IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 43, NO. 11, NOVEMBER 2007 1041 Comparison of Usability of Oxide Apertures and Photonic Crystals Used to Create Radial Optical Confinements in 650-nm GaInP VCSELs Tomasz Czyszanowski, Robert P. Sarzala, Lukasz Piskorski, Maciej Dems, Michal Wasiak, Wlodzimierz Nakwaski, Senior Member, IEEE, and Krassimir Panajotov Abstract—Threshold characteristics of GaAs-based 650-nm gal- lium indium phosphide (GaInP) vertical-cavity surface-emitting diode lasers (VCSELs) with two different optical confinement structures are investigated with the aid of a self-consistent, fully- physical VCSEL model. Efficacy of the optical confinement in- troduced by the oxide aperture is compared with an alternative single-defect photonic-crystal design with holes etched throughout the whole VCSEL. Initially, photonic-crystal VCSEL reveals 10% lower threshold electrical power than that of the analogous oxide-confined VCSEL. Further optimization of the current injection allows for an additional 20% threshold reduction. The photonic-crystal confinement concept appears to be a very prospective solution for VCSEL configurations, for which oxida- tion is unfeasible, e.g., for possible nitride or phosphide VCSELs. Index Terms—GaInP light emitter, numerical simulation, optical confinement, photonic-crystal vertical-cavity surface-emit- ting laser (PhC VCSEL). I. INTRODUCTION I N MANY prospective applications of vertical-cavity surface- emitting diode lasers (VCSELs), their stable fundamental- mode, high-output power operation is required even at elevated temperatures. Then hitherto known VCSEL designs should be equipped with more enhanced mode selectivity mechanisms than currently used ones. This may be achieved in the pho- tonic-crystal-confined VCSELs (PhC VCSELs), because their photonic-crystal (PhC) configuration enables a modification of the radial wave-guiding effect with the aid of a properly designed single-point-defect (or seven-point-defect) PhC struc- ture. Single-mode output power of 3.1 mW with more than 30-dB Manuscript received February 15, 2007; revised May 9, 2007. This work was supported in part by Foreign Fellowships for Young PhDs awarded by the Foun- dation for Polish Science under Grant No 3-T11B-073-29 from the Polish Min- istry of Science and Higher Education (MNiSzW), in part by the IAP Program of the Belgian Government, and in part by Geconcerteerds Onderzoeksactie (GOA), Fonds Wetenschappelijk Onderzoek Vlaanderen (FWO), and Onder- zoeksraand (OZR) of the Vrije Universiteit Brussels. T. Czyszanowski is with Department of Applied Physics and Photonics, Vrije Universiteit Brussels, 1050 Brussels, Belgium, and also with the Laboratory of Computer Physics, Institute of Physics, Technical University of Lodz, ul. Wolczanska 219, 93-005 Lodz, Poland (e-mail: tomasz.czyszanowki@p.lodz. pl). R. P. Sarzala, L. Piskorski, M. Dems, M. Wasiak, and W. Nakwaski are with Laboratory of Computer Physics, Institute of Physics, Technical Univer- sity of Lodz, 93-005 Lodz, Poland (e-mail: rpsarzal@p.lodz.pl; lukasz.pisko- rski@gmail.com; maciej.dems@p.lodz.pl; mwasiak@p.lodz.pl; nakwaski@p. lodz.pl). K. Panajotov is with the Department of Applied Physics and Photonics, Vrije Universiteit Brussels, 1050 Brussels, Belgium, and also with Institute of Solid State Physics, 1784 Sofia, Bulgaria (e-mail: kpanajotov@tona.vub.ac.be). Digital Object Identifier 10.1109/JQE.2007.904492 side-mode suppression ratio has been demonstrated for GaAs PhC VCSELs [1]. The PhC impact on the radiation field is not associated with a photonic band gap, but is associated with a slightly lower effective refractive-index value of the PhC area surrounding the central-defect (CD) wave-guide rather than that of the CD one. Hence, in a near future, the art of etching with carefully designed lattice of air columns will be probably as important in VCSEL technology as the selective oxidation of AlAs-rich layers at present. It is expected that PhC VCSELs will enable their applications in areas currently not achievable by hitherto known oxide-confined (OC) VCSEL structures. Emerging new applications in office and home networks as well as in car, ships and aircraft communication systems take advantage of plastic (polymer) optical fibers (POFs) [2]. POFs of much larger core than silica fiber exhibit additionally greater mechanical flexibility, which can dramatically reduce the cost of their installation. For relatively short distances and moderate data rates, POFs are currently the lowest cost media to use for optical interconnects and the simplest to connectorize. The most prospective active regions of the light source designed for POFs (650 nm) seem to be the GaInP–AlGaInP quantum wells (QWs), which can extend the visible region of emission spectrum from deep red to green. Depending on the In mole fraction, these QWs may be under tensile or compressive strain; the unstrained con- figuration occurs for In mole fraction equal to 0.52. The optical and electrical confinements in GaAs-based VCSELs are usually realized by selective oxidation of AlAs layer. That concept has been utilized by Lott et al. [3]. Recently, PhC VCSEL config- uration has been introduced as an effective solution improving the modal characteristics of the VCSEL [4]. However, their de- sign has been limited mostly to qualitative studies of the im- pact of the hole depth on the cold-cavity modal behavior [4]–[6]. The applied numerical method used was based on the planewave expansion for the lateral direction combined with the weighted index approximation for the axial one. There has been no work considering the PhC impact with a fully vectiorial, 3-D method combined with electrical, thermal, gain, self-consistent models as we present here. Additionally, another group analyses the cold-cavity modal behavior of PhC VCSEL with holes incorpo- rated into the whole VCSEL [7] and compares the OC VCSEL with the PhC one [8], but thermal and electrical phenomena have been analyzed in a nonselfconsistent manner. Both papers are based on the scalar, optical effective index method. In the pre- sented paper, the efficacy of the PhC and OC optical confine- ment schemes are compared and their impact on the threshold characteristics of the 650-nm GaAs-based GaInP VCSELs is 0018-9197/$25.00 © 2007 IEEE