WO2018121833A1

WO2018121833A1 - A method and apparatus for imaging an optoelectronic device or parts thereof

Info

Publication number: WO2018121833A1
Application number: PCT/EP2016/002198
Authority: WO
Inventors: Harald Hoppe; Roland Rösch; Rolf ÖTTKING
Original assignee: Friedrich-Schiller-Universität Jena
Priority date: 2016-12-31
Filing date: 2016-12-31
Publication date: 2018-07-05
Also published as: DE112016007564T5

Abstract

A method and apparatus for imaging an optoelectronic device (20) are described. The method comprises photonically stimulating (210) an area of a surface (25) of the optoelectronic device (20); and collecting infra-red radiation (220) from regions of the optoelectronic device (20). The collected infra-red radiation can be correlated with the photonic stimulation.

Description

Title: A method and apparatus for imaging an optoelectronic device or parts thereof. Field of the Invention

[0001] The application relates to a method and apparatus for stimulating and infra-red imaging an optoelectronic device or parts thereof.

Background of the Invention

[0002] Cameras for imaging optoelectronic devices, e.g. photovoltaic devices, are well known. These devices are used, for example, for monitoring the quality of the production of the optoelectronic devices. These cameras typically take a photograph of the optoelectronic device and analyse the image to identify defects in the optoelectronic device.

[0003] It is also possible to analyse in detail the operation of the optoelectronic device to identify whether the optoelectronic devices function correctly. This typically involves applying an electrical or optical stimulation signal to the optoelectronic device and seeing how the optoelectronic device reacts to the stimulation signal. One example of such a technique is the light-beam-induced-current LBIC method which is used to test the local functioning of photovoltaic cells.

[0004] It is, however, not practical to test all the optoelectronic devices as the testing is time- consuming. In practice a statistically relevant selection of the optoelectronic devices is chosen and individually tested. Should one of the optoelectronic devices be found to be defective, then others from the same batch or lot can be tested for correct functionality or sorted out directly.

[0005] Thermographic inspection of a semiconductor device is a technique that can be used to analyse a semiconductor device by imaging the thermal patterns of the semiconductor device. For example, Huth et al have described lock-in infrared thermography in a paper published in Solid-State Phenomena 82-84, January 2002. The thermographic inspection involves the introduction of periodically modulated heat into an object and monitoring the periodic surface temperature modulation with reference to the modulated heat supply. Summary of the Invention

[0006] This document describes a method for imaging an optoelectronic device or parts thereof. The method comprises photonically stimulating of the optoelectronic device, i.e. by using photons and subsequently collecting infra-red radiation from of the optoelectronic device. The collected infra-red radiation can be analysed and areas of the device with a different thermal profile identified. A computer system is used to correlate the collected infrared radiation with the photonically stimulated areas. These identified areas could indicate malfunctioning regions of any kind which can be investigated in detail. The malfunctioning regions could be a single device or plurality of devices or part of the device. Malfunctions include, but are not limited to, short circuits such as local shunts in the optoelectronic device. The method is non-destructive and enables rapid identification. The method requires a single excitation process, which allows more rapid analysis.

[0007] The optoelectronic device comprises a single element or a plurality of elements such as, but not limited to, photovoltaic devices or light-emitting diodes or integrated circuits including such elements.

[0008] The optical stimulation can be performed by means of a pulsed or on-off optical stimulation, e.g. by a flash, or passage through a light strip formed, for example, from a set of light sources or a mask with an opening. The on-off optical stimulation enables a large area to be investigated rapidly, whereas passing the optoelectronic device through a light strip enables a continuous and on-the-fly investigation during manufacture.

[0009] In one aspect, the infra-red radiation can be collected from a plurality of locations or after different time periods. This enables the time-dependency of the optical stimulation to be investigated, which may reveal further information about the optoelectronic device.

[0010] An apparatus for imaging of the optoelectronic device is also taught in this document. The apparatus comprises a radiation source for optically stimulating at least an area in the optoelectronic device and at least one radiation detector for collecting infra-red radiation from regions of the optoelectronic device. [0011] A processor runs a computer program for operating the apparatus and can time- correlate the optical stimulations from the stimulation device with the collected radiation from the radiation detector.

Description of the Drawings

[0012] Fig. 1 shows an outline of the apparatus of the invention in which an optoelectronic device is imaged.

[0013] Fig. 2 shows a flow diagram of the method of the invention. Detailed Description of the Invention

[0014] Fig. 1 shows an example of the apparatus 10 for the analysis of an optoelectronic device 20 in accordance with the teachings of this document. The optoelectronic device 20 has an upper surface 25 and the method is used to monitor temperatures of the regions of the optoelectronic device 20. The apparatus 10 comprises an optical stimulation source 30 and a radiation detector 40, such as a thermal imaging camera. The radiation detector 40 is connected to a computer system including a processor 50 which runs a computer program for the performance of the method outlined below and illustrated in Fig. 2. There could also be more than one radiation detector 40 mounted at several points in the apparatus 10.

