Multicolor light-emitting devices with Tb2O3 on silicon

Great efforts have been devoted to achieving efficient Si-based light-emitting devices. Here we report new light-emitting devices fabricated with Tb2O3 on Si substrates. Intense green electroluminescence was observed, with a turn-on voltage of about 8 V. The green emission is attributed to the characteristic transitions of Tb3+ ions in Tb2O3. The electroluminescence mechanisms of the Tb2O3 light-emitting devices are discussed. In addition, visible and near infrared electroluminescence was observed in rare-earth (Eu3+, Sm3+ and Yb3+) doped Tb2O3 light-emitting devices.

the forward bias is 20 V, while the reverse leakage current is minimal. These results show that the Tb 2 O 3 LED has excellent rectification performance.
The EL mechanism is schematically illustrated in the inset of Fig. 3. When a sufficiently high forward bias is applied, the energy bands of both Tb 2 O 3 and SiO x bend upward along the electric field direction. According to Zhu et al. [21][22][23] , a trap-assisted tunneling (TAT) mechanism dominates the conduction mechanism at the EL-enabling voltages. When a sufficiently high forward bias voltage is applied between the two electrodes, a large number of electrons in Si accumulate in Si/SiO x interface and then reach the conduction band of Tb 2 O 3 by   We have demonstrated a bright green EL device based on Tb 2 O 3 . To further explore the possibility of using Tb 2 O 3 as a host material to RE ions to achieve devices of other colors, we further fabricated EL devices with RE-doped Tb 2 O 3 . Intense red EL is observed from Eu 3+ doped Tb 2 O 3 LED. As shown in Fig. 4(a), the emission peaks are at about 582, 619, 646, and 694 nm, corresponding to 5 D 0 -7 F J (J = 1, 2, 3, and 4) transitions of Eu 3+ . The highest peak at 619 nm corresponds to the Eu 3+ electric dipole transitions of 5 D 0 -7 F 2 17 . In Fig. 4(b), strong orange EL is observed from Sm 3+ doped Tb 2 O 3 LED. The characteristic of the 4 G 5/2 -6 H J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm 3+ ions are appeared. The Sm 3+ emission peaks are from transitions of 4 G 5/2 -6 H 5/2 (558 nm), 4 G 5/2 -6 H 7/2 (593 nm), 4 G 5/2 -6 H 9/2 (640 nm), and 4 G 5/2 -6 H 11/2 (701 nm) 18 . In Fig. 4(c), both green emission of Tb 3+ and near IR emission of Yb 3+ are obtained. The characteristic peak of Yb 3+ is attributed to the transition from 2 F 5/2 to 2 F 7/2 19 . As shown in Fig. 4(d), The CIE coordinates of the green-, red-and orange-emitting devices are (0.33, 0.61), (0.60, 0.39) and (0.51, 0.48), respectively.
In summary, new LEDs from Si-based Tb 2 O 3 are fabricated. Intense green EL was observed, with a turn-on voltage of about 8 V. The green emission centered at 484, 540, 582, and 616 nm, corresponding to the 5 D 4 -7 F J transitions of Tb 3+ in Tb 2 O 3 , where J = 6, 5, 4, and 3. The EL intensity increases with the applied voltage up to 20 V. In addition, red, orange, and near infrared EL were observed from RE 3+ (Eu 3+ , Sm 3+ and Yb 3+ ) doped Tb 2 O 3 LEDs, respectively. Our results could provide a possible route for achieving stable and highly efficient Si-based LEDs.

Methods
About 200 nm Tb 2 O 3 films and RE-doped Tb 2 O 3 films were deposited on n-type Si (100) substrates by magnetron co-sputtering technique. The Si substrates were cleaned by dipping in a dilute HF solution (HF:H 2 O = 1:7) for 60 s. Tb (99.95%) target was sputtered in Ar:O 2 = 15:5 atmosphere, at a substrate temperature of 150 °C. The deposition rate was 0.4 Å/s. RE ions (RE = Sm, Eu, and Yb) were doped in Tb 2 O 3 films by sputtering with Sm (99.95%), Eu (99.95%) and Yb (99.95%) targets, respectively. Ga 2 O 3 layer (~20 nm) was deposited by sputtering with Ga 2 O 3 target. The as-deposited samples were annealed in O 2 ambient at 500, 600, or 700 °C for 1 hour, respectively. We fabricated the LEDs as schematically illustrated in the inset of Fig. 2. ITO and Ag electrodes were deposited on the surface of the film and the back side of the Si substrate, respectively, both by magnetron sputtering.
The crystal structure characterization was carried out by using Bruker D8 ADVANCE XRD with Cu-Ka radiation, and the morphology of the samples was determined by TEM (Hitachi, H8100 200 kV). The EL spectra of the devices and I-V characteristics were measured by a system of an ACTON 150 CCD spectrometer and a Keithley 2410 source meter, respectively.