ISSN 1063-7826, Semiconductors, 2008, Vol. 42, No. 7, pp. 852–857. © Pleiades Publishing, Ltd., 2008. Original Russian Text © T.E. Slobodyan, K.A. Bulashevich, S.Yu. Karpov, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 7, pp. 871–877. 852 1. INTRODUCTION In the first part of this study (see [1]), we derived wave equations for the waveguide modes that have TE and TM polarization and propagate in optically uniaxial laser heterostructures formed on the basis of nitrides of Group III elements; we also formulated the necessary boundary conditions for components of the electromag- netic field [1]. As a result of the analysis of experimen- tal data on optical properties of both nitrides of Group III elements and the substrate materials (sapphire, GaN, and SiC), we obtained approximations for spectral dependences of permittivities for the ordinary and extraordinary waves. In the second part of our study (this publication), these results are used to gain insight into specific features of optical confinement in typical nitride laser heterostructures and the effect of materials of the substrate and metallic p-type electrode deposited on the laser-diode surface on this confinement. 2. OPTICAL CONFINEMENT IN LASER HETEROSTRUCTURES In this section, we consider the waveguide proper- ties of typical laser heterostructures described in avail- able publications. Since (as will be seen from what fol- lows) the substrate plays an important role in the forma- tion of an optical waveguide, the structures on the substrates of GaN, sapphire, and SiC are considered separately. 2.1. A Laser Structure on the GaN Substrate A laser heterostructure grown on the homoepitaxial GaN substrate was described by Skierbiszewski et al. [2]. This structure consists of a buffer GaN:Si layer with the thickness of 2.2 μm, an Al 0.08 Ga 0.92 N:Si emit- ter with a thickness of 550 nm, a lower GaN:Si waveguide layer with a thickness of 100 nm, a transi- tion In 0.01 Ga 0.99 N:Si layer with a thickness of 40 nm, and an active region consisting of five undoped 4-nm- thick In 0.09 Ga 0.91 N quantum wells (QWs) separated by 7-nm-thick In 0.01 Ga 0.99 N:Si barriers. The blocking 14-nm-thick In 0.01 Al 0.16 Ga 0.83 N:Mg layer is located between the active region and the 70-nm-thick upper waveguide In 0.01 Ga 0.99 N:Mg layer; then follows the p-type emitter represented by a short-period super- lattice (SL) consisting of 80 pairs of In 0.01 Ga 0.99 N/In 0.01 Al 0.16 Ga 0.83 N layers (with the thick- ness 2.5/2.5 nm) doped uniformly with Mg (the total thickness of the emitter is 400 nm). The 100-nm-thick GaN:Mg contact layer was grown on top of the p-type emitter. The level of doping of n-type layers with donors was 5 × 10 18 cm –3 , while the hole concentration measured in some p-In 0.01 Ga 0.99 N layers was 2 × 10 18 cm –3 . The experimental lasing wavelength for such structure was 408 nm. Since the period of the In 0.01 Ga 0.99 N/In 0.01 Al 0.16 Ga 0.83 N SL is much shorter than the wavelength of stimulated light, in order to sim- plify the analysis of waveguide properties of this het- erostructure, we replaced the short-period SL by a layer Optical Confinement in Laser Diodes Based on Nitrides of Group III Elements. Part 2: Analysis of Heterostructures on Various Substrates T. E. Slobodyan a , K. A. Bulashevich a, b , and S. Yu. Karpov b ^ a Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia b Soft-Impact Ltd., P.O. Box 83, St. Petersburg, 194156 Russia ^e-mail: karpov@softimpact.ru Submitted November 12, 2007; accepted for publication November 13, 2007 Abstract—Numerical simulation is used to systematically analyze the waveguide properties of laser hetero- structures based on nitrides of Group III elements and formed on substrates made of various materials (sapphire, silicon carbide, and gallium nitride); in the analysis, the birefringence effect both in the nitride structure itself and in the substrate was taken into account. The specific features of optical confinement in typical laser struc- tures and the effect of the substrate material and metallic contacts formed on top of the p-type layers are considered. The coefficients of optical losses for waveguide modes due to free charge carriers and to leakage into the substrate were estimated; these estimates were used to determine the significance of various channels of losses. PACS numbers: 78.66.Fd, 42.55.Px, 42.82.Et, 42.55.Lc DOI: 10.1134/S1063782608070166 PHYSICS OF SEMICONDUCTOR DEVICES