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EP-4735868-A1 - METHOD AND SYSTEM FOR CHARACTERISING AN OPTOELECTRONIC DEVICE

EP4735868A1EP 4735868 A1EP4735868 A1EP 4735868A1EP-4735868-A1

Abstract

The invention relates to a method for characterising electroluminescent devices, which comprises: • illuminating the electroluminescent devices, the illumination being configured to generate charge carriers; • acquiring a series of luminescence images emitted by recombining the charge carriers in the electroluminescent devices; • determining, from the series of images and for a given electroluminescent device, a luminescence curve (20) as a function of time; • determining, from the luminescence curve (20) as a function of time, at least one parameter representative of an electroluminescence delay T, this electroluminescence delay T corresponding substantially to the start of an emission of radiation by electroluminescence of the given electroluminescent device.

Inventors

  • CHARBONNIER, Matthieu
  • DAANOUNE, Mehdi
  • FAIFER, VLADIMIR

Assignees

  • Aledia

Dates

Publication Date
20260506
Application Date
20240624

Claims (20)

  1. 1. Method for characterizing a set of electroluminescent devices arranged in a matrix on a substrate (2), said method comprising: • at least one illumination of the set of electroluminescent devices by a light source (1) configured to generate charge carriers in the electroluminescent devices, • at least one acquisition of a series of luminescence images by a sensor (3) configured to capture radiation emitted by recombination of the charge carriers generated in the electroluminescent devices, • a determination of at least one parameter representative of an electroluminescence delay, said electroluminescence delay corresponding substantially to the start of an emission of radiation by electroluminescence of the given electroluminescent device.
  2. 2. Method according to the preceding claim further comprising a determination, from the series of luminescence images and for a given electroluminescent device of the set of electroluminescent devices, of a plurality of values representative of luminescence as a function of time, the determination of the at least one parameter representative of an electroluminescence delay being carried out from said plurality of values representative of luminescence as a function of time.
  3. 3. Method according to claim 1 further comprising a determination, from the series of luminescence images and for a given electroluminescent device of the set of electroluminescent devices, of luminescence values as a function of time, the determination of the at least one parameter representative of an electroluminescence delay being carried out from said luminescence values as a function of time.
  4. 4. Method according to claim 1 further comprising a determination, from the series of luminescence images and for a given electroluminescent device of the set of electroluminescent devices, of a luminescence curve (20) as a function of time, the determination of the at least one parameter representative of an electroluminescence delay being carried out from said luminescence curve (20) as a function of time.
  5. 5. Method according to the preceding claim in which the determination of the at least one parameter representative of the electroluminescence delay comprises: • a derivation of the luminescence curve (20) so as to obtain a derived luminescence curve (21), the at least one parameter representative of the electroluminescence delay being an interval AT between a time origin and a characteristic time corresponding to a maximum of said derived luminescence curve (21).
  6. 6. Method according to the preceding claim further comprising, after determining the at least one parameter representative of the electroluminescence delay, a calculation of external quantum efficiency EQE according to: EQE = L EL * AT | where LEL is a contribution of electroluminescence to a total luminescence, and AT the interval representing the electroluminescence delay.
  7. 7. Method according to any one of claims 5 or 6 in which the derived luminescence curve (21) has at least a first peak and a second successive peak, the time origin being taken at the level of the first peak and the characteristic time being taken at the level of the second peak to determine the AT interval.
  8. 8. Method according to claim 7, in which the at least one illumination is in the form of a staircase signal comprising two steps or a pulsed signal.
  9. 9. Method according to any one of the preceding claims in which the determination of the at least one parameter representative of the electroluminescence delay comprises: • a dimensionality reduction of the luminescence curve (20), for example by a first algorithm, configured to generate a set of statistical parameters making it possible to conserve at least 90%, preferably at least 95%, and preferably at least 99% of the variance of the luminescence curve (20).
  10. 10. Method according to the preceding claim further comprising a calculation of external quantum efficiency EQE from the set of statistical parameters, by a second algorithm typically based on machine learning.
  11. 11. Method according to any one of the preceding claims, in which the at least one acquisition is configured so that said images of the series of images present: • a spatial resolution such that the electroluminescent devices are individually resolved on said luminescence images, • a temporal resolution less than the duration of a transient emission phase of electroluminescent devices.
  12. 12. Method according to the preceding claim, in which the at least one acquisition is configured so that the series of luminescence images comprises at least five luminescence images during the transient emission phase of the electroluminescent devices.
  13. 13. Method according to any one of the preceding claims, in which the at least one acquisition of the series of luminescence images is carried out with an acquisition time less than or equal to 500 ns for each image of the series of luminescence images.
  14. 14. Method according to any one of the preceding claims in which the luminescence images have a spatial resolution less than or equal to one micrometer.
  15. 15. A method according to any preceding claim, wherein the at least one illumination comprises a plurality of illumination pulses, and wherein the at least one acquisition of a series of images comprises the acquisition of a luminescence image associated with each pulse of the plurality of illumination pulses.
  16. 16. Method according to claim 15, in which each acquisition is carried out at an instant ti = tO + i*ôt where tO is the start of an illumination pulse of the plurality of illumination pulses, with 50 ns < ôt < 500 ns, for i varying from 1 to n.
  17. 17. Method according to one of the preceding claims in which the at least one, or where appropriate each acquisition is carried out after a series of two consecutive illumination pulses.
  18. 18. System for characterizing a set of electroluminescent devices arranged in a matrix on a substrate (2), said system comprising: • a light source (1) configured to generate charge carriers in the light-emitting devices, • a sensor (3) configured to capture radiation emitted by recombination of the charge carriers generated in the electroluminescent devices, • a controller (4) configured to control an illumination of the light source (1), and to acquire a series of luminescence images by the sensor (3), • a processing module configured for: - determining a luminescence curve (20) as a function of time from the series of luminescence images and for a given electroluminescent device of the set of electroluminescent devices, and for - determining from said luminescence curve (20) at least one parameter representative of an electroluminescence delay, said electroluminescence delay corresponding substantially to the start of an emission of radiation by electroluminescence of the given electroluminescent device.
  19. 19. System according to the preceding claim in which the sensor (3) has a pixel size smaller than a characteristic dimension of electroluminescent devices, said sensor (3) typically having a spatial resolution less than or equal to one micrometer.
  20. 20. System according to any one of claims 18 to 19 in which the sensor (3) has a time resolution less than or equal to 500 ns.

