Vertical cavity surface emitting laser with self-assembled quantum dots

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 techniques3-5) 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.