A Comparative Study of an Inp Quantum Dot Laser and a GA x IN( 1-X )P Quantum Well Laser
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A COMPARATIVE STUDY OF AN INP QUANTUM DOT LASER AND A GAXIN(1-X)P QUANTUM WELL LASER Y. M. Manz and O. G. Schmidt Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stutttgart, Germany ABSTRACT A comparative study between a red-light emitting quantum dot (QD) and quantum well (QW) laser, grown in the same solid-source molcular beam epitaxy (SSMBE) machine under the same conditions, is presented. The QD laser consists of a threefold stack of 3.5 ML InP dots and the QW laser of a 4.5 nm thick compressively strained Ga30In70P layer, both embedded in a Ga52In48P waveguide. The threshold current density of the QD laser is jthr = 1.8 kA/cm2 at 300 K and more than twice as large for the QW laser. Moreover, temperature dependent analysis of spontaneous emission spectra reveals that the threshold current density of the QD device is less temperature dependent than that of the QW laser, although the linewidth of the QD samples is larger. INTRODUCTION Quantum dot lasers promise to have superior characteristics to quantum well lasers due to their atomlike density of states [1], [2]. Much effort has been put into improving the QD laser performance such as the threshold current density. Values as low as 24 A/cm2 have been reported for InAs QD lasers at room temperature, emitting at 1.28 µm wavelength [3]. Redlight emitting QD lasers have been realized with AlInAs/AlGaAs QDs [4, 5] and InP/GaInP QDs [6-8]. Recently, we reported the first room-temperature InP/GaInP QD injection laser [9]. Also QW lasers, based on strained GaxIn(1-x)P wells, embedded in quaternary (AlyGa(1-y))52In48P emit in this wavelength regime and show threshold current densities of 370 A/cm2 with antireflecting/highreflecting coated cavity mirrors [10]. A comparison between a QW and a QD laser, grown under exactly the same conditions has not been reported, yet. In this contribution lasing characteristics of InP quantum dots are compared with a compressively strained Ga30In70P quantum well, embedded in a ternary Ga52In48P waveguide, GaAs lattice matched - both devices grown in the same solid source molecular beam epitaxy machine under identical growth conditions. EXPERIMENTAL METHODS The two laser samples discussed here are shown in figure 1. They were grown by SSMBE on n+-GaAs (001) substrate. The structures differ only in the optically active region, which consists of a threefold stack of 3.5 ML InP QDs with 4 nm Ga52In48P spacer layers for the QD device and of a single 4.5 nm thick Ga30In70P layer for the QW device, both embedded in a 120 nm thick Ga52In48P waveguide.
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The p- and n-type cladding layers consist of 900 nm Al53In47P, doped with Si and Be with a maximum doping concentration of about 2 × 1018 cm-3 and 5 × 1017 cm-3, respectively. The structures are capped by a p+-GaAs layer. The ma
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