Description

“Method and system for characterizing an optoelectronic device” TECHNICAL AREA The present invention relates to the field of technologies for microelectronics and optoelectronics. It finds a particularly advantageous application in the contactless control of optoelectronic devices, for example GaN-based micro-light-emitting diodes. STATE OF THE ART Typically, to form a self-emissive display screen comprising pixels emitting their own light, a plurality of optoelectronic devices of the LED (light emitting diode) or microLED or OLED (organic LED) type are required. These optoelectronic devices are first at least partly formed collectively on substrates, typically in the form of wafers, then the devices are generally assembled individually, typically on a screen support, to manufacture the final system, typically the self-emissive display screen. Before assembly, it is important to be able to test optoelectronic devices, collectively and/or individually, in particular to rule out malfunctioning devices. This avoids costly repairs or replacements at a later stage, at the system level. However, it is counterproductive or even harmful to form electrical contacts on optoelectronic devices in order to test them before assembly. Electrical contact testing is complex to perform, particularly on microLEDs, and increases the duration and cost of the manufacturing process. The presence of electrical contacts can also be problematic for subsequent assembly. Removing the contacts can therefore be required, with the risk of damaging the optoelectronic devices. A non-destructive testing method, which can be easily implemented at different stages of the manufacturing process, is a substantial challenge for the industrial manufacturing of systems comprising a plurality of LED-type optoelectronic devices. One solution is to develop “contactless” characterization techniques. US9823198B2 discloses a solution consisting of illuminating an LED array and measuring a luminescence response of this LED array, via a photodiode. The characteristics of the luminescence response, in particular in the transient part of the luminescence response, are interpreted to determine a junction photovoltage and an internal quantum efficiency in particular. However, this solution does not allow individual characterization of microLEDs. Nor does this solution allow precise determination of the contributions of photoluminescence and electroluminescence to the luminescence response of the LED array. The present invention aims to at least partially overcome the drawbacks of the solutions mentioned above. In particular, an object of the present invention is to provide a method for characterizing a set of electroluminescent devices, having improved precision and resolution. Another object of the present invention is to provide a system for characterizing a set of electroluminescent devices, making it possible to implement the characterization method. Other objects, features and advantages of the present invention will become apparent upon examination of the following description and the accompanying drawings. It is understood that other advantages may be incorporated. In particular, certain features and advantages of the characterization method may apply mutatis mutandis to the characterization system, and vice versa. SUMMARY To achieve the above-mentioned objectives, one aspect relates to a method of characterizing a set of electroluminescent devices arranged in a matrix on a substrate, said method comprising: - at least one illumination of the set of electroluminescent devices by a light source configured to generate charge carriers in the electroluminescent devices, - at least one acquisition of a series of luminescence images by a sensor configured to capture radiation emitted by recombination of charge carriers generated in the electroluminescent devices, - a determination of at least one parameter representative of an electroluminescence delay, said electroluminescence delay corresponding substantially to the start of an emission of radiation by electroluminescence of the given electroluminescent device. Luminescence essentially integrates two contributions: a contribution due to photoluminescence and a contribution due to electroluminescence. The phenomenon of photoluminescence corresponds to a simple absorption-re-emission of photons, for example directly in a quantum well. The photons coming from the illumination are absorbed by the device, which then presents an excited state. During de-excitation, the device will re-emit photons, typically of lower energy. This absorption-re-emission of photons occurs almost instantaneously, without delay (the re-emission delay which corresponds to the radiative lifetime is typically less than a nanosecond). The phenomenon of electroluminescence corresponds to an emission of photons by recombination of charge carriers (electrons-holes). The operation of electroluminescent devices is based on this phenomenon of