The distinct visible electroluminescence (EL) at room temperature has been realized based on n-ZnO∕p-Si heterojunction. The EL peak energy coincided well with the deep-level photoluminescence of ZnO, suggesting that the EL emission was originated from the radiative recombination via deep-level defects in n-ZnO layers. The transport mechanisms of the diodes have been discussed with the characteristics of current-voltage (I-V) and light-output–voltage (L-V), in terms of the energy band diagram of ZnO∕Si heterojunction. The tunneling mechanism via deep-level states was the main conduction process at low forward bias, while space-charge-limited current conduction dominated the carrier transport at higher bias. Light-output–current (L-I) characteristic of the diode followed a power law such as L∼Im, which showed a superlinear behavior at low injection current and became almost linear due to the saturation of nonradiative recombination centers at high current level.
We report on the realization of ZnO homojunction light-emitting diodes (LEDs) fabricated by metalorganic chemical vapor deposition on (0001) ZnO bulk substrate. The p-type ZnO epilayer was formed by nitrogen incorporation using N2O gas as oxidizing and doping sources. Distinct electroluminescence (EL) emissions in the blue and yellow regions were observed at room temperature by the naked eye under forward bias. The EL peak energy coincided with the photoluminescence peak energy of the ZnO epilayer, suggesting that the EL emissions emerge from the ZnO epilayer. In addition, the current-voltage and light output-voltage characteristics of ZnO homojunction LEDs have also been studied.
n - Zn O ∕ Si O x ∕ n - Si and n-ZnO∕SiOx∕p-Si heterostructured light-emitting diodes have been fabricated using metal-organic chemical-vapor deposition for a comparison study. n-ZnO∕SiOx∕p-Si heterostructures show diodelike rectifying current-voltage characteristic with low breakdown voltage, while n-ZnO∕SiOx∕n-Si heterostructures show symmetric nonlinear current-voltage behavior due to the double Schottky barriers at the interface. Both types of diodes emit light when a positive bias applied at Si side. Ultraviolet emission at ∼390nm with an orange-emission centered at ∼600nm were observed in electroluminescence spectra of n-ZnO∕SiOx∕n-Si diodes, while whitish emission centered at ∼520nm was observed for n-ZnO∕SiOx∕p-Si diodes. The emission mechanisms were discussed.
Bull's eye antennas are capable of efficiently collecting and concentrating optical signals into an ultrasmall area, offering an excellent solution to break the bottleneck between speed and photoresponse in subwavelength photodetectors. Here, we exploit the idea of split bull's eye antenna for a nanometer germanium photodetector operating at a standard communication wavelength of 1310 nm. The nontraditional plasmonic metal aluminum has been implemented in the resonant antenna structure fabricated by standard complementary metal-oxide-semiconductor (CMOS) processing. A significant enhancement in photoresponse could be achieved over the conventional bull's eye scheme due to an increased optical near-field in the active region. Moreover, with this novel antenna design the effective grating area could be significantly reduced without sacrificing device performance. This work paves the way for the future development of low-cost, high-density, and high-speed CMOS-compatible germanium-based optoelectronic devices.
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