Photoluminescence Imaging Measurement System

Model : u-PLM-EX

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Items Specifications
u-PLM-EX a. Laser source: 635 nm, 100 mW with bandpass filters.
b. Measurement sample size: 200 mm (standard 100 mm up to 200 mm maximum).
c. Computer controller for excitation wavelength change.
d. Measurement speed : 8 minitues for 4" samples (GaInP sample type, 1 mm step size, Lamda/Peak/FWHM measurement).
e. Integrated excitation light source.
f. Spot size: < 100 um.
g. Wavelength range: 300-1100 nm.
h. Can measure 4" circular and rectangle samples (maximum).
i. Detector: Si CCD array detector.
Optical Fiber Guiders a. Multi-mode Optical Fiber with AR Coating Aspheric for PL signal from 300-2200 nm (efficiency~75%).
PL chamber a. Archromatic focusing optics for excitation wavelength (>250 nm ) .
b. Long Working Distance Focusing optics for 532 nm.
c. Broadband and high reflectance optics PL signal (From300 nm to 2000 nm)
d. White light source illumination and sample alignment.
e. 5 Mega pixels camera for sample Image and monitoring system.
f. Automatic filer wheel for black excitation wavelength (with Longpass filters 350 nm).
Sample Size and Mapping System a. Sample size: 200 mm maximum (standard 100 mm to 200 mm maximum).
b. Can do the mapping measurement for 4" circular and rectangle sample4.
c. Linear slide, resolution ≦1 um.
d. Double Axis Stage Controller.
e. Z axis manual stage adjustable,±5 mm working distance, resolution: 10 um.
f. 7L/min vacuum pump.
g. High-efficient condenser.
h. Shield box.
i. Three adapters for 2-inch and 6-inch and 26.5 x 26.5 mm samples.
Photoluminescence Measurement Sytem a. Wavelength range:300-1100 nm
b. Sensitivity: >450,000 counts/uW
c. Detector type:2048 back-illuminated Si CCD detector,QE=78%
d. Noise Ratio: 450:1
e. Dark Noise (counts RMS): 17
f. Dynamic range: 3800
g. 16 bit A/D
h. PRNU: ±3%
i. Integration time:2us ~20 sec
  • Single point measurement for PL/EL
a. Can measure single PL spectrum.
b. Can measure single EL spectrum (the software is euqipped with controller for source meter, customers need to prepare the source meter)
  • Arbitrary Multi-point spectrum measurement for PL
a. Can do the arbitrary multipoint photoluminescence spectroscopy measurement automatically in the scanning range of 200 mm x 200 mm.
b. Can do the arbitrary multipoint electroluminescence spectroscopy measurement automatically in the scanning range of 200 mm x 200 mm. (can integrate with source meter, customers need to prepare the source meter).
  • Full-area PL/EL/LBIC Scanning Imaging Function
a. Can do the full-area PL or EL scanning imaging function. (the maximum area 200 mm x 200 mm).
b. Can do the 2D or 3D drawing based on the scanning result.
c. Can output the measurement result into TXT, CVS and JPC file.
  • LBIC Measurement Function
a. Use laser can do the LBIC function by integrating the source meter users offered.
b. Scanning range for LBIC:200mm x 200mm.
c. Can do the 2D or 3D drawing based on the scanning result.
d. Light intensity analysis, wavelength location analysis, FWHM mapping analysis.
e. Measurement report.
f. Recipe edition function.
g. 2D and 3D drawing function.
Computer a. Computer and LCD with windows system, english version.
TRPL/PL/EL/LBIC/Reflectance integrated system.
Fast mapping method and algorithm approach.
● 10 to 20 X fast than normal mapping.
Multi excitation wavelength capability.
● From 266 nm up to 1550 nm.
Industrial analysis tool.
● Line profile, defect mapping, DBR measurement.
Flexible design.
● Offer 4-inch, 6-inch and 8-inch total solution.

