Characteristics of Polarized Electroluminescence from m-plane InGaN-based Light Emitting Diodes

Abstract

Polarized electroluminescence (EL) from m-plane InGaN-based blue light emitting diodes (LEDs) has been investigated. These LEDs comprised a ZnO transparent electrode as an anode, polished mirror-like sidewalls, and a polished backside with the reflective mirror to remove the light scattering due to the surface roughness. The polarization ratio at room temperature was 0.80, which was relatively high compared to known values and was considered to be close to the true value. The reduction of the light scattering is essential for the accurate measurement of the polarized emission. The EL spectra from different three planes, i.e., m-, c-, and a-planes, have been measured. The peak energies of spectra polarized parallel to m-plane, emitted from a-and c-plane sidewalls, agree with the values of the two components emitted from top m-plane surface. The strongest component was E ? c while the second strongest was E k c. The E k m component was extremely low compared with E k c.

High-brightness polarized light-emitting diodes

“…11,13,21 POLARIZED EMISSION IN M-PLANE GAN LEDS: ELECTRIC DIPOLE DESCRIPTION Spontaneous radiative recombination from electrons in the conduction band (CB), with atomic s orbital character, and holes in the valence bands (VB), with atomic p x , p y and p z orbital characters (Figure 1a), is given by Fermi's golden rule and is proportional to the quantum mechanical dipole moments between these states. The correspondence principle states that these quantum mechanical dipole moments are well described by electric oscillating dipole moments from classic electromagnetism, 22 oriented parallel to the direction of the corresponding p orbital.…”

“…This effect was later minimized by covering the sidewalls, backside and part of the top surface of the devices with light absorbing material 11,13,21 (see the section on 'Materials and methods'). The observation of a clear mode dispersion demonstrates the preservation of polarization of the guided modes extracted by the embedded PhCs.…”

“…6,7 Today, the availability of high-quality free-standing substrates along non-polar and semipolar crystal planes of GaN allowed the demonstration of high-effciency optoelectronic devices. 8,9 High polarization ratios (defined in equation (1)) have been reported in m-plane GaN LEDs, [10][11][12][13] however, such LEDs present poor light-extraction efficiency due to total internal reflection at the flat GaN/air interface. The common light-extraction improving schemes applied to LEDs rely on randomizing the light reflected off the interfaces (roughened interfaces 14 or patterned substrates 15 ) which increases the light output of m-plane LEDs but also randomizes the original intrinsic polarization of the emitted light.…”

Mechanisms of the Asymmetric Light Output Enhancements in $a$ -Plane GaN Light-Emitting Diodes With Photonic Crystals

“…In addition to the performance improvement, non-polar epi-material has the advantage of generating polarized light. Because the biaxial stress in the QWs splits the valence bands into the several states, linearly polarized emission was observed in non-polar GaN LEDs [5]- [7]. Non-polar GaN light sources have the opportunity to be applied to the backlight of flat panel displays [8], which has the advantage of removing one polarization film.…”

Impact of nitridation on structural and optical properties of MOVPE‐grown m‐plane GaN layers on LiAlO2

“…These are the absence of spontaneous and piezoelectric polarization leading to higher recombination efficiency in quantum well based light emitting diodes (LEDs) [1] and lasers [2] as well as an eased Mg incorporation enabling higher possible p-type doping levels [3]. Furthermore, the anisotropic crystal structure allows the emission of polarized light and the realization of polarization-sensitive detectors [4,5]. In this letter, we report about the growth of nonpolar, m-plane GaN on (100) LiAlO 2 .…”