Y.P. Qiao

A top-emission organic light-emitting diode with a silicon anode and an Sm/Au cathode

A top-emission organic light-emitting diode (TEOLED) with a p-type silicon anode and a semitransparent samarium/gold cathode has been constructed and studied. With a structure of Al∕p-Si∕SiOx∕N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine(NPB)∕Tris-(8-hydroxyquinoline)aluminum(Alq)∕LiF∕Al, we have found that compared to indium-tin-oxide, the p-Si anode enhances the unbalance between electron- and hole-injection, which is a disadvantage factor for the light-emitting efficiency of the TEOLED. Selecting p-Si wafers with suitable electric resistivities and inserting an ultrathin low temperature grown SiOx layer of about 1.5nm between the anode and NPB can effectively restrict hole-injection. Moreover, a low work function Sm∕Au cathode was used to enhance electron-injection. The electroluminescence efficiency of the TEOLED depends on the thickness of the Sm layer in the cathode. A current efficiency of 0.55cd∕A and a power efficiency of 0.07lm∕W have been reached.

An effect of Si nanoparticles on enhancing Er3+ electroluminescence in Si-rich SiO2:Er films

Er-doped Si-rich SiO2 (SRSO:Er) films have been deposited on n(+)-Si substrates by the magnetron sputtering technique, and both photoluminescence (PL) and electroluminescence (EL) at 1.54 mum have been observed from the films at room temperature. Dependence of pi, and EL intensities on the excess-Si content and annealing temperature has been studied. It is found that proper Si content and annealing temperature can evidently enhance EL intensity. An SRSO:Er film with 20% excess Si (area ratio of the Si target to the whole target) had more intense EL than a SiO2:Er film without excess Si, both annealed at 800 degreesC, by a factor of 5. This fact clearly demonstrates that energy coupling between Si nanometer particles and Er3+ ions also exists in the EL process as well as in the PL process. Experimental results also indicate that crystallization is not a prerequisite for NSPs enhancing luminescence in SRSO:Er films. The PL and EL spectra of the SRSO:Er films have much broader full widths at half maximum (FWHM, similar to 60 nm) than those of the other Er-doped materials reported. This wide FWHM can perhaps be used in wavelength division multiplexing in optical communication in future

Improving charge-injection balance and cathode transmittance of top-emitting organic light-emitting device with p-type silicon anode

Both charge-injection balance and high transmittance for the cathode are important to achieve high electroluminescence (EL) efficiency for a top-emitting organic light-emitting device (TEOLED) fabricated on silicon substrate. In this letter, by optimizing the electrical resistivity of the p-type silicon chip used as the anode and applying a Yb/Au double layer cathode with high electron-injection property and high transmittance, the TEOLED with a configuration of p-type silicon/thermal grown SiO2/NPB/Alq(3)/Yb/Au exhibits a higher EL efficiency than those of the TEOLEDs each with a Si chip as the anode reported previously. Its current efficiency is almost equal to that of a TEOLED with the same configuration except for an indium tin oxide anode. (c) 2005 American Institute of Physics.

Room-temperature 1.54-μm electroluminescence from Er-doped Si-rich SiO2 films deposited on p-Si by magnetron sputtering

Abstract Er-doped Si-rich SiO 2 (SRSO:Er) films with excess silicon contents of 0, 10, 20 and 30% were deposited on p-Si substrates using the magnetron sputtering technique, and then Au/SRSO:Er/p-Si light-emitting diodes (LEDs) were fabricated after the SRSO:Er/p-Si samples were annealed separately at 600, 700, 800, 900 and 1000 °C. Room temperature 1.54-μm electroluminescence (EL) from the Au/SRSO:Er/p-Si LEDs was observed when the forward bias was above 4 V. It was found that excess silicon with a proper content in a SRSO:Er film annealed at a suitable temperature can evidently enhance EL intensity of the LED made of the film. The optimum annealing temperatures for enhancing EL intensity were 900, 900, 800 and 700 °C for the SRSO:Er films containing 0, 10, 20 and 30% excess silicon, respectively. The 1.54-μm EL intensity of the Au/SRSO:Er/p-Si LED made of a SRSO:Er film with 20% excess silicon being annealed at 800 °C was the most intense.

