RATRO — RAy-TRacing SimulatOr of Light Propagation

RATRO (RAy-TRacing SimulatOr of Light Propagation) is designed for modeling the light extraction from LED chips. It involves ray-tracing simulation of the light propagation from the active region, absorption and extraction from the LED die through the n- and p-contact layers and the wafer, providing the integral extraction efficiency and the radiation patterns of the emitted light.

Distribution of the light emission from the active region is calculated in SpeCLED and stored in the file imported into RATRO™ along with the heterostructure geometry. Patterned and ordinary surfaces of contact layers, electrodes, and wafer are supported.

The computed light propagation gives the light extraction coefficients, fractions of light extraction through all chip surfaces, and energy loss in each chip region.

RATRO shares the same graphical user interface (GUI) with SpeCLED to specify the chip geometry, while all input parameters specific for light extraction simulation are specified in RATRO tab. The results of the computation can be viewed in SimuLEDView viewer supplied within RATRO. The visualization tool provides information on the integral light extraction parameters, 3D distributions of light intensity in the near-field, 2D distributions of light intensity for the near- and far-field regions, and radiation patterns. 

The RATRO package provides ray-tracing simulation of the light propagation from the active region, absorption and extraction from the LED die through the n- and p-contact layers and the wafer, providing the integral extraction efficiency and the radiation patterns of the emitted light. The code implements the physical models of optical processes, based on the following assumptions:

  • The emission from the active region is symmetrical so that the total light intensity and radiation pattern are identical for both sides (top and bottom) of the active region.
  • Angular emission distribution from the active region can be specified as (I) uniform, (II) Lambertian, or (III) custom (user-defined table).
  • The active region emits monochromatic radiation. The effect of the radiation wavelength is accounted implicitly via the refraction coefficients assigned for each material.
  • The light transmission and reflection in the metal electrodes can be calculated from known material parameters or specified as user-defined transmission and reflection coefficients.

2D distribution of light emission from active region

Light extraction from an LED die with a shaped wafer

The input of necessary data generated by SpeCLED, specification of optical parameters, running and monitoring of simulation, and visualization of the results is done via Graphical User Interface (GUI) and SimuLEDView visualization tool, respectively. RATRO is supplied with the user manual and description of physical model.  

Hot-line support can be provided for customers. The support includes free of charge supply of updated versions released during the license period and technical consulting on RATRO operation.

Radiation pattern in the top hemisphere

Publications

“Modeling of III-nitride Light-Emitting Diodes: Progress, Problems, and Perspectives” by Sergey Yu. Karpov, Proc. of SPIE, vol. 7939 (2011) 79391C / DOI 10.1117/12.872842

“Current crowding effect on light extraction efficiency of thin-film LEDs” by M. V. Bogdanov, K. A. Bulashevich, O. V. Khokhlev, I. Yu. Evstratov, M. S. Ramm, and S. Yu. Karpov, PSS Vol. 7, No 7–8, 2124–2126 (2010)

“Effect of ITO spreading layer on performance of blue light-emitting diodes”, M. V. Bogdanov, K. A. Bulashevich, O. V. Khokhlev, I. Yu. Evstratov, M. S. Ramm, and S. Yu. Karpov, PSS Vol. 7, No 7-8, 2127–2129 (2010)

“Comparison of Alternative Approaches to High-Power Thin-Film LED Chip Design” by K. A. Bulashevich, O. V. Khokhlev, M. V. Bogdanov, M. S. Ramm, I. Yu. Evstratov, and S. Yu. Karpov, Proceedings of the Second International Conference on White LEDs and Solid State Lighting, Taipei (2009)

“Current spreading, heat transfer, and light extraction in multipixel LED array” by M.V. Bogdanov, K.A. Bulashevich, I.Yu. Evstratov, S.Yu. Karpov, PSS Vol. 5, No. 6, 2070–2072 (2008)