Indirect optical transition due to surface band bending in ZnO nanotubes

Abstract

ZnO nanotubes ͑ZNTs͒ have been successfully evolved from ZnO nanorods ͑ZNRs͒ by a simple chemical etching process. Two peaks located at 382 and 384 nm in the UV emission region has been observed in the room temperature photoluminescence ͑PL͒ spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

Low temperature near band edge recombination dynamics in ZnO nanorods

“…It is well known that both steady state PL and TRPL spectroscopies are very sensitive tools for characterizing the radiative and non-radiative recombination processes in the materials, which are very helpful in understanding the optical performance of the materials. 18 In this study, the steady state PL results clearly indicate a systematic removal of hydrogen-related donors and an evolution of other D o X lines with annealing temperature. The predominance of surface-related recombination in the case of samples annealed at lower temperatures, the suppression of this recombination channel for samples annealed above 400 C, and the enhancement in overall crystalline quality for samples annealed at around 850 C are shown and discussed in detail.…”

“…[8][9][10][11]18 The fast components extracted for the FX and the D o X emission (for the as-grown sample in the latter case) are similar to the temporal resolution of the system and therefore contain considerable uncertainty. It is clear that there is an overall trend of an increase in the bulk (slow) lifetime component for the bound excitonic emission, with the strongest effect observed following a 300 C anneal.…”

“…The fast and slow components have been associated with recombination in the "near-surface" and "bulk" regions of the sample, respectively. 3,9,10,18 It can be seen that the relative contribution of each component varies from sample to sample and from transition to transition. For the as-grown sample, the decay characteristics of the I 4 are dominated by the fast component.…”

“…In most cases, the transients exhibit a bi-exponential decay, with a characteristic fast and slow components similar to earlier reports. 3,9,10,18 The only exception is the decay of the BSF-related emission, for which the fast component could not unambiguously identified in the transients after annealing. The fast and slow components have been associated with recombination in the "near-surface" and "bulk" regions of the sample, respectively.…”

Enhancement of the photoelectrochemical properties of Cl-doped ZnO nanowires by tuning their coaxial doping profile

“…30 Charge carriers photogenerated in the bulk ZnO need to diffuse to reach the depletion layer where an electric field can drive holes to the surface. However, in bulk ZnO, the holes, the minority carriers, have short diffusion length as they rapidly recombine with electrons, the majority carriers, inside the bulk.…”