Organic light-emitting diodes with n-type silicon anode

In an AIQ-based bilayer organic light-emitting diode, n-type silicon has been used as an anode, and semitransparent metals Sm (15 nm)/Au (15 nm) as a cathode. This device has much smaller currents at high voltages (> 8 V) and a higher turn-on voltage than the device with an identical structure but an indium-tin oxide anode. By successively depositing ultra thin films of Au and AIQ on the n-Si surface, the device performances are improved significantly, reaching a power efficiency of 0.1 Im W-1 and a current efficiency of 0.7 cd A(-1) at 15.9 V and 0.3 mA mm(-2). The mechanisms for the hole injection and performance improvement are discussed.

Blue to red electroluminescence from Au/native silicon oxide/p-Si structure subjected to rapid thermal annealing

Blue, green, yellow and red electroluminescence (EL) from the semitransparent Au/native silicon oxide (NSO)/p-Si structure was observed. The p-Si wafers with NSO films were subjected to rapid thermal annealing (RTA) at a series of temperatures between 600 and 1000°C and then the semitransparent Au/NSO/p-Si structure was made. Under forward biases over 3 V, strong EL could be observed. The effect of RTA temperature on EL spectra of the semitransparent Au/NSO/p-Si structure was studied. It was found that with increasing RTA temperature from 600 to 900°C, wavelength of the main EL peak varied between 460 and 680 nm and intensity of the main EL peak increased monotonously.

Hole-injection mechanisms of organic light emitting diodes with Si anodes

We have studied the hole-injection mechanisms of two types of Si anodes, polycrystalline Si (poly-Si) film and crystal Si (c-Si) wafer anodes, in organic light emitting diodes (OLEDs) and those of OLEDs with indium tin oxide anodes. It was found that the hole-injection mechanisms of these devices are very different from each other. The hole injection of the c-Si anode obeys the classic Richardson thermionic emission model and that of the poly-Si film anode agrees well with the modified thermionic emission model (Scott and Malliaras 1999 Chem. Phys. Lett. 299 115-9). When the c-Si anode is covered with a thin SiO2 layer, its hole injection changes to obey the modified thermionic emission model.

Room-temperature luminescence at 1.54 μm and other wavelengths from Er-doped Si-rich Si oxide

SiO2:Si:Er films were deposited on n+-Si substrate using the magnetron sputtering technique, and then Au/ SiO2: Si:Er /n+-Si diodes were fabricated. Both Er3+ photoluminescence (PL) from the SiO2: Si: Er/n+-Si and electroluminescence (EL) from the Au/SiO2: Si: Er /n+-Si diodes were studied. The 1.54 micrometers PL intensity ratio of SiO2: Si: Er/n+-Si to that of the SiO2: Er/n+-Si measured under identical conditions can be as large as ~30. While the 1.54 micrometers EL intensity ratio of an Au/ SiO2:Si:Er/n+-Si diode to that of an Au/SiO2:Er/n+-Si diode measured under identical conditions can be as large as 6. We also deposited nanoscale (SiO2:Er/Si(1.0~4.0nm)/SiO2:Er) sandwich structure, in which the silicon layer between the two SiO2:Er barriers was 1.0~4.0 nm thick with an interval of 0.2 nm, on both n+-Si and p-Si substrates. Each EL spectrum of the Au/nanoscale (SiO2:Er/Si/SiO2:Er)/n+-Si diodes can be fitted by three Gaussian bands with peak energies of 0.757 eV (1.64 micrometers ), 0.806 eV (1.54 micrometers ) and 0.860 eV (1.44 micrometers ), and full widths at half maximum of 0.052, 0.045 and 0.055 eV, respectively. Among the Au/nanoscale (SiO2:Er/Si/SiO2:Er)/n+-Si diodes with the Si layers having various thicknesses, the EL intensities of the 1.64, 1.54 and 1.44 micrometers bands of the diode with a 1.6 nm Si layer attain maxima which are 22, 8 and 7 times larger than those of the control diode without any Si layer (Au/nanoscale SiO2:Er/n+-Si), respectively.