Freestanding GaN-based integrated photonics chip with ultra-micro LED and straight waveguide for visible light communication

We propose a freestanding GaN-based integrated photonics chip with ultra-micro LED and straight waveguide for visible light communication on GaN-on-silicon platform realized by double-side process. The ultra-micro LED and waveguide is prepared by dry etching for GaN, electron beam evaporation for metal electrode, plasma enhanced chemical vapor deposition (PECVD) and wet etching for SiO2. The silicon substrate under chip is totally removed by deep inductive coupled plasma (ICP) etching to realize the freestanding membrane. The ultra-micro LED emits visible light signal in blue range. The visible light signal is coupled into straight waveguide connected to ultra-micro LED, and transmitted to tip of waveguide end. The communication performance of chip is significantly influenced by the active area of LED. Ultra-micro LED could well confine the visible light signal in waveguide, and achieve greater modulation bandwidth. The technical difficulty of chip with ultra-micro LED is to make p-electrode pad on active area with ultramicro size. We realize p-electrode pad with relatively large size on ultra-micro LED with SiO2 isolation layer. Light transmission performance of chip verse current is quantitatively analyzed by measuring intensity of visible light transmitted to waveguide tip. Most of the light emitted from ultra-micro LED is well confined in straight waveguide. The light intensity of waveguide tip is strongly modulated by the geometric parameters of straight waveguide. Freespace visible light communication (VLC) test with 120Mbps random binary sequence is carried out to achieve high speed data transmission. This study provides a potential approach for GaN-based integrated photonics chip as ultramicro light source and passive optical device in visible range.