Abstract

Recently, low-dimensional quantum structures such as quantum dots (QDs) and quantum wires (QWIs), has been attracting much interest due to their novel physical properties and consequent improvements in device performances.¹⁾ When the ideal QD or QWI structures are achieved, higher gain and lower threshold current in laser diodes are expected.²⁾ Among the many fabrication methods reported for such structures, self-assembled quantum-dot (SAQD) growth techniques^3-5) are particularly notable. They positively utilize the islanding growth in highly strained heteroepitaxial systems, such as InGaAs on GaAs. The SAQDs can be simply fabricated by molecular beam epitaxy (MBE)³⁾ or metal-organic vapor phase epitaxy (MOVPE)^4),5) and they have high crystal quality and uniform size distributions of within 10% as well as high surface densities of more than about 10¹¹cm^-2. Using these SAQDs, low-threshold QD edge-emitting lasers have been fabricated.^6-8) We expect to make even more advanced lasers, such as QD vertical-cavity surface-emitting lasers (VCSELs) using QDs in the active region.⁹⁾ The QD-VCSEL is especially attractive for controlling both the electron and photon modes in a microcavity structure.¹⁰⁾ When the cavity mode coincides with the narrow bandwidth light emission that originates from the delta-function-like density of states in uniform QDs, a high-performance light source with very low threshold current can be realized. On the other hand, the gain width, which critically determines the temperature characteristics of the VCSEL,¹¹⁾ can be designated in QD-VCSELs by controlling the dot size distribution. Therefore, for improving and modifying device performances, we believe that the QD-VCSEL is the optimum optical device utilizing the QD structure. In this article, we report the fabrication of a QD-VCSEL and the observation of lasing oscillation at room temperature.

© 1997 Optical Society of America