| Molecular-beam epitaxy (MBE) has evolved over the past 20 years as one of the most important tools in the study of solid-state physics and the development of semiconductor technology, especially that which involves the compound semiconductors. It is an ideal technique for epitaxial growth of semiconductor devices due to its precise control over layer thickness, alloy composition and interface abruptness. This precise control is especially important for the epitaxial growth of vertical-cavity surface-emitting laser (VCSEL) diodes, for their efficient operation requires high quality epitaxial material and a match between the reflectivity spectrum of the semiconductor quarter-wave stack distributed Bragg reflector (DBR) and the emission spectrum of the quantum well (QW) active region. These devices are of considerable technological importance due to advantages which are inherent to their geometry, including a wide mode spacing, potential for ultra-low threshold currents, a narrow, symmetric beam divergence, and compatibility with optoelectronic integration.;We discuss experimental techniques and results relating to studies which advance the optoelectronics technology, and our understanding of fundamental physics. MBE is used to grow epitaxial structures in which a QW is precisely placed either in close proximity to a DBR, or near the surface of the epitaxial layer, so that a highly reflective mirror can be placed in close proximity to the QW. These structures are incorporated into studies of the rather unique effects resulting from the electrodynamics which occur when localized dipoles emit spontaneously within a coherence length of a reflector.;DBRs are epitaxially grown above and below a QW in order to form an optical cavity with the QW optical emission source within. This structure is fabricated into VCSEL diodes. The particular challenges that such experiments present to the MBE crystal growth technology are discussed, and unique abilities of MBE such as epitaxial growth of thin, highly resistive layers are applied to the advancement of VCSEL technology. With such structures we are able to fabricate state-of-the-art VCSELs with high efficiency and the lowest bias voltages for room-temperature, continuous-wave lasing operation reported to date for devices of this size. |
