Highly mismatched alloys
Key researcher: S. Prucnal (s(dot)prucnal(at)hzdr.de) and Kun Gao (k(dot)gao(at)hzdr.de)
Semiconductor alloying, e.g. combining the III and V (or VI and IV) column elements, is a powerful method for obtaining materials with desired bandgaps. The common semiconductor compounds are composed of isoelectronic elements, which are relatively well matched with respect to atom size, ionicity, and electronegativity, for instance, SiGe, InGaAs, AlGaAs, InGaN….. While, high mismatched alloys are a kind of semiconductors containing isoelectronic elements with very large differences in terms of atom size, ionicity, and electronegativity, for instance, GaAsN in which N ions substitute the As sites as well as (Si,Ge)Sn alloys. These highly mismatched alloys (HMA) have very unusual and fundamentally interesting electronic/optical properties. As an example, proper alloying of (Si,Ge)Sn can result in a direct bandgap. However, HMA are generally difficult to prepare due to large miscibility gaps. Besides molecular beam epitaxy, ion implantation followed by short-time annealing presents another non-equilibrium preparation method and can be used to synthesize highly mismatched alloys. As a new class of artificial materials, HMAs are still in the experimental stages of their development. There are still a lot of unsolved questions. As an example, the research community is arguing if the “foreign” atoms are distributed as individual atoms or as clusters. A similar question also holds for ferromagnetic semiconductors.
We are working on the preparation and understanding of highly mismatched semiconductor alloys by ion beams and by comprehensive optical characterizations. The materials include N doped III-V, O doped II-IV and Sn doped Ge.
1. Temperature stable 1.3 micro-meter emission from GaAs
Fig. 1 Semilogarithmic room temperature photoluminescence spectra obtained from virgin and N or Mn implanted SI-GaAs samples after flash lamp annealing. Inset shows the schema of energy levels and radiative transitions in annealed samples.
Fig. 2 Maximum PL intensity at 1.3 micro-meter as a function of temperature obtained from virgin and N or Mn doped GaAs after flash lamp annealing.
(1) S. Prucnal, K. Gao, W. Anwand, M. Helm, W. Skorupa, S. Zhou, Temperature stable 1.3 micro-meter emission from GaAs, Optics Express, Optics Express, 20, 26075-26081 (2012).
(2) Kun Gao, S. Prucnal, W. Skorupa, M. Helm and Shengqiang Zhou, Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing, J. Appl. Phys. 114, 093511 (2013).
(3) K. Gao, S. Prucnal, R. Huebner, C. Baehtz, I. Skorupa, Y. Wang, W. Skorupa, M. Helm, S. Zhou, Ge(1-x)Sn(x) alloys synthesized by ion implantation and pulsed laser melting, Appl. Phys. Lett. 105, 042107 (2014).
(4) K. Gao, S. Prucnal, W. Skorupa, M. Helm, S. Zhou, Formation and photoluminescence of GaAs(1-x)N(x) dilute nitride achieved by N-implantation and flash lamp annealing, Appl. Phys. Lett. 105, 012107 (2014).