Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5–20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive VGa-Hn complexes that can be activated by H removal during low energy electron irradiation.

We present systematic studies of magnetic and transport properties of ${\text{Zn}}_{1-x}{\text{Mn}}_x{\text{GeAs}}_2$ semimagnetic semiconductor with the chemical composition varying between $0.053\le x\le 0.182$ . The transport characterization showed that all investigated samples had $p$ -type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations $p\ge {10}^{19}{\text{cm}}^{-3}$ and relatively low mobilities, $\mu \le 15{\text{cm}}^2/\left(\text{V}\text{s}\right)$ , also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with $x\ge 0.078$ . We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains.

We investigated the nature of the magnetic phase transition in Ge1$-${}x$-${}ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083$\le${}x$\le${}0.142 and 0.012$\le${}y$\le${}0.119. The dc magnetization measurements performed in magnetic fields up to 90 kOe and temperature range 2\char21{}200 K showed that the magnetic ordering at temperatures below T=50$\hskip0.3em${}K exhibits features characteristic for both spin-glass and ferromagnetic phases. The modified Sherrington-Southern model was applied to explain the observed transition temperatures. The calculations showed that the spin-glass state is preferred in the range of the experimental carrier concentrations and Mn contents. The value of the Mn hole exchange integral was estimated to be Jpd=0.45\ifmmode\pm\else\textpm\fi{}0.05$\hskip0.3em${}eV. The experimental magnetization vs temperature curves were reproduced satisfactorily using the noninteracting spin-wave theory with the exchange constant Jpd values consistent with those calculated using modified Sherrington-Southern model. The magnetization vs magnetic field curves showed nonsaturating behavior at magnetic fields B<90$\hskip0.3em${}kOe indicating the presence of strong magnetic frustration in the system. The experimental results were reproduced theoretically with good accuracy using the molecular-field-approximation-based model of a disordered ferromagnet with long-range Ruderman-Kittel-Kasuya-Yosida interaction.