A zoom-in of the photo clearly shows the strong luminescence of our ZnO homojunction device. Figure 4 PL measurements of Sb-doped ZnO microrod array (red) and intrinsic ZnO microrod array (black). The inset shows a photo taken on the Sb-doped check details ZnO microrod array and a zoom-in showing violet luminescence. Figure 5 shows the temperature-dependent PL spectra of the Sb-doped ZnO microrod array from T = 30 K to T = 300 K. The red shift of the PL peak along with increasing temperature can be described by the Varshni equation : (1) where E(0) is the transition energy of the free exciton or the free electron-to-acceptor level (FA) transition at zero temperature, and α and β are constants. The result of the fitting
curve is shown in the inset
of Figure 5 with α = 7.8 × 10-4 eV/K, β = 510 K, and E(0) = 3.322 eV. Moreover, the peak of the photoluminescence can be attributed to the free electron-to-acceptor level transition [16, 20]. The acceptor binding energy is given by (2) where Eg, E_D, E_A, ϵ_0, ϵ, and r are the bandgap energy, VX-770 purchase the donor binding energy, the acceptor binding energy, the selleck chemicals llc permittivity of ZnO in vacuum, the dielectric constant of ZnO, and the distance of the electron-hole pair, respectively. The donor energy ED is reported to be about 60 meV, the value of is 30 to 60 meV, and the bandgap of ZnO is 3.437 eV; therefore, the estimated EA is 161 ± 15 meV . Strong violet luminescence at room temperature was revealed in this work. This particular phenomenon was induced by replacement of the nearly Zn sites, instead of the O ones, with Sb atoms (Sb_Zn) to form a complex with two V_Zn, which is the Sb_Zn-2V_Zn complex. This Sb_Zn-2V_Zn complex has a lower formation energy and acts as a
shallow acceptor; therefore, strong violet luminescence was induced as shown in Figure 5. From the room-temperature PL spectra shown in Figure 4, an estimation of the activation energy of 140 meV for Sb-doped ZnO was obtained. This value is in good agreement with the theoretical ionization energy of the Sb_Zn-2V_Zn complex acceptors . The particular phenomenon has a potential application in violet light emission. Figure 5 Temperature-dependent PL spectra of the Sb-doped ZnO microrod array. From top to bottom: T = 30, 45, 60, 75, 90, 105, 120, 135, 150, 180, 210, 240, 270, and 300 K, respectively. The peaks centered at around 2.8 eV are laser background signals. The inset shows the PL peak positions in energy as a function of temperature of the Sb-doped ZnO microrod array. The squares are experimental data of the FA emission, and the red line is the fitting curve to the Varshni equation. The I-V measurement of the ZnO homojunction device is shown in Figure 6. Ohmic contacts for each device were assured by the linear I-V relations shown in the inset of Figure 6. Therefore, the observed non-linear I-V characteristics as shown in Figure 6 must be due to the device rather than non-ideal electrical contacts.