Emission and absorption properties of patterned LED with 2D PhC

Abstract

Photonic crystals (PhC) create platform for a new generation of optical and optoelectronical devices. The PhC structures have been patterned in GaAs-based light emitting diodes in order to modify their optical properties. Patterned diodes with two-dimensional PhC were investigated by measurements of emission and detection properties. Measured dependencies revealed effect of PhC on emission and photocurrent spectrum. IntroductionPhotonic crystals (PhC) push the limits of conventional optoelectronical devices and create platform for a new generation of components of integrated optoelectronics. The PhC structures have been recently employed as a way how to improve the light extraction efficiency (LEE) in light emitting diodes (LED) and modify the far-field pattern diagram [1][2][3]. LEE enhancement can be achieved by minimizing the total internal reflection in the diode surface by surface roughness or photonic band gap effect [4][5][6]. In case of large period structures, the PhCs work as a diffraction grating placed directly on the light source. Short period structures can generate a photonic band gap where photons with frequencies within the gap are not allowed to propagate, resulting in an enhancement of light extraction in the vertical direction from a LED [6]. Also these short period structures are able to modify the far-field pattern diagram [3].In this work we focus on fabrication of two-dimensional (2D) PhC structures prepared in LED surface with aim to modify far-field pattern diagram and to improve LEE from the LED surface. Conventional GaAs/AlGaAs based LED with triple quantum well in active region emitting at central wavelength of 850 nm was used [7]. The LED surface was patterned with 2D PhC of square symmetry and the effect of PhC on optical properties was analysed. ExperimentalThe LED structures were grown by low pressure metal organic vapor phase epitaxy on (001) oriented n-GaAs substrate. The LED structure consists of 800 nm n-doped Al 0.295 Ga 0.705 As confinement layer, the undoped quantum well (QW) active region and 1300 nm p-doped upper confinement Al 0.295 Ga 0.705 As layer. The structure was covered by 40 nm GaAs cap layer (Fig. 1a). The QW active region contains three 9 nm thick GaAs quantum wells separated by 24 nm thick Al 0.295 Ga 0.705 As barriers.