Y. T. Shih

Ultraviolet Electroluminescence From n-ZnO–SiO

Ultraviolet (UV) light-emitting diodes composed of n-ZnO:Al-SiO2-ZnO nanocomposite/p-GaN:Mg heterojunction were fabricated on the (0002) Al2O3 substrate. A SiO2 layer embedded with ZnO nanodots was prepared on the p-type GaN using spin-on coating of SiO2 nanoparticles together with atomic layer deposition (ALD). An n-type Al-doped ZnO layer was deposited also by ALD. The SiO2-ZnO nanocomposite layer accomplishes a role of the current blocking layer and also causes, by its low refractive index, the increase in the light extraction efficiency from n-ZnO. Significant UV electroluminescence from n-ZnO was achieved at a low forward-bias current of 1.8 mA. Strong UV emission arising from impact ionization in GaN, ZnO, and GaN:Mg states was also observed at reverse breakdown bias.

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Thin Al2O3 surface-passivating layers grown by atomic layer deposition at 100°C were demonstrated to be instrumental in producing efficient light emission from silicon. External quantum efficiency up to 1.3×10−4 was observed from silicon metal-insulator-semiconductor light-emitting diodes with a 5nm Al2O3 surface-passivating layer as the insulator, which is more than tenfold that from similar devices with a 5nm SiO2 insulator layer thermally oxidized at 1000°C. Anomalous temperature dependences of the photoluminescence intensities and spectra at low temperatures indicate the presence of bound excitonic traps at the Al2O3∕Si interface. The enhanced light emission may be attributed to the temporary capture of excitons by the interfacial bound excitonic traps, which effectively reduces nonradiative recombination.

–ZnO Nanocomposite/p-GaN Heterojunction Light-Emitting Diodes at Forward and Reverse Bias

Si nanocrystals embedded in a SiO2 matrix and an n-type Al-doped ZnO (ZnO:Al) layer were applied to improve the external quantum efficiency from Si in n- ZnO/SiO2-Si nanocrystals-SiO2/p-Si heterojunction light-emitting diodes (LEDs). The Si nanocrystals were grown by low pressure chemical vapor deposition and the ZnO:Al layer was prepared by atomic layer deposition. The n-type ZnO:Al layer acts as an electron injection layer, a transparent conductive window, and an anti-reflection coating to increase the light extraction efficiency. Owing to the spatial confinement of carriers and surface passivation by the surrounding SiO2, the Si nanocrystals embedded in the SiO2 matrix lead to a significant enhancement of the light emission efficiency from Si. An external quantum efficiency up to 4.3 x 10(-4) at the wavelength corresponding to the indirect bandgap of Si was achieved at room temperature.

Enhancement in the efficiency of light emission from silicon by a thin Al2O3 surface-passivating layer grown by atomic layer deposition at low temperature

We fabricated and characterized ultraviolet (UV) light-emitting diodes (LEDs) composed of <i>n</i>-ZnO/SiO₂-ZnO nanocomposite/<i>p</i>-GaN heterostructures. Significant UV electroluminescence at 387 nm from the <i>n</i>-ZnO layer in this heterostructure LED was observed at a forward-bias current of as low as 1.8 mA. This is ascribed to the high quality of the <i>n</i>-ZnO layer and the effective function of the SiO₂-ZnO nanocomposite layer. The SiO₂-ZnO nanocomposite layer accomplishes the role of current blocking by forming the larger energy barrier for electron injection from <i>n</i>-ZnO into <i>p</i> -GaN and also contributes to, due to its low refractive index, higher light extraction efficiency from the <i>n</i>-ZnO layer.

An efficient Si light-emitting diode based on an n- ZnO/SiO2–Si nanocrystals-SiO2/p-Si heterostructure

P-type phosphorus-doped ZnO (ZnO:P) films were fabricated by atomic layer deposition of ZnO upon the amorphous silica substrates, which were prepared by coating the spin-on dopant consisted of P 2 O 5 and SiO 2 on silicon wafers. Post-deposition thermal treatments were carried out to diffuse the phosphorus dopants into ZnO and to activate the phosphorus-related acceptor states. The ZnO:P films exhibited p-type conductivity with an average hole concentration of 1.05 x 10 17 cm -3 . Significant spectral peaks associated with the acceptor states appeared in the low-temperature photoluminescence spectra of the p-type ZnO:P films. Optically-pumped stimulated emission around 393 nm was observed at room temperature, thereby indicating a good optical quality of the p-type ZnO:P film.

Structure and Ultraviolet Electroluminescence of

Highly oriented zinc oxide (ZnO) films accompanied by stimulated emission have been fabricated on amorphous alkaline earth boro-aluminosilicate glass substrates by atomic layer deposition (ALD). By introducing a buffer layer which was deposited at a high temperature of 300°C and followed by postdeposition rapid thermal annealing at 800°C, ZnO films with the (0001) preferred orientation could be grown by ALD upon the buffer layer at a low temperature of 150°C. Photoluminescence exhibited a dominant near-band-edge spontaneous emission at 380 nm and a negligible defect-related band. Optically pumped stimulated emission around 395 nm with a threshold intensity of 38.1 kW/cm 2 was observed at room temperature, which is ascribed to the good optical and crystal quality of the ZnO films grown by the ALD technique on the amorphous glass substrates.