Fabrication and Optical Characteristics of Photonic Crystal Nanocavities with Er,O-Codoped GaAs

Abstract

Er,O-codoped GaAs is a promising candidate for application to light sources including lasers and single photon emitters in fiber-optic communication, due to sharp luminescence from Er³⁺ ions at 1.54 μm and temperature insensitivity of their luminescence wavelength. In this contribution, we review our recent research activities regarding the formation and optical characteristics of two types of photonic crystal (PhC) nanocavities, L3-type two-dimensional (2D) and bridge-type PhC nanocavities. The computational method to design the PhC nanocavities is established to couple the cavity modes to the Er luminescence at 1.538 μm by using the finite-difference time-domain method. By optimizing several parameters including the lattice constant and radii of the holes, the simulated cavity Quality(Q)-factor of 10⁵ is obtained from the L3-type PhC nanocavities. Such designed cavity Q-factor can be further improved to 1.2 × 10⁶ from the bridge-type PhC nanocavities. Based on these numerical simulations, several bridge-type PhC cavities with different lattice constant are fabricated, in order to couple the cavity mode to the Er luminescence, and optical characterization at room temperature is performed utilizing micro-photoluminescence (μ-PL) measurements. Enhancement of Er luminescence due to coupling to the cavity mode of the 2D-PC nanocavities is observed. The observed experimental cavity Q-factors of L3- and bridge-type PhC nanocavities are 5.0 × 10³ and 1.2 × 10⁴, respectively. Furthermore, incident pump power dependence of Er luminescence in the bridge-type PhC nanocavity with higher cavity Q-factor exhibits superlinearity with excitation power, suggesting Er luminescence amplification. This result would pave the way towards the realization of lasers and highly efficient single-photon emitters based on rare-earth-doped compound semiconductors.