradiative current plotted as

a function of forward voltage ................................................................................................. 74

Figure 38 – Distribution of the IQE and V for 31 blue MQW LEDs ....................................... 76

Figure 39 – Optoelectronic characteristics of three samples under consideration .................. 77

Figure 40 – Separated radiative and nonradiative current densities of samples 1 and 2 ........ 78

Figure 41 – Separated radiative and nonradiative current densities of samples 1 and 3 ........ 79

Table 1 – LED items and their measuring methods listed in IEC 60747-5-6:2016 .................. 14

Table 2 – Summary of efficiency items defined in IEC 60747-5-8:2019 ................................. 19

Table 3 – Various LED IQE measurement methods ............................................................... 22

Table 4 – Parameters in IQE and current density versus voltage curves ............................... 77

Table 5 – Comparison of recombination mechanisms between samples ................................ 79

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IEC TR 60747-5-12:2021 © IEC 2021 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
Part 5-12: Optoelectronic devices – Light emitting diodes –
Test method of LED efficiencies
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC TR 60747-5-12 has been prepared by subcommittee 47E: Discrete semiconductor devices,

of IEC technical committee 47: Semiconductor devices. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
47E/741/DTR 47E/748/RVDTR

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this Technical Report is English.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 60747-5-12:2021 © IEC 2021

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

A list of all parts in the IEC 60747 series, published under the general title Semiconductor

devices, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under webstore.iec.ch in the data related to the

specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it

contains colours which are considered to be useful for the correct understanding of its

contents. Users should therefore print this document using a colour printer.
---------------------- Page: 8 ----------------------
IEC TR 60747-5-12:2021 © IEC 2021 – 7 –
INTRODUCTION
The latest international standards for light emitting diode (LED) devices are

IEC 60747-5-6:2016, IEC 60747-5-8:2019, IEC 60747-5-9:2019, IEC 60747-5-10:2019, and

IEC 60747-5-11:2019, where terminology and measuring methods of basic electrical and optical

characteristics of LEDs are given.

This technical report gives guidance on the terminology and the measuring methods of various

efficiencies of single light emitting diode (LED) chip or package without phosphor. White LEDs

for lighting applications are out of the scope of this part of IEC 60747-5-12.

The efficiencies whose measuring methods are described in this technical report are the power

efficiency (PE), the external quantum efficiency (EQE), the voltage efficiency (VE), the internal

quantum efficiency (IQE), and the light extraction efficiency (LEE). To measure these

efficiencies separately, one needs the measurement data of the internal quantum efficiency

(IQE).

The IQE is a key performance parameter that represents the quality of epitaxial wafers and

contains essential information on operational mechanisms. Requirements for accurate and

reliable IQE measurements are suggested. The various IQE measurement methods reported so

far are reviewed in detail from a theoretical and practical point of view. Subsequently, the

technical limitations for these IQE measurement methods to meet the requirements for accurate

and reliable IQE measurements are discussed.

In particular, two different measuring methods of the IQE that can meet the requirements are

described in detail both experimentally and theoretically. They are known as the temperature-

dependent electroluminescence (TDEL) and the room-temperature reference-point method

(RTRM).

A measuring procedure of PE, EQE, VE, IQE, and LEE are demonstrated. But the injection

efficiency (IE) and the radiative efficiency (RE) are described for definitions only.

Separate knowledge of various efficiencies of the LED chip or package is able to improve

optoelectronic performances of LED chip itself and to design LED application systems such as

LED lamps more efficiently and reliably.
---------------------- Page: 9 ----------------------
– 8 – IEC TR 60747-5-12:2021 © IEC 2021
SEMICONDUCTOR DEVICES –
Part 5-12: Optoelectronic devices – Light emitting diodes –
Test method of LED efficiencies
1 Scope

This technical report discusses the terminology and the measuring methods of optoelectronic

efficiencies of single light emitting diode (LED) chip or package without phosphor. White LEDs

for lighting applications are out of the scope of this part.
This technical report provides guidance on

– terminology of optoelectronic efficiencies of single LED chip or package without phosphor,

such as the power efficiency (PE), the external quantum efficiency (EQE), the voltage

efficiency (VE), the light extraction efficiency (LEE), the internal quantum efficiency (IQE),

the injection efficiency (IE), and the radiative efficiency (RE) [1] ;

– test methods of optoelectronic efficiencies of the PE, the EQE, the VE, the LEE, and the

IQE [1];

– review of various IQE measurement methods reported so far in view of accuracy and

practical applicability;
– the measuring method of the LED IQE based on the temperature-dependent
electroluminescence (TDEL) [2];

– the measuring method of the LED IQE based on the room-temperature reference-point

method (RTRM) [3];
– the measuring method of the radiative and nonradiative currents of an LED [4];

– the relationship between the IQE and the VE, which leads to introduction of a new LED

efficiency, the active efficiency (AE) as AE = VE × IQE.
2 Normative reference

The following document is referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60747-5-6, Semiconductor devices – Part 5-6: Optoelectronic devices – Light emitting

diodes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 10 ----------------------
IEC TR 60747-5-12:2021 © IEC 2021 – 9 –
3.1 General terms and definitions
3.1.1
radiant power
change in radiant energy with time

Note 1 to entry: The unit used is: W. Radiant power is also known as "radiant flux".

