Spatial Bandgap Tuning in Long Wavelength InAs Quantum Dots-in-Well Laser Structure
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Spatial Bandgap Tuning in Long Wavelength InAs Quantum Dots-in-Well Laser Structure Yang Wang, Clara E. Dimas, Hery S. Djie and Boon S. Ooi Center for Optical Technologies and Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 Gerard Dang and Wayne Chang U. S. Army Research Laboratory, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, Maryland 20783 ABSTRACT We employed the postgrowth impurity-free vacancy diffusion technique to selectively tune the bandgap of the InAs/InGaAlAs dots-in-well laser structure grown on (100) InP substrate. A blueshift up to 170 nm with a significant decrease in the photoluminescence linewidth has been observed. Spatial control of the bandgap shifts has been achieved using SiO2 and SixNy layers as annealing caps. A differential wavelength shift of 76 nm has been observed after a rapid thermal annealing step at 750°C for 30 s. In contrast to most reported results in other material systems using similar process, we observed a larger bandgap shift from the SixNy capped samples than from the SiO2 capped samples. Our theoretical calculation indicates that the unusual intermixing behavior in this material system is governed by different interdiffusion rates of group-III atoms. INTRODUCTION The InAs QD grown on InP substrate has been seen as a promising approach to obtain long wavelength emission of ~1.55 µm for optical fiber telecommunication applications [1-3]. However, the QD usually produces emission wavelength above 1.6 µm at room temperature (RT) and the precise control of the emission at a shorter wavelength during the epitaxial growth remains a challenge [3]. This is primarily due to the small lattice mismatch (~3.2%) between InAs and the InP matrix layer, resulting in relatively large QDs and shifting the emission wavelength beyond 1.6 µm. In addition, the presence of As/P exchange during the InAs QD growth and anisotropic stress relaxation further complicates the reproducible formation of high quality QDs on InP substrate with a controllable wavelength. Thermal induced QD intermixing (or interdiffusion) is a subject of extensive research driven by the prospect of fabricating photonic integrated circuits, as well as by the need for fine trimming material properties at a postgrowth level. Several approaches, including impurity-free vacancy diffusion (IFVD) [4], impurity-induced disordering [5], and laser induced intermixing [6] has been used to achieve QD intermixing. Most of these studies focus on the group-III intermixing of In(Ga)As/GaAs QDs in the short wavelength region (0.9-1.3 µm). At long wavelengths (1.3-1.6 µm), group-V intermixing in InAs QDs embedded in the InP matrix has been reported [6]. In this paper, we report spatial bandgap tuning of InAs/InGaAlAs quantum dots-in-well (DWELL) laser structure based on IFVD technique via group-III intermixing. The IFVD effect is discussed in association with the multiple cations interdiffusion model to explain the selective intermixing behavior under different dielectric ca
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