Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer
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Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer H. S. Djie and B. S. Ooi Center for Optical Technology, Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, PA 18015, USA. C. K. F. Ho, T. Mei, K. Pita, and N. Q. Ngo School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 ABSTRACT We report the intermixing enhancement using the Ge-doped sol-gel derived silica encapsulant layer in InGaAs/InGaAsP quantum-well laser structure. A bandgap shift of ~64 nm has been observed from 16% Ge-doped silica capped sample at an annealing temperature of 630ºC while the intermixing at the similar temperature can be effectively suppressed with the ebeam evaporated SiO2 encapsulant layer. Using our theoretical model, nearly identical activation energy of 1.7±0.5 eV was obtained from the intermixed sample with Ge-doped silica. Similar intermixing enhancement holds for high Ge-content cap in the intermixed GaAs/AlGaAs quantum-wells related to Ga vacancy injection. We postulate that the dissimilarity in interdiffusion behavior between 0% and 16% Ge-doped silica capped sample is only attributed to the difference in the number of beneficial vacancies that involve in the intermixing process. INTRODUCTION Bandgap engineering of quantum heterostructure at postgrowth level via the impurity-free induced vacancy disordering (IFVD) has been viewed as a simple and effective way to alter the quantum-well (QW) properties selectively across the wafer for monolithic photonics integration.1 The approach utilizes the control of generated vacancies through suitable dielectric layers to either promote or suppress the interdiffusion between well and barrier during the high thermal treatment. Although it has been successfully implemented in GaAs-based QWs, there remains a challenge for InP-based QWs due to the poor thermal stability of the material. Hence, low temperature IFVD process with adequate spatial selectivity is favorable not only for the QW material with a low thermal stability but also for the strained quantum nanostructures such as quantum-dots, which the high temperature induced strain relaxation must be avoided. As opposed to widely used dielectric cap encapsulants, there has been a growing interest to employ the commercially available spin-on-glass to promote IFVD in GaAs-based QWs.2 It is widely known that the spin-on-glass using the sol-gel method allows the flexible synthesis of stoichiometric-dielectric materials, in which the matrix material can be doped with a wide range of elements and concentration homogeneously in a simple and inexpensive way. Here, we report the use of sol-gel method as the dielectric encapsulant layer to induce the IFVD effect in InGaAs/InP QWs and GaAs/AlGaAs QWs. The extent of IFVD will be examined by doping such film with Ge. The presence of dopant in the silica is expected to change the film properties and therefore influences the atomic outdiffusion that contributes to the intermixing.3 Photolu
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