Mutual Passivation in Dilute GaN x As 1-x Alloys
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Mutual Passivation in Dilute GaNxAs1-x Alloys K. M. Yu 1, W. Walukiewicz 1, J. Wu 2, D. E. Mars 3, M. A. Scarpulla 1,4, O. D. Dubon 1,4, M. C. Ridgway 5, and J. F. Geisz 6 1
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Dept. Chemistry and Chemical Biology, Harvard University, Cambridge, MA 3 Agilent Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94304 4 Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 5 Australian National University, Canberra, Australia 6 National Renewable Energy Laboratory, Golden, Colorado 80401 2
ABSTRACT The dilute GaNxAs1-x alloys (with x up to 0.05) have exhibited many unusual properties as compared to the conventional binary and ternary semiconductor alloys. We report on a new effect in the GaNxAs1-x alloy system in which electrically active substitutional group IV donors and isoelectronic N atoms passivate each other’s activity. This mutual passivation occurs in dilute GaNxAs1-x doped with group IV donors through the formation of nearest neighbor IVGaNAs pairs when the samples are annealed under conditions such that the diffusion length of the donors is greater than or equal to the average distance between donor and N atoms. The passivation of the shallow donors and the NAs atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental bandgap. This mutual passivation effect is demonstrated in both Si and Ge doped GaNxAs1-x alloys. Analytical calculations of the passivation process based on Ga vacancy mediated diffusion show good agreement with the experimental results.
INTRODUCTION In recent years we witnessed the emergence of a new class of semiconductor alloys, the highly mismatched alloys (HMAs) which exhibit an unusually large band gap bowing. In these HMAs only a small amount of more electronegative elements (typically from less than 1% to several % ) substituting the metallic anion of the III-V or II-VI matrix semiconductors results in large modification in the conduction band structure of the alloys. The most notable and well studied example is GaNxAs1-x, in which strong band gap bowing by as much as 180 meV per mole percent of N (i.e. for x=0.01) has been observed [1-4]. Comparably large band gap reductions have also been observed in other III-Nx-V1-x alloys such as GaInNAs, GaNP, InNP and AlGaNAs [4-9]. The strong dependence of the band gap on the N content has made these dilute III-V nitrides important materials for a variety of applications [10-13]. Theoretical and experimental aspects of the III-N-V alloys were extensively investigated and have been reviewed recently in a series articles [14-17]. In close analogy, the formation of group II-O-VI HMAs by partial substitution of group VI anions with electronegative O in II-VI compounds has also been recently demonstrated [18].
E8.1.2
Several theoretical studies have addressed the unusually strong dependence of the fundamental gap on the N content in the group II
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