LATERAL INJECTION LASERS

Abstract

Since its invention in the 60's, the semiconductor laser has relied on vertical injection of electrons and holes in order to pump the active region to inversion. While many aspects of semiconductor laser development have seen tremendous innovation and marked progress, this vertical injection scheme has remained unchanged. In contrast, the electronic transistor has evolved from the early dominance of vertical injection to today's largely lateral injection CMOS platform, which yielded new performance, functionality, and integrability and enabled the astonishingly successful integrated circuit revolution. The lateral current injection laser offers advantages which go far beyond optoelectronic integrability: it enables new functionalities, post-fabrication processing and engineering, and in some aspects of normal operation it can lead to greatly improved performances. To realize its full potential, this new class of semiconductor lasers deserves the same attention and the intensive iterations of efforts in theory, design, fabrication, and experimental probing as its vertical cousin has been received. We introduce a first-principles, combined theoretical-experimental approach to the exploration of the LCI laser. It reveals the role of lateral ambipolar drift-diffusion of carriers in either hindering or, potentially, in enhancing the provision of gain to the desired optical mode; of two-dimensional bandstructure engineering of the injection path and active region to achieve low differential resistance and efficient modal gain provision; of selective formation and lateral positioning of heterojunction in enabling high-efficiency device operation; and of adiabatic injection of electrons and holes across diffusively-graded heterojunctions in facilitating carrier capture into 2D quantum well states. Our results point to the tremendous promise of lasers based on lateral injection of current in enabling vertical cavity lasers with vastly increased performance and functional diversity; multi-terminal devices such as lasers with capacitive gain and wave-length tunability; high-speed directly-modulated lasers with reduced chirp; and functional devices with directly integrated high-speed longitudinal modulation.