Development of a III-nitride electro-optical modulator for UV–vis

Abstract

We present first experimental results of a novel electro-optical modulator for UV–vis based on III-nitrides. This device consists of a modulation layer which changes its complex dielectric constant influenced by the electric field and a field-dependent carrier distribution. Here, we fabricated and investigated different configurations for the modulation layer structure. The core of the structures was a p–i–n structure in which the i-layer was either GaN or AlGaN. Furthermore, a conventional undoped AlGaN/GaN heterostructure containing a two-dimensional electron gas was grown. Samples were characterized by high-resulution X-ray diffraction (2theta-omega scans and reciprocal space mappings), atomic force microscopy and capacitance–voltage measurements; the reflectivity modulation was determined using a UV–vis white-light reflectometer and a DC voltage source. The results show that reflectivity modulation is readily achieved, caused by the control of the charge carrier density and the electric field. We obtained a relative change in reflectivity of ±1.5% from −8 V to +2 V.

Design and analysis of high electron mobility transistor inspired: III-V electro-optic modulator topologies

“…The AlGaN/GaN HEMT free space modulator has limited interaction length of light with 2DEG, which will result in modulation depth < 10%, as has been reported for THz wave modulators based on 2DEG [38] and recently for UVvis 2DEG modulators [23]. This can be improved in a waveguided implementation of this structure, where the heterostructure interface can be designed to overlap with the core of the waveguide that has the largest optical mode intensity.…”

“…A large driver of the performance superiority in GaN HEMTs is the electrically tunable, highly localized sheet of charge (two dimensional electron gas: 2DEG) formed at the III-V heterostructure interface due to spontaneous and piezoelectric polarization in the constituent materials [13]. Recently, a 2DEG based modulator in AlGaN/GaN platform was demonstrated operating in the UV-vis wavelength ranges [23], however the modulation mechanism due to plasma dispersion effect of 2DEG was not systematically studied. In this paper, we propose and analyze electro-optic modulator design topologies inspired by III-V HEMTs in a GaN technology platform.…”

Design and analysis of electro-optic modulators based on high contrast gratings in AlGaN/GaN heterostructures

“…GaN based devices not only find applications in high power devices but also in electro-optic devices owing to Pockels effect and the large band gap in GaN 3.4 eV [16,17] and several devices leveraging the quantum-confined stark effect in multi-quantum well structures [18,19] and Franz-Keldysh effect [20,21] in III-nitrides have been explored. Recently we reported various design topologies for EOMs leveraging the plasma dispersion effect of 2DEG in AlGaN/GaN heterostructures [22] and 2DEG based EOMs operating in the UV-Vis wavelength range were reported by Wieben et al [23] The 2DEG is confined in an atomistically thin layer at the heterostructure interface, which results in limited optical interaction length and thereby small phase shift ≈ 1 × 10 −5 rad [22]. This necessitates incorporating the HEMT into a resonant cavity to boost the modulation index.…”