[0015] The optical stimulation source 30 emits monochromatic or panchromatic radiation in a wavelength range of, for example, 200nm to 1 mm and at a power of between 1 and 10000 W/m². The optical stimulation source 30 could be a xenon lamp, a laser or a laser array or a set of LEDs. The optical stimulation source 30 could be a flash, a strip or array of separate light sources, or be formed by a mask with a slit through which the radiation shines onto the upper surface 25 of the optoelectronic device 20. The choice of the optical stimulation source, 30 depends on the type of optoelectronic device 20 being tested and the mode of testing. For example, a stationary optoelectronic device 20 being tested over its complete area will use a flashed optical stimulation source 30 for generating a single short pulse of light. On the other hand, a strip light is used as the optical stimulation source 30 for the testing of the

optoelectronic device 20 arranged as a continuous roll or as discrete optoelectronic devices 20 on a transport belt, e.g. emerging from a manufacturing device. The optoelectronic device 20 is passed briefly through the area of illumination, as indicated by the arrow in Fig. 1. For a continuous roll of optoelectronic devices 20 the arrangement enables the optoelectronic devices 20 to be tested in a continuous manner and over a long length.

[0016] The optoelectronic device 20 can be connected to an electrical source 35 which is connected through electrical connections 37 to the optoelectronic device 20 to provide a bias voltage to the optoelectronic device 20, if required. The voltage could further be applied to the optoelectronic device in a contactless manner, such as by principles of capacitative coupling or induction.

[0017] The radiation detector 40 detects infra-red radiation emitted from the surface of the optoelectronic device 20, for example, in the range of 700 nm to 20000 nm. Examples of such radiation detectors include, but are not limited to, InSb cameras that can image radiation in the wavelength between 2 and 5 μπι or a microbolometer focal plane array which can image radiation in the range of 7.5 to 14 μπι. It will be realised, however, that these values are not limiting of the invention. It will also be noted that an array of detectors arranged, for example, in a strip could be used.

[0018] The optoelectronic device 20 are semiconductor elements or coatings which can absorb light. The optoelectronic devices 20 could be, for example, a plurality of photonic devices, such as but not limited to photovoltaic devices, organic light emitting diodes or combinations of such devices with other components in an integrated circuit. The photonic devices are shown as elements 22 formed in the upper surface 25 of the optoelectronic device 20. The wavelength of the optical stimulation source 30 depends on the type of optoelectronic device 30 being tested. For example, the wavelength of the radiation generally needs to be greater than the band gap of the semiconductor material if an optoelectronic device 20 is made of a semiconductor material. It is possible to use radiation of other wavelengths which will cause heating of the optoelectronic device 20.

[0019] The apparatus 10 is in one aspect part of a manufacturing line in which the

optoelectronic devices 20 are self-supporting on a roll or are located on a transport belt moving along the manufacturing line and are tested after or during production. The

optoelectronic devices 20 are transported through the optical stimulation source 30 and the radiation detector 40, as indicated by the arrow 15. It will be noted that the testing could be carried out when electrodes have been connected to the optoelectronic devices 20 to form a short circuit over serially connected devices, as this may allow inspection for shunts or blockage within serial connections.

[0020] The optical stimulation source 30 and the radiation detector 40 are all connected to a computer system, including the processor 50, by electrical connections. The processor 50 is connected to a display device 60 and data entry device 70, such as a keyboard or a touchpad. The computer system can drive the optical stimulation source 30 and generate an optical pulse to stimulate the optoelectronic devices 20.

[0021] The computer system correlates the generated optical pulse from the radiation source 30 with signals received from the radiation detector 40. If there is more than one radiation detector 40, the infra-red radiation from the optoelectronic device 20 is imaged at several locations. In one aspect, the optoelectronic device 20 is transported through the different radiation detectors 40 as noted above and thus the effect of decay over time in the

optoelectronic devices 20 can be investigated by time-correlating the signals from the different radiation detectors 40. In another aspect one and the same radiation detector 40 may collect information of the optoelectronic device over time by using sub-areas, e.g. lines of pixels, in the same radiation detector 40.

[0022] In a further aspect, there may be a further radiation detector operating, for example, in the UV, visible or near infrad-red range, which can correlate the infra-red radiation with other signals detected by the further radiation detector.

[0023] Fig. 2 shows a flow diagram for the implementation of the method. In a first step 200, an optical pulse is applied to the optoelectronic device 20. The optical pulse is initiated by the processor 50 and is either a flash light or is generated by passing the optoelectronic device 20 briefly through a light strip from the optical stimulation source 30.

[0024] The optoelectronic device 20 is stimulated in step 210 by the optical signal from the radiation source 30.

[0025] The optoelectronic device 20 will emit infra-red radiation in step 215 after being stimulated by the optical radiation in step 210. It will be appreciated that the infra-red radiation is generally emitted from the upper surface, but may be generated in lower layers of the optoelectronic device 20 or between layers of the optoelectronic device 20. The infra-red radiation may be emitted from regions, which do not necessarily equate to the stimulated areas, as it is possible that electric current generated in the illuminated area will lead to malfunction in an adjacent region.

