Dielectric cap disordering of GaAs/AIGaAs multiple quantum well by using plasma enhanced chemical vapour deposited SiN capping layer

Abstract

The multiple quantum well (MQW) structure is a good candidate for the monolithic integration of lasers and waveguides to realize photonic integrated circuits (PIC). For such an application, certain types of technique are needed to define different bandgaps at the active and passive part of the PIC. Quantum well disordering techniques [1-9] have been used to locally disorder the MQW structure without any regrowth and/or selective growth step. Since the disordering of MQW results in a blue shift in bandgap and an increase in refractive index near the bandgap, these techniques can be used to fabricate lasers and waveguides monolithically with only onestep epitaxial growth. There have been several techniques to selectively disorder III-V compound semiconductor QW structures, such as impurity induced disordering [1, 2], ion implantation disordering [3,4], and dielectric cap disordering [5-9]. Among these techniques, since the dielectric cap disordering technique introduces a much lower optical loss compared to the impurity induced disordering and ion implantation techniques which give high optical losses due to high number of defects and high doping concentrations introduced during the disordering process, this technlque is thought to be better suited for fabricating high performance optical waveguide devices. Since a SiO2 Capping layer induces a relatively larger blue shift than a SiN capping layer in a GaAs/A1GaAs QW system, SiO2 is generally used to promote disordering while SiN is used as a mask to prevent bandgap shifts in the capped areas of the devices [5], even though SiN has been used to promote disordering in InGaAs/InGaAsP QW systems [6]. In this study, a dielectric cap disordering of GaAs/ A1GaAs MQW structure using a PECVD SiN capping layer is reported. The blue shift increased together with the thickness of the SiN capping layer as reported for a SiO2 capping layer [7], the amount of blue shift being even larger than a SiO 2 capped sample. We use a GaAs/A1GaAs MQW laser structure which is grown by a metal organic chemical vapour deposition (MOCVD) technique on a Si-doped n ÷ GaAs substrate. The vertical structure of the MQW