Nearest-neighbor distributions in Ga 1-x In x N y As 1-y and Ga 1-x In x N y As 1-y-z Sb z thin films upon annealing Vincenzo Lordi,* Homan B. Yuen, Seth R. Bank, Mark A. Wistey, and James S. Harris Solid State and Photonics Laboratory, Stanford University, Stanford, California 94305, USA Stephan Friedrich Advanced Detector Group, Lawrence Livermore National Laboratory, Livermore, California 94550, USA Received 19 May 2004; revised manuscript received 6 December 2004; published 15 March 2005 We examine the distribution of N-In nearest-neighbor bonds in GaInNAsSb quantum wells QWs and observe quantitatively the evolution of the distribution during thermal annealing. We use near-edge x-ray absorption fine structure to compare the behavior of compressively strained quantum wells with relaxed thick-film samples, and find no significant effect of strain on the nearest-neighbor bonding. Photoluminescence PL and electroreflectance ER spectroscopies are used to quantitatively measure the distribution of N-In nearest-neighbor states for a series of variously annealed GaInNAsSb QW samples. We find that increased annealing temperature or time leads to a blueshift of the band gap that saturates after sufficient annealing. This saturation is related to a thermodynamic equilibration of the N-In nearest-neighbor bonding in the material toward highly In-coordinated states, from an as-grown material having a nearly random bonding arrangement dominated by N-Ga bonds. The different N-In nearest-neighbor states form a fine splitting of the band gap of the material. The average spacing between these levels is found to be considerably smaller for GaInNAsSb 18 meV than for GaInNAs 35 meV. Furthermore, we present absorption measurements that reveal an increased optical efficiency of the higher In-coordinated N states that form upon annealing. Additionally, the line shape observed at room temperature in all of the spectroscopic measurements is Gaussian, indicating a strong exciton-phonon coupling in these alloys. DOI: 10.1103/PhysRevB.71.125309 PACS numbers: 78.20.Ci, 61.10.Ht, 78.67.De, 81.40.Tv I. INTRODUCTION The GaInNAs material system has received much atten- tion over the past decade for its potential use in low-cost telecommunications optoelectronic devices operating in the 1.3–1.6 μm wavelength range. 1–3 The advantages of this ma- terial system stem from its ability to be grown on GaAs substrates and the possibility for monolithic integration of highly reflective distributed Bragg reflectors, which enable the fabrication of low-cost vertical cavity lasers as well as resonant cavity detectors and modulators. These devices can be applied in high volume to address the current bottlenecks in optical networks and also to enable low-voltage optical interconnects. Recent progress on the use of GaInNAs for these applications has succeeded in producing devices oper- ating at up to 1.4 μm wavelength. 2,4 In the past few years, GaInNAsSb has been found to be a potentially superior ma- terial to GaInNAs for these applications, since higher quality material can be grown over the entire telecommunications wavelength range and particularly at the longest wavelengths that were previously unattainable. In addition, inherent ad- vantages are expected for GaInNAsSb over the competing material grown on InP InGaAsP, due to a heavier electron effective mass, better electron confinement in quantum wells, and higher differential gain. High-performance device char- acteristics have been demonstrated with GaInNAsSb for wavelengths spanning the 1.3–1.6 μm range. 5–8 Understanding the intricacies of the atomic structure and bonding in these dilute nitride materials is important for both improving the material quality and understanding the unique properties they exhibit, such as the blueshift of the band gap upon thermal annealing and the giant reduction of the band gap upon addition of small amounts of N. 9–15 We have re- cently used x-ray absorption spectroscopy XAS to directly examine the N-In nearest-neighbor bonding in thick films of Ga 0.7 In 0.3 N 0.03 As 0.97 and probe how it changes with annealing. 9 A shift in the nearest-neighbor distribution to- ward increased N-In bonding was found to occur and to cor- respond to a thermodynamic stabilization of the material as well as to the observed blueshift in the band gap. In this paper, we examine first the effect of biaxial com- pressive strain, which is present in the technologically rel- evant thin films used in optoelectronic devices, on the N-In nearest-neighbor bonding, using XAS. We find that strain does not alter the random nature of bonding in as-grown material nor does it change the atomic reconfiguration be- havior upon annealing. We also observe the N-In nearest- neighbor states in thin-film GaInNAsSb material, using vari- ous spectroscopic techniques, including photoluminescence, electroreflectance, and optical absorption. The presence of Sb a Group V element is found not to affect the N-In bond- ing to first order. With electroreflectance we are able to dis- tinguish each of the N-In nearest-neighbor states and extract bonding distributions in a series of partially annealed quan- tum well samples. Assignments of individual bonding states in the spectra are possible by using the results of the XAS experiments and ab initio band-structure calculations. We find that, like GaInNAs, as-grown GaInNAsSb material con- tains a nearly random distribution of N-In bonds, while an- nealing drives the material toward a state with increased N-In bonding and a larger band gap. The evolution of these states is monitored quantitatively during annealing. PHYSICAL REVIEW B 71, 125309 2005 1098-0121/2005/7112/1253098/$23.00 ©2005 The American Physical Society 125309-1