As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

4.2. Test Barrier Material 47
Fig. 4.2: Cubic structure of ABO 3 pervoskite crystals.(for our analysis, A = Sr and B = Ti) (a)
shows the (100) AO-terminated plane (e.g. SrO). (b) and (c) show the (110) and (001) (TiO 2
termination) planes, respectively. Figure reprinted from [Pisk 04]
4.2 Test Barrier Material
For our purposes, we focused on a particular material Strontium Titanate SrTiO 3 to
improve our gating devices’s leakagecurrent characteristics. Reported dielectric constants
for this material is measured to be higher than that of Al x Ga 1−x As (where x is Al mole
fraction) and AlAs both at ǫ ≈ 10 - 15ǫ 0 , which comprised the n all-semiconductor gating
barrier used in the previous chapter.[Owen 09]
4.2.1 Strontium Titanate SrTiO 3 (STO)
Strontium Titanate or STO is a prototypical perovskite ferroelectric oxide has been subject
of interest due to its desirable electronic properties (e.g. large electric field-sensitive
permittivity). The perovskite crystal structure is shown in Figure 4.2. It is found to be a
Fig. 4.3: Dielectric constant ǫ for bulk STO measured with temperature. Values at 4K show
constantsintherangeof10000-20000. Thecurvesshowsampleswithdifferentcurrentdirections
(E) and stresses (τ for strain and σ for thermal strain) Figure reprinted from [Mull 79].