Steady-state and dynamic characteristics of deep UV luminescence in rock salt-structured MgxZn1−xO

Abstract

Temperature-dependent cathodoluminescence spectra were measured for rock salt-structured MgxZn1−xO films with x = 0.95–0.61. The Mg0.95Zn0.05O film exhibited the shortest deep UV peak wavelength of 199 nm (6.24 eV) at 6 K. Relatively high equivalent internal quantum efficiencies of 0.9%–11% were obtained. The Tauc plots, which were obtained from temperature-dependent optical transmittance measurements, exhibited large Stokes-like shifts of 0.7–0.9 eV at 6–300 K. Time-resolved photoluminescence (PL) signals at 7 K exhibited fast and slow decay components. The fast decay component had PL lifetimes of 2.59–3.08 ns, and the slow decay component far exceeded the measurement time range of 12.5 ns. The fast decay constant reflected the transfer lifetime of the photoexcited carriers to certain trapping centers. These centers were tentatively ascribed to Zn-related isoelectronic trapped-hole centers and may be a cause of the large Stokes-like shifts. The signals at 300 K exhibited very short PL lifetimes of 120–180 ps. The PL lifetimes were mainly attributed to the nonradiative recombination lifetime. Simultaneous decreases in the Zn-related isoelectronic trapped-hole centers and the nonradiative recombination centers were found to be necessary to improve the DUV emission properties of RS-MgxZn1−xO films.

Realization of cathodoluminescence in the 180 nm spectral range by suppressing thermal stress in mist chemical vapor deposition of rocksalt-structured MgZnO films

“…These observations demonstrate the realization of NBE emission in the 180-190 nm spectral range at 300 K. The equivalent internal quantum efficiency eq int h for the NBE emission peak is defined as spectrally integrated CL intensity at 300 K divided by that at 6 K, and the values are 4.4%, 1.9%, 2.7%, and 5.3% for x = 0.92, 0.82, 0.73, and 0.65, respectively. The E g values at 6 and 300 K, which were obtained using optical transmittance and reflectance measurements in our previous studies, 19,24,27) are plotted, respectively, by blue and red open circles in Fig. 9.…”

“…The values drastically decreased compared to those (0.7-0.9 eV) in our previous reports. 23,25,27) The postgrowth slow-cooling process was found to be crucial to improve the VUV and DUV emission characteristics in RS-Mg x Zn 1−x O alloys.…”

“…[21][22][23] Observation of DUV cathodoluminescence (CL) in the 199-250 nm spectral range was demonstrated. [21][22][23][24][25][26][27] However, large Stokes-like shift, which is defined as the energy difference between E g and CL peak energy, was observed to be as large as 0.7-0.9 eV. 27) The E g fluctuation induced by differences in the local arrangements of Mg and Zn atoms in the RS-Mg x Zn 1−x O alloy 20,24) or the formation of Zn-related isoelectronic trappedhole centers 27) may be the cause of the large Stokes-like shift.…”

Bandgap engineering of spinel-structured oxide semiconductor alloys

“…MgAl 2 O 4 has a large bandgap (∼7.8 eV) and good mechanical, chemical, and optical properties [21]. In particular, because the bandgap and optical properties are similar to those of MgO [22], bandgap engineering, such as Mg-rich MgZnO alloys, can be expected [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. However, these ultra-wide bandgap (UWBG) oxide materials still face challenges with regard to ambipolar doping [37][38][39].…”