High efficiency blue‐violet optical modulators of ZnSe/ZnMgSSe asymmetric coupled quantum wells

Abstract

We report a high efficiency blue-violet optical modulator consisting of ZnSe/ZnMgSSe asymmetric-coupled quantum wells (ACQWs). The modulator devices were designed based on the finite element method in the framework of the effective-mass approximation and grown by molecular beam epitaxy (MBE) systematically. The new device with an electron-resonant type ACQW of [ZnSe (6 ML) /ZnMgSSe (2 ML) /ZnSe (12 ML)] has revealed a large Stark shift of ∆E ∼ 34 meV at room temperature in low electric field condition of 480 kV/cm. The maximum modulation depth is 51% with transmission configuration, and the devices show very stable operation. Differential absorption coefficients ∆α between reverse bias of 0 and 24 V are −26000 cm −1 at the ground state exciton resonance (E e1−hh1 ), and +11500 cm −1 in transparent region below the ground state, which is promising for practical waveguide optical modulators for the short wavelength.1 Introduction A quantum confined Stark effect (QCSE) of excitonic transition is attracted for optical functional devices such as high speed light modulators, switches or self electro-optic effect devices (SEEDs) [1,2]. In these optical devices, high electric-field induced excitonic Stark effect plays essential role, where large Stark shift without exciton dissociation must be realized. We have made systematic study on the development of new short wavelength optical modulator using II-VI widegap compounds based quantum wells because of its large exciton binding energy (> 20 meV) [3,4]. Furthermore, asymmetriccoupled quantum wells (ACQWs) of II-VI widegap compounds have a big advantage on the large Stark shift under low electric field [3]. In our previous study, electron-resonant type asymmetric-coupled quantum wells (ACQWs) of ZnSe/ZnMgSSe have revealed enhanced Stark shift without saturation under high electric field [4].In this paper we present a high efficiency blue-violet optical modulator consists of ZnSe/ZnMgSSe asymmetric-coupled quantum wells (ACQWs) with modulation efficiency exceeding 50% at room temperature. The new device designed with an electron-resonant type ACQW has revealed a large Stark shift of ∆E ∼ 34 meV at room temperature in low electric field condition of 480 kV/cm and very stable device operation. Differential absorption coefficients ∆α between reverse bias of 0 and 24 V is +11500 cm −1 in transparent region below the ground state exciton resonance.