Band-edge emission of undoped and doped ZnO single crystals at room temperature

Abstract

Band-edge emission of ZnO at around room temperature was investigated by measuring the temperature dependence of cathodoluminescence spectra at 20–300 K. Undoped crystals grown by a vapor transport method and Al-doped crystals by flux method were employed to elucidate the effect of doping on luminescence properties. For the Al-doped crystals, the free-exciton emission was weak through out the temperature range T<300 K. The most intense emission peak of the Al-doped crystal was energetically close to bound exciton annihilation emission. On the other hand, for undoped crystals, it was found that the most intense emission peak at room temperature was at E≈Eg−60 meV and this peak was not assignable to free-exciton annihilation emission. It was also found that this peak is not a reason for the reduction in emission efficiency.

Near-band-edge slow luminescence in nominally undoped bulk ZnO

“…This result has been previously reported in cathodoluminescence by other authors. 9 This behavior for the 3.238-, 3.166-, and 3.094-eV lines up to 200 K suggests that these lines can be assigned to vibronic transitions occurring at the same center. We also point out that the timeresolved spectra of the 3.238-eV line and its LO-phonon replicas are always slightly shifted to lower energies than the steady-state PL.…”

“…Understanding the fundamental emission processes near the semiconductor band edge is of particular importance for applications of this oxide semiconductor in device emitters and light detectors for the ultraviolet and visible spectral region. [1][2][3][4][5][6][7][8][9] At low temperatures the near-band-edge steady-state photoluminescence ͑PL͒ spectra of ZnO single crystals grown by seeded chemical-vapor transport ͑SCVT͒ is dominated by the donor bound exciton ͑BE͒ lines. [1][2][3][4][5][6][7] The relative intensities of these BE lines is highly dependent on the growth process and the presence of impurities such as H, Al, Ga, and In, as well as postgrowth annealing treatments.…”

Production and recovery of defects in phosphorus-implanted ZnO

“…For the unimplanted ZnO, there is a band-edge ultraviolet (UV) emission peak located at 3.3 eV, which is due to the recombination of free excitons. 2,[39][40][41] The deep level emission is rather weak and nearly invisible. Either there are few deep level centers, or there are nonradiative recombination centers that have suppressed the deep level emission.…”

Nature of room-temperature photoluminescence in ZnO

“…[1][2][3] Despite many years of extensive studies [4][5][6][7][8][9][10][11][12] some of the fundamental properties of the luminescence in ZnO are still not fully understood. One of the poorly understood issues is the origin of the room temperature photoluminescence (PL) structure.…”