IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 8, NO. 4, JULY/AUGUST 2002 787 Strain-Compensated GaInNAs Structures for 1.3- m Lasers Tomi Jouhti, Chang Si Peng, Emil-Mihai Pavelescu, Janne Konttinen, Luis Aguiar Gomes, Oleg G. Okhotnikov, and Markus Pessa Invited Paper Abstract—GaAs-based dilute nitride lasers are potential light sources for future optical fiber communication systems at the wavelength of 1.3 m. In this paper we discuss the results of studies of optimization of the growth conditions and active regions of the GaAs-based lasers. To this end, a series of samples were grown using the molecular beam epitaxy technique. The active regions consisted of quantum wells, strain-compensating layers, and strain-mediating layers. They were characterized by photo- luminescence and double crystal X-ray diffraction methods. The optical properties were very much affected by a choice of growth conditions, details of the quantum wells, and postgrowth thermal treatment. Preliminary results on diode-pumped vertical-cavity surface emitting lasers, which launch light power of 3.5 mW coupled into a single-mode fiber, are also presented. Index Terms—GaInNAs, semiconductor laser, molecular beam epitaxy. I. INTRODUCTION G aAs-BASED dilute nitride alloys are seen to challenge now dominating InP-based semiconductors in the 1.3- m transmitter markets. GaAs would offer many advantages over InP. It would be cost-effective and robust and have higher thermal conductivity than InP, and would allow for the man- ufacture of monolithic vertical-cavity surface-emitting lasers (VCSELs) in a single epitaxial growth run. Basically, GaAs holds all the possibilities to reach light emis- sion at 1.3 m with only one decisive point missing—an easy way to do it. At first sight it seems that the long-wavelength limit for GaInAs quantum wells (QWs) on GaAs substrates is about 1.2 m [1], [2]. Alloying more indium with GaAs longer wavelengths can be reached, but too high strain is generated and misfit dislocations are inevitably formed. Several new routes are being investigated to reach m. One of them is the use of GaInAs–GaAs self-assembled quantum dots, which pro- duce light at 1.3 m [3], but homogeneity in the dot density and size as well as reproducibility of the wafers hinder volume production of this material at the moment. Secondly, 1.3- m GaAsSb–GaAs QWs have been demonstrated despite uncertain- Manuscript received April 25, 2002; revised June 4, 2002. This work was supported by the Technology Development Centre (Tekes), by the Academy of Finland, by the Pirkanmaa TE-Centre, and by industrial partners. The authors are with the Optoelectronics Research Centre, Tampere Univer- sity of Technology, FIN-33101 Tampere, Finland. Digital Object Identifier 10.1109/JSTQE.2002.801671. ties about their band offsets at heterojunctions, which make it hard to design the active region of the lasers [4], [5]. Both these approaches require layers that are under very high compressive strain. The third possibility, discussed in this paper, is the use of mixed group-III dilute nitrides, or substitutionally disordered Ga In N As [6]. These alloys possess intriguing phys- ical properties and great potential for applications in optoelec- tronics. GaInNAs–GaAs edge-emitting QW lasers have already been demonstrated by many researchers, see, e.g., [7]–[9]. Optically and electrically pumped monolithic VCSELs have also been demonstrated, and the first commercial VCSELs will probably be in pilot production later this year [10]–[13]. In this paper, we report on our latest results obtained in attempts to optimize 1.3- m GaInNAs–GaAs QW heterostruc- tures. We also report on lasers made of this material. The GaInNAs–GaAs material system is presented in Section II. Details of epitaxial growth are given in Section III. In Section IV, GaNAs strain-compensating layers (SCLs) and GaInNAs strain-mediating layers (SMLs) are studied. In Section V, effects of postgrowth annealing on material properties are ex- plored. In Section VI, we present a high-power photo-pumped GaAs VCSEL at 1.3 m. II. GaInNAs–GaAs MATERIAL SYSTEM The negative energy-band bowing of the GaAs–GaN alloy makes it possible to expand the spectral range of GaAs to m [14]. Alloying indium with GaAs decreases the bandgap and yields biaxial compressive strain in GaInAs. Alloying nitrogen with GaInAs reduces both the bandgap and lattice strain in Ga In N As –GaAs (lattice matching at ), yielding a “type-I” band discontinuity, which is favorable for lasing action. In other words, the degree of strain and the bandgap are controlled by and as long as the layer thickness lattice strain product remains below a critical limit of the onset of misfit dislocations. The conduction band offset at GaInNAs–GaAs becomes large ( 400 meV), providing good electron confinement. This fact together with a nitrogen-related improvement in temperature insensitivity of the lowest electron confined level give rise to a high characteristic temperature of the laser [9], [14]. 1077-260X/02$17.00 © 2002 IEEE