We report on p-n junction light-emitting diodes fabricated from MgZnO / ZnO / AlGaN / GaN triple heterostructures. Energy band diagrams of the light-emitting diode structure incorporating piezoelectric and spontaneous polarization fields were simulated, revealing a strong hole confinement near the n-ZnO / p-AlGaN interface with a hole sheet density as large as 1.82 ϫ 10 13 cm −2 for strained structures. The measured current-voltage ͑IV͒ characteristics of the triple heterostructure p-n junctions have rectifying characteristics with a turn-on voltage of ϳ3.2 V. Electron-beam-induced current measurements confirmed the presence of a p-n junction located at the n-ZnO / p-AlGaN interface. Strong optical emission was observed at ϳ390 nm as expected for excitonic optical transitions in these structures. Experimental spectral dependence of the photocurrent confirmed the excitonic origin of the optical transition at 390 nm. Light emission was measured up to 650 K, providing additional confirmation of the excitonic nature of the optical transitions in the devices.

Minority carrier diffusion length and lifetime in p-Zn 0.9 Mg 0.1 O doped with phosphorus were obtained from local electron beam irradiation measurements. The irradiation resulted in an increase of up to 25% in minority electron diffusion length from the initial value of ϳ2.12 m and in a simultaneous decrease of the peak near-bandedge cathodoluminescence intensity. The observed phenomena are attributed to charging of phosphorus-related deep acceptor level(s), which is consistent with the activation energy of 256± 20 meV found for the effect of electron injection in Zn 0.9 Mg 0.1 O.

Carrier trapping in Li-doped ZnO was studied using Electron Beam Induced Current technique, as well as cathodoluminescence spectroscopy and persistent photoconductivity measurements. Under electron beam excitation, the minority carrier diffusion length underwent a significant increase, which was correlated with growing carrier lifetime, as demonstrated by the irradiation-induced decay of CL intensity of the near-band-edge transition. Variable-temperature cathodoluminescence and photoconductivity experiments showed evidence of carrier trapping and yielded activation energies of 280 and 245 meV, respectively. These observations are attributed to the presence of a deep, Li-related acceptor state.

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Temperature dependence of the minority carrier diffusion length and lifetime in bulk n-type ZnO was studied using electron-beam-induced current and cathodoluminescence techniques. The diffusion length was observed to increase exponentially over the temperature range from 25 °C to 125 °C, yielding activation energy of 45±2meV. Concomitant decrease of the cathodoluminescence intensity for the near-band-edge transition was also observed. The activation energy determined by optical measurements was 58±7meV. The larger minority carrier diffusion length and smaller luminescence intensity are attributed to the increased lifetime of nonequilibrium holes in the valence band at elevated temperatures.