Characterization on DBR structure of VCSEL laser cavity by u-PLM-EX

The DBR structure is the most important process for VCSELs. The design and production of the DBR deeply affect the performance of the VCSEL. Enli Tech u-PLM-EX adopts non-destructive optical detection methods to accurately detect and analyze DBR epitaxial structures. With user-friendly analyzing software users can efficiently conduct researches on VCSEL.

Enli Tech u-PLM-EX

What is VCSEL laser?

Vertical-cavity surface-emitting lasers (VCSELs) made their debut over 10 years ago. Since then, they have become a staple component for a wide range of applications, especially in networks. In general, VCSEL is a type of semiconductor laser device that emits a highly efficient optical beam vertically from its top surface. It has an active medium and two high reflectance mirrors in semiconductor process. Compare with traditional laser diode, VCSEL has the following advantages:

● Surface-Normal output
● Circular output beam
● Low beam divergence
● Extremely small active volumes
● Low threshold currents
● Single frequency
● Thermally stable operation
● High-speed 
● 1-D and 2-D dimensional array
● On-wafer testing
● Ease of integration

For now, VCSEL applications include fiber optic communications, 3D sensing, precision sensing, computer mice, laser printers and augmented reality.

Structure diagram of VCSEL
▲Fig 1. Structure diagram of VSCEL

What is DBR structure and why it is important?

To archive a SLM cavity in VCSEL, the laser resonator consists of two distributed Bragg reflector (DBR) mirrors parallel to the wafer surface with an active region consisting of one or more quantum wells for the laser light generation. The planar DBR-mirrors consist of layers with alternating high and low refractive indices. Each layer has a thickness of a quarter of the laser wavelength in the material to make excellent constructive interference, yielding intensity reflectivity above 99 %. High reflectivity mirrors are required in VCSELs to balance the short axial length of the gain region.

structure of DBR

Fig. 2 structure of DBR

In general, the upper and lower mirrors of VCSELs are doped as p-type and n-type materials, forming a diode junction. In more complex structures, the p-type and n-type regions may be embedded between the mirrors, requiring a more complex semiconductor process to make electrical contact to the active region, but eliminating electrical power loss in the DBR structure. Therefore, it is very important that to check the optical properties of DBR in VCSEL devices.

How to probe DBR ?

To check the optical properties of DBR, Enlitech uses an Interferometer structure to analyze reflectance of DBR. In general, using a broadband source to illuminate sample and then measure the reflectance spectrum. Basic on resonator structure, the reflectance of each-layer of DBR will be seen as interference patterns which is shown on Fig. 3.

Principle of DBR maeasurement

Fig. 3 Principle of DBR measurement

According to measured results, researcher/engineers can check finger number, height of center-band, width of center-band and F-P dip to fit the original design. On the other hand, it could be integrated with mapper to further perform quality control in manufacturing process.

What’s our feature?

1. Fast mapping:
 Enli Tech had developed an algorithm to increase acquisition time for spectral mapping and DBR mapping can be done in a few minutes with high resolution step. In general, for 4-inch wafer with 1 mm resolution, it takes less than 5 minutes.
2. Broad wavelength range: 350 nm-2500 nm
 To measure reflectance mapping in DBR analysis, it must be equipped a highly stable and broadband light. Meanwhile, the collecting optics for spectral measurement also need be considered in an excellent mapper.The system equipped a long life (>10000 hrs) halogen lamp which spectral range is from 350 nm to 2500 nm. For detector part, it can installed visible or NIR array sensor for customer’s need.
3. Friendly analyzing Software: 
 To quickly analyzing the results of sample, software not only have basic tools for spectroscopy such as FWHM, Peak lambda, Peak intensity, but also have SB height, SB center, SB width and F-P dip analysis function. It could help researcher or engineer to quickly find out the defects and verify the processing parameters in their design.

1. Application Note AN-2137 FINISAR
2. Emanuel P. Haglund et al., “Hybrid vertical-cavity laser integration on silicon”, SPIE (2017)

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