[0026] The infra-red radiation is collected by the radiation detector 40 in step 220 and passed to the processor 50 in step 230. The processor 50 correlates in step 240 the infra-red radiation with the optical radiation to see how the optoelectronic devices 20 perform under optical stimulation. The correlation enables performance of the optoelectronic devices 20 to be analysed non-destructively and malfunctioning regions in one of the photonic devices 22 to be identified.

[0027] Examples of malfunctioning include failure of operation of or hot and cold spots within some of the photonic devices 22 on stimulation. The use of several different ones of the radiation detectors 40 or of an infra-red-sensitive camera as radiation detector 40 means that changes in time of the activity of the photonic devices 22 can be investigated as the photonic devices 22 move through the apparatus 10.

[0028] Examples of malfunctioning include failure of parts or restricted regions or spots within the optoelectronic device 20 or within some photonic device 22 under investigation. The use of several different ones of the radiation detectors 40 or of an infra-red-sensitive camera as radiation detector 40 means that changes in time of the activity of those regions can be investigated as they move through the apparatus 10.

[0029] Examples of the application include: [a] in case of a multitude of optoelectronic and electronic devices being combined within one common substrate, broken serial electric interconnections which could be detected by increased heat emission upon excitation by a broad-band pulsed light source; [b] detection of local shunting defects within a photovoltaic module during production. Upon transient excitation of the active area of the photovoltaic device with light of energy higher than the band-gap of the semiconductor used in the photoactive layer, charge carriers are generated and will either recombine localized or through nearby located shunting defects. The localized recombination will yield an evenly distributed heat emission signal (IR-radiation) over the area of the optoelectronic device., whereas the shunts will locally exhibit higher emission signals (also IR-radiation) due to the higher currents running through the shunts. A shunting defect may simply be a local connection between the two opposite electrodes of the photovoltaic device, e.g. caused by a pin-hole within the photoactive layer; [c] in case of electrical wiring of the optoelectronic device 20 and thereby forming a short circuit through a multitude of serially connected photovoltaic devices - e.g. within a monolithic photovoltaic module - defects associated with the serial interconnection between two adjacent ones of the photovoltaic devices could be detected by the method described here. The defects here include e.g. local shunting or insufficient conductivity within the serial connection by either too high or too low heat emission signals.

Reference Numerals

10 Apparatus

20 Optoelectronic device

22 Photonic device

25 Upper surface

30 Radiation source

35 Electrical source

40 Radiation detector

50 Processor

60 Display device

70 Data entry device

Claims

Amended Claims

1. A method for imaging an optoelectronic device (20), the method comprising:

photonically stimulating (210) an area of a surface (25) of the optoelectronic device (20); and

collecting infra-red radiation (220) from regions of the optoelectronic device (20).

2. The method of claim 1, wherein the optoelectronic device (20) comprises a plurality of elements (22), the elements being one of photovoltaic devices or light-emitting diodes or integrated circuits including photovoltaic devices or light-emitting diodes.

3. The method of claim 1 or 2, wherein the optical stimulation is one of a pulsed optical stimulation or passage through a light strip.

4. The method of any of the above claims, wherein the stimulating is carried out by

illuminating using radiation in the wavelength of 200 ran to 1.5 micrometer.

5. The method of any of the above claims, wherein the collecting of radiation is carried out at wavelength within the range of 700 nm to 20000 nm.

6. The method of any of the above claims, further comprising collecting infra-red

radiation (220) from a plurality of regions or after different time periods.

7. The method of any of the above claims, further comprising an additional detector for light detection within the UV-vis-NIR wavelength range.

8. The method of claims 7 where the detector is a camera or a line detector.

9. The method of any one of claims 1-6, further comprising correlating the photonic

stimulation with the collected infra-red radiation.

10. An apparatus (10) for imaging of an optoelectronic device (20) comprising:

a radiation source (30) for optically stimulating at least one area of the optoelectronic device (20);

RECTIFIED SHEET (RULE 91) ISA/EP at least one radiation detector (40) for collecting infra-red radiation from at least one region of the optoelectronic device (20); and

a computer system (50) for correlating the optical stimulation from the stimulation device (30) with the collected radiation from the radiation detector (40).

11. The apparatus (10) of claim 10, wherein the optoelectronic device (20) is movable within sight of at least one radiation detector (40).

12. The apparatus (10) of claim 10 or 11, wherein the radiation source (30) produces a photonic pulse.

13. The apparatus of one of claims 10 to 12, wherein the stimulation device (30) produces radiation in a range of 200 nm to 1500 nm.

14. The apparatus of one of claims 10 to 13, wherein the radiation detector (40) detects radiation in the range of 700 nm to 20000 nm.

15. The apparatus of any one of claims 9 to 14, further comprising an additional detector for light detection within the UV-vis-NIR wavelength range.

16. A computer program product stored on a non-tangible medium and comprising logic means for causing a processor to carry out the method of one of claims 1 to 9.

RECTIFIED SHEET (RULE 91) ISA/EP