[SOURCE: IEC 60050-845:2020, 845-21-038, modified – Note 1 has been expanded.]
3.1.2
spectral distribution
density of a radiant power , with respect to wavelength, λ , at the wavelength λ
dΦλ
( )
Φ =
e,λ

[SOURCE: IEC 60050-845:2020, 845-21-029, modified – In the definition, "a radiant or luminous

or photon quantity X ()λ " has been replaced by "a radiant power Φ ". In the formula, X has

been replaced by Φ . Notes have been deleted.]
3.1.3
mean photon energy
mean energy that each photon carries
hν=
Φ dλ
e,λ
where
h is the Planck constant;
c is the speed of light in vacuum
[SOURCE: IEC 60747-5-8:2019, 3.1.3]
3.2 Terms and definitions relating to the optoelectronic efficiencies
3.2.1
power efficiency

ratio of the radiant power (coupled to free space), , to the electrical power consumed by the

LED, V I , where V is the forward voltage and I is the forward current of the LED

F F F F
η =
F F

Note 1 to entry: Power efficiency is also known as the "wall-plug efficiency". Power efficiency is identical to the

"radiant efficiency" when the power dissipated by any auxiliary equipment is excluded from the electrical power.

---------------------- Page: 11 ----------------------
– 10 – IEC TR 60747-5-12:2021 © IEC 2021
[SOURCE: IEC 60747-5-8:2019, 3.2.1]
3.2.2
voltage efficiency

ratio of the mean photon energy emitted from the LED to the electron energy given by the

forward voltage of the LED, V
η =
where
q is the elementary charge.

Note 1 to entry: Voltage efficiency can be greater than 1 at very low forward currents.

[SOURCE: IEC 60747-5-8:2019, 3.2.2]
3.2.3
external quantum efficiency
EQE

ratio of the number of photons emitted into the free space per unit time to the number of

electrons injected into the LED per unit time
Φ hν
η =
EQE
[SOURCE: IEC 60747-5-8:2019, 3.2.3]
3.2.4
internal quantum efficiency
IQE

ratio of the number of photons emitted from the active region per unit time to the number of

electrons injected into the LED per unit time
Φ hν
e,active
η =
IQE
where
Φ is the radiant power emitted from the active region.
e,active
[SOURCE: IEC 60747-5-8:2019, 3.2.4]
3.2.5
light extraction efficiency
LEE

ratio of the number of photons emitted into the free space to the number of photons emitted

from the active region
---------------------- Page: 12 ----------------------
IEC TR 60747-5-12:2021 © IEC 2021 – 11 –
η =
LEE
e,active
[SOURCE: IEC 60747-5-8:2019, 3.2.5]
3.2.6
injection efficiency

ratio of the number of electrons injected into the active region per unit time to the number of

electrons injected into the LED per unit time
F,active
η =
where
I is the portion of the forward current injected into the active region.
F,active
[SOURCE: IEC 60747-5-8:2019, 3.2.6]
3.2.7
radiative efficiency

ratio of the number of photons emitted from the active region per unit time to the number of

electrons injected into the active region per unit time
Φ hν
e,active
η =
F,active

[SOURCE: IEC 60747-5-8:2019, 3.2.7, modified – The specific use in angle brackets as well as

the note have been removed.]
3.3 Terms and definitions relating to measuring the efficiencies
3.3.1
peak EQE point

set of operating conditions of the forward current and radiant power at which the EQE is the

maximum for a given temperature.

Note 1 to entry: The forward current and radiant power at the peak EQE point are denoted as I and Φ ,

peak peak
respectively.
[SOURCE: IEC 60747-5-9:2019, 3.1.6]
3.3.2
cryogenic temperature
temperature range below 200 K
[SOURCE: IEC 60747-5-9:2019, 3.1.7]
---------------------- Page: 13 ----------------------
– 12 – IEC TR 60747-5-12:2021 © IEC 2021
3.3.3
critical cryogenic temperature
cryogenic temperature at which the peak EQE shows the maximum value
[SOURCE: IEC 60747-5-9:2019, 3.1.9]
3.3.4
normalized variables of X and Y
converted quantities of current and radiant power as follows:
X= Φ I /Φ I
( )
( )
e F e peak
YI= / I
F peak
[SOURCE: IEC 60747-5-10:2019, 3.1.7]
3.3.5
coefficients of a and a
1 2
coefficients of the quadratic equation of Y in X, i.e., Y = a X + a X
1 2
Note 1 to entry: a and a change slowly en
...

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