Method and apparatus for non-contact measurement of internal quantum efficiency in light emitting diode structures

Patent metadata

Field	Value
Publication number	US-9823198-B2
Application number	US-201414485468-A
Country	US
Kind code	B2
Filing date	Sep 12, 2014
Priority date	Sep 14, 2013
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

Non-contact measurement of one or more electrical response characteristics of a LED structure includes illuminating an illumination area of a surface of a light emitting diode structure with one or more light pulses, measuring a transient of a luminescence signal from a luminescence area within the illumination area of the light emitting diode structure with a luminescence sensor, determining a first luminescence intensity at a first time of the measured transient of the luminescence signal from the light emitting diode structure, determining a second luminescence intensity at a second time different from the first time of the measured transient of the luminescence signal from the light emitting diode structure and determining an intensity of the electroluminescence component of the luminescence signal from the light emitting diode structure based on the first luminescence signal and the second luminescence signal.

First claim

What is claimed:

1. An apparatus for contactless measurement of one or more characteristics of a light emitting diode structure comprising:
an illumination unit including an illumination source for illuminating an illumination area of a substrate including a light emitting diode structure with light of a selected intensity amplitude, the light including at least one of intensity modulated light or pulsed light, the light suitable for stimulating photoluminescence within at least a first area of the light emitting diode structure of the illumination area;
a luminescence measurement unit including at least one optical sensor configured to measure a luminescence signal from the first area of the LED structure within the illumination area;
a junction photovoltage measurement unit including at least a first transparent electrode positioned proximate to the light emitting diode structure and configured to transmit light from the illumination source to the first area of the LED structure, wherein the first transparent electrode is configured to measure a junction photovoltage signal of the light emitting diode structure corresponding with the first area within the illuminated area, wherein the area of the first electrode is smaller than the illumination area illuminated by the illumination unit; and
a controller communicatively coupled to at least the luminescence measurement unit, the junction photovoltage measurement unit and the illumination unit, the controller configured to:
control one or more characteristics of the light from the illumination source;
receive one or more measurements of the luminescence signal from the luminescence measurement unit;
receive one or more measurements of the junction photovoltage signal from the junction photovoltage measurement unit; and
determine at least one of an internal quantum efficiency or an internal injection efficiency of the light emitting diode structure based on one or more characteristics of the received one or more measurements of the luminescence signal and one or more characteristics of the received one or more measurements of the junction photovoltage signal.

2. The apparatus of claim 1 , wherein the controller is further configured to:
determine at least one of an internal quantum efficiency or an internal injection efficiency of the light emitting diode structure with at least one of a determined junction photovoltage forward voltage of the light emitting diode structure from the luminescence area, a photocurrent density of the light emitting diode structure or an intensity of the electroluminescence component of the luminescence signal.

3. The apparatus of claim 1 , wherein the illumination source comprises:
an illumination source configured to emit light modulated at a selected modulation frequency.

4. The apparatus of claim 1 , wherein the illumination source comprises:
an illumination source configured to emit pulsed light of a selected magnitude and pulse duration.

5. The apparatus of claim 1 , wherein the illumination source comprises:
at least one of a light emitting diode, a laser or a filtered flash lamp.

6. The apparatus of claim 1 , wherein the junction photovoltage measurement unit further includes:
one or more signal processing elements.

7. The apparatus of claim 6 , wherein the one or more signal processing elements comprise:
at least one of a preamplifier or detector.

8. The apparatus of claim 1 , wherein the luminescence measurement unit further includes:
one or more signal processing elements.

9. The apparatus of claim 8 , wherein the one or more signal processing elements comprise:
at least one of a preamplifier or detector.

10. The apparatus of claim 1 , wherein the substrate including a light emitting diode structure is disposed on a chuck.

11. The apparatus of claim 10 , further comprising:
a signal generator electrically coupled to the chuck via a switch.

12. The apparatus of claim 1 , wherein the one or more characteristics of the luminescence signal comprise:
at least one of a transient of the luminescence signal or an amplitude of the luminescence signal.

13. The apparatus of claim 1 , wherein the one or more characteristics of the junction photovoltage signal comprise:
at least one of a transient of the junction photovoltage signal or an amplitude of the junction photovoltage signal.

14. The apparatus of claim 1 , further comprising:
a transparent element configured to secure at least the first transparent electrode.

15. The apparatus of claim 1 , further comprising:
at least one conducting pad electrically coupling a p-layer of the light emitting diode structure to an n-layer of the light emitting diode structure.

16. The apparatus of claim 1 , further comprising:
an additional electrode disposed on a vertical stage and positioned proximate to the light emitting diode structure.

17. A method for contactless measurement of one or more characteristics of a light emitting diode structure comprising:
illuminating an illumination area of a surface of a light emitting diode structure with one or more light pulses;
measuring a transient of a luminescence signal from a luminescence area within the illumination area with a luminescence sensor;
measuring a transient of a junction photovoltage signal from the luminescence area within the illumination area with a transparent electrode positioned within the illumination area and proximate to the surface of the light emitting diode structure;
determining a junction photovoltage forward voltage of the light emitting diode structure from the luminescence area;
determining a photocurrent density of the light emitting diode structure;
determining an intensity of an electroluminescence component of the luminescence signal; and
determining at least one of an internal quantum efficiency or an internal injection efficiency of the light emitting diode structure with at least one of the determined junction photovoltage forward voltage of the light emitting diode structure from the luminescence area, the photocurrent density of the light emitting diode structure or the intensity of the electroluminescence component of the luminescence signal.

18. The method of claim 17 , wherein the junction photovoltage forward voltage of the luminescence area is determined based on the amplitude of the junction photovoltage signal measured from the luminescence area with the transparent electrode.

19. The method of claim 17 , wherein the determining a photocurrent density of the LED structure comprises:
determining a derivative of the transient of the JPV signal at a front edge of the JPV signal;
acquiring a capacitance of a p-n junction of the LED structure; and
calculating the photocurrent density of the LED structure with the derivative of the transient of the JPV signal at a front edge of the JPV signal and the capacitance of the p-n junction of the LED structure.

20. The method of claim 17 , wherein the determining an intensity of an electroluminescence component of the luminescence signal comprises:
applying pulsed illumination to the light emitting diode structure having a first time interval corresponding with the junction photovoltage forward voltage being lower than a turn on voltage of the electroluminescence signal based on the transient of the junction photovoltage;
applying pulsed illumination to the light emitting diode structure having a second time interval corresponding with the junction photovoltage forward voltage being higher than the turn on voltage of

Assignees

• Kla Tencor Corp

Inventors

• Faifer Vladimir N

Classifications

• G01N2033/0095

  Physics · mapped topic

• G01R31/2635

  Testing light-emitting diodes, laser diodes or photodiodes · CPC title

• G01N33/00

  Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00 · CPC title

• G01N21/66 Primary

  electrically excited, e.g. electroluminescence · CPC title

• G01N33/0095

  Semiconductive materials · CPC title