Designs And Simulations Of GaN-based LED With Monte Carlo Photon-tracing Method

With advantages such as energy saving, long lifetime, and small size, light-emitting diodes (LEDs) is considered as a revolutionary light source of next generation and attract wide attention. Due to the refractive index difference between chip and air, the light extraction efficiency (LEE) becomes an important factor of LED performance improvement and a research hotspot in recent years. In this article, the Monte Carlo photon-tracing method and the program flow are introduced detailedly. By computer simulation of face-up GaN-based light-emitting diodes (LEDs) and vertical LED with Monte Carlo photon-tracing method, and the mechanism of light extraction is discussed.Although face-up LEDs do not have an excellent performance, but they still have a wide use because of simple manufacture and low cost. In this article, light extraction simulation of face-up GaN-based light-emitting diodes (LEDs) is presented, and the influence factors of LEE are studied. It is shown that the light extraction efficiency can be improved significantly by increasing refractive index of encapsulation material mainly when the refractive index of encapsulation material is smaller than the refractive index of transparent conductive thin film; when the sapphire thickness increases, the light extraction efficiency will increase rapidly first and then be saturated, so the light extraction improvement and heat dissipation of sapphire thickness should both considered during manufacturing process of LED; besides, transparent conductive thin film with low absorption coefficient and high reflectivity bottom reflector can also improve the light extraction efficiency significantly.Vertical GaN-based LEDs have advantages in current injection, heat dissipation, reliability and so on. A venation-like groove structure (VGS) is proposed to improve light extraction efficiency (LEE) of vertical GaN-based light-emitting diode by reshaping the undoped GaN (U-GaN) layer. The light extraction characteristics of the venation-like groove structure are simulated and compared to other structures by the Monte Carlo photon-tracing method. It is found that VGS has advantages against other structures. At the chip size of 300μm×300μm, the LEE of VGS is 20.5 %, 12.1 % and 7.2 % higher than that of VNGS, IGS and SGS, respectively. These advantages are mainly contributed to the partition and deformation in VGS. Further, we study the mechanism through drawing LEE distribution patterns, comparing the LEE of different areas and simulating chips with different groove-depth.