Effects of built-in polarization on InGaN-GaN vertical-cavity surface-emitting lasers

Abstract

Abstract-We investigate the effect of built-in spontaneous and piezoelectric polarization on the internal device physics of current-injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with strained InGaN quantum wells. Advanced device simulation is applied to a previously manufactured device design featuring dielectric mirrors and an indium-tin-oxide current injection layer. Contrary to common perception, we show: 1) that only a small fraction of the built-in quantum-well polarization is screened at typical injection current densities and 2) that the polarization of the AlGaN electron stopper layer has a strong effect on the VCSEL threshold current which can be partly compensated for by higher p-doping.Index Terms-Electron leakage, GaN-based light emitter, InGaN quantum well, numerical simulation, piezoelectric effect, polarization, vertical-cavity surface-emitting laser (VCSEL). P IEZOELECTRIC and spontaneous polarization is known to be much stronger in c-plane GaN-based alloys than in other III-V compounds. Extensive experimental and theoretical work has been invested in this phenomenon, and nonlinear analytical approximations have been derived for calculating the built-in polarization [1]. Polarization strongly affects radiative recombination processes in strained InGaN quantum wells which are typically employed in GaN-based light-emitting devices [2]. The polarization-induced electrostatic field leads to a separation of electrons and holes within the quantum well and thereby to a reduction of the photon emission rate. However, for GaN-based lasers, polarization effects are usually considered less important because the high density of electrons and holes in the quantum wells is assumed to screen the built-in polarization charges [3].Using advanced device simulation, we investigate the effects of polarization on the internal physics and the threshold current of InGaN-GaN laser diodes. Our software self-consistently combines wurtzite quantum well band structure calculations, radiative and nonradiative carrier recombination, carrier drift and diffusion, and optical mode computation [4]. More details of the model are described elsewhere [5]. Previously, we used a very similar model to study edge-emitting high-power InGaN-GaN lasers, demonstrating good agreement with measurements [6].Here, we focus on InGaN-GaN vertical-cavity surface-emitting lasers (VCSELs), which are expected to exhibit several Manuscript

Electronic Properties of InGaN/GaN Vertical‐Cavity Lasers

“…At hetero-interfaces, the difference of these surface charge densities gives the net polarization charge density which is listed in Table 19.4 for the interfaces in our device. Built-in polarization fields are expected to strongly affect the VCSEL performance [32]. Within the quantum wells, the polarization field separates electrons and holes, thereby reducing stimulated and spontaneous emission.…”

Macroscopic Polarization Effect on Bowing Constant of Thermal Parameters of In x Ga1−x N

“…Recently, the effect of the polarization mechanism on the efficiency of LEDs and laser diodes was reported. [24][25][26][27] The reported results show that the efficiency drop is caused by several internal physical mechanisms including the built-in electrostatic field induced by the spontaneous and piezoelectric polarization. The effect of polarization has also been studied in the context of solar cell performance.…”

Progress and challenges in electrically pumped GaN-based VCSELs

“…However, an EBL will also affect hole injection into the QWs, and the EBL design is thus crucial for low-threshold operation. Many different EBLs have been proposed and their effect on VCSEL performance has been investigated such as different p-doping levels of the EBL 98 , compositionally graded EBL 99 , and multiple barrier EBL 100 .…”