Wurtzite Zn1−xMgxO thin films with Mg contents between x=0 and x=0.37 were grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy using a MgO/ZnMgO buffer layer. The a-lattice parameter is independent from the Mg concentration, whereas the c-lattice parameter decreases from 5.20 Å for x=0 to 5.17 Å for x=0.37, indicating pseudomorphic growth. The near band edge photoluminescence shows a blueshift with increasing Mg concentration to an emission energy of 4.11 eV for x=0.37. Simultaneously, the energetic position of the deep defect luminescence shows a linear shift from 2.2 to 2.8 eV. Low temperature transmission measurements reveal strong excitonic features for the investigated composition range and alloy broadening effects for higher Mg contents. The Stokes shift as well as the Urbach energy is increased to values of up to 125 and 54 meV for x=0.37, respectively, indicating exciton localization due to alloy fluctuations.

We report ferromagnetic resonance experiments on Ga1−xMnxAs thin films. For the dc magnetic field perpendicular to the sample plane, we observe up to eight distinct resonances, which we attribute to spin wave modes. To account for the spacing of the resonances, we infer a linear gradient in the magnetic properties, which is ascribed to a linear variation of the uniaxial magnetic anisotropy with film thickness. Values of D=(1±0.4)×10−9 Oe cm2 for the spin stiffness and JMnMn≈1 meV for the exchange integral between Mn spins are obtained.

We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.