Monolithic integration of III-V nanowire with photonic crystal microcavity for vertical light emission

Abstract

A novel photonic structure formed by the monolithic integration of a vertical III-V nanowire on top of a L3 two-dimensional photonic crystal microcavity is proposed to enhance light emission from the nanowire. The impact on the nanowire spontaneous emission rate is evaluated by calculating the spontaneous emission factor β, and the material gain at threshold is used as a figure of merit of this vertical emitting nanolaser. An optimal design is identified for a GaAs nanowire geometry with r = 155 nm and L~1.1 μm, where minimum gain at threshold (gth~13×10³ cm⁻¹) and large spontaneous emission factor (β~0.3) are simultaneously achieved. Modification of the directivity of the L3 photonic crystal cavity via the band-folding principle is employed to further optimize the far-field radiation pattern and to increase the directivity of the device. These results lay the foundation for a new approach toward large-scale integration of vertical emitting nanolasers and may enable applications such as intra-chip optical interconnects.

Lasing from individual GaAs-AlGaAs core-shell nanowires up to room temperature

“…Vertical emission has been recently observed from InGaAsGaAs nanopillars grown on silicon 14 and silicon metal oxide semiconductor field-effect transistors 15 by exploiting low-loss helically propagating modes for which the reflectivity of the NW substrate is high, despite the low index contrast. Furthermore, AlGaAs-GaAs NW lasers could be directly integrated into silicon and III/V photonic crystal nanostructures to facilitate highly directed vertical emission 38 or transferred onto photonic waveguides for use as integrated sources 39 . However, using III/V NWs as an integrated source for applications such as silicon optical interconnects should take advantage of the ability to grow NWs site selectively and, furthermore, the lasers should emit unidirectionally into the underlying silicon photonic hardware.…”

Nanowire Lasers

“…Despite the large refractive index mismatch between the nanowire's core and the surrounding medium (typically air), which favors strong confinement of the electric field, the diameter range for strong confinement of single or multiple guided modes has a minimum value and is scaled by the refractive index and emission wavelength of the semiconductor. For instance, efficient waveguiding can be achieved for a 100-nm-diameter GaN nanowire emission and a minimum~165-nm-diameter GaAs nanowire emission at 870 nm [52].…”

“…However, computing these reflections is not as straightforward as in a conventional ridge laser, as the plane wave approximation is no longer valid. The modal reflectivities at the end facets of nanowires with circular or hexagonal cross sections have been calculated with finite-difference time-domain (FDTD); the reflectivity of the first TE mode was found to attain 80%, almost twice that of the fundamental HE 11 mode [52]. This leads to mode competition and complicates the control of lasing.…”

“…4-d). Larrue et al investigated whether this geometry is convenient in terms of optimal light-matter coupling [52]. The Purcell Factor, defining the enhancement of spontaneous emission of a narrow lineshape dipole in a cavity [3] is a relevant measure; however, it must be remembered that nanowires are not point emitters or narrowband.…”

“…The reduction of gain at the lasing threshold, or, equivalently, the pump level, is another criterion. This means that a suitable design for the nanowire and PhC cavity can allow a substantial reduction of the lasing threshold of the nanowire and also raise the spontaneous emission factor to~0.3, which is a typical number for nanolasers [52]. The group of Notomi at Nippon Telegraph and Telephone (NTT) in Japan managed recently to show the Purcell effect in a single InAsP nanowire on top of an Si photonic crystal, but no lasing was observed [12].…”