Abstract

In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Using x-ray diffraction and a diamond-anvil cell, the pressure-dependent structural properties of In2Se3 powder were studied at room temperature. α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The β phase persists upon decompression to ambient pressure. Raman spectroscopy experiments confirm this result. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure.

Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence indicates these point defects have acceptor levels 3.2, 1.4, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO 2 contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals is attributed to an acceptor, which may involve a Zn vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g ? ¼ 2.0015 and g == ¼ 2.0056, along with an isotropic center at g ¼ 2.0035. V C 2015 AIP Publishing LLC. [http://dx.

While zinc oxide (ZnO) has potential for optoelectronic applications, the lack of reliable p-type doping remains a major challenge. We provide evidence that ZnO nanocrystals contain uncompensated acceptors. IR absorption peaks at liquid-helium temperatures suggest a hydrogenic acceptor with a hole binding energy of 0.4–0.5 eV. Electron paramagnetic resonance (EPR) measurements in the dark showed a resonance at g=2.003, characteristic of acceptors that involve a zinc vacancy. An EPR resonance due to vacancy hydrogen complexes was observed after exposure to light. Given the lack of alternatives, vacancy complexes may provide a feasible route toward p-type conductivity.

Semiconductor nanocrystals have the potential for a range of applications in optoelectronics and nonlinear optics. As the surface-to-volume ratio increases, surface emission processes become more important. Using infrared (IR) and photoluminescence (PL) spectroscopy, we have developed a unified model for the acceptor and intragap surface states of ZnO nanocrystals. A PL peak was observed at 2.97 eV, in agreement with an acceptor level previously observed in the IR (Teklemichael et al 2011 Appl. Phys. Lett. 98 232112). The temperature dependence of the IR absorption peaks, which correspond to a hole binding energy of 0.46 eV, showed an ionization activation energy of only 0.08 eV. This activation energy is attributed to thermal excitation of the hole to surface states 0.38 eV above the valence band maximum. Therefore, while the acceptor is deep with respect to the bulk valence band, it is shallow with respect to surface states. A strong red PL emission centered at 1.84 eV, with an excitation onset of 3.0 eV, is attributed to surface recombination.