Changes in optical properties of MnAs thin films on GaAs(001) induced by α- to β-phase transition

✍ Scribed by Gallas, B. ;Rivory, J. ;Arwin, H. ;Vidal, F. ;Etgens, V. H.

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 292 KB
• Volume: 205
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/pssa.200777782

✦ Synopsis

Abstract

MnAs layers with 45 nm thickness were grown epitaxially on GaAs(001) substrates. Ellipsometry measurements were made in the spectral range 0.045 eV to 6 eV as a function of temperature (between –10 °C and 50 °C) at 70° of incidence. In this way the transition from the hexagonal α‐phase to the orthorhombic β‐phase could be monitored. Non‐zero off‐diagonal elements of the Jones matrix for an azimuth of 38° off the [1$ \bar 1 $0] axis of the substrate indicate that the optical functions of MnAs are anisotropic in both phases. The optical conductivity exhibits low‐energy interband transitions around 0.3 eV, more clearly seen in the α‐phase than in the β‐phase. Extrapolation of the optical conductivity to zero frequency confirms that the α‐phase is about two times more conducting than the β‐phase. A broad structure is observed in the visible range around 3 eV. The α‐phase is characterised by an anisotropy induced energy difference of this structure with a maximum at 2.8 eV for the extraordinary index and at 3.15 eV for the ordinary index. This difference vanishes in the β‐phase in which anisotropy mainly induces changes in amplitude of the 3 eV structure. The assignment of the structures will be discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)