Abstract
We formed a p–n homojunction by implanting nitrogen ions, serving as a p-type dopant, into an n-type ZnO crystal. A forward bias current was injected into the crystal while irradiating it with light, bringing about Joule heating which annealed the crystal and changed the spatial distribution of the N-dopant concentration. This activated the N-dopant, causing its concentration distribution to be modified in a self-organized manner so as to be suitable for generating dressed photons. A light-emitting diode fabricated by this dressed-photon assisted annealing method showed electroluminescence at room temperature. In a device fabricated by annealing under irradiation with 407 nm-wavelength light, at a forward bias current of 20 mA, the peak wavelength of the electroluminescence was 436 nm, the optical output power was 6.2 μW, and the external quantum efficiency was 1.1×10−4. The emission spectral profile depended on transitions from intermediate phonon states.
Highlights
ZnO is a direct-transition, wide bandgap semiconductor and is expected to be used as a material for fabricating optical devices such as UV light-emitting diodes and laser diodes [1].T
When Joule heating is generated by the forward bias current, the N dopant in the p–n junction is diffused; at regions where dressed photons are generated by the process described above, stimulated emission occurs, driven by the dressed photons
The surface temperature rose to 100 ◦C when annealing commenced, and dropped, reaching a constant temperature of 74 ◦C after about 60 minutes. This temperature drop was caused by the generation of dressed photons as annealing progressed, bringing about stimulated emission, and by part of the electrical energy added to produce Joule heating being dissipated in the form of optical energy
Summary
ZnO is a direct-transition, wide bandgap semiconductor and is expected to be used as a material for fabricating optical devices such as UV light-emitting diodes and laser diodes [1]. On the other hand, according to recent research by the authors, the possibility of fabricating p-type ZnO has been increased by employing annealing using dressed photons [15], a technique known as dressed-photon assisted annealing. This annealing method has already been applied to Si, an indirect-transition semiconductor, to realize high-efficiency p–n homojunction-structured LEDs using bulk Si crystal [16]. We successfully fabricated a p–n homojunction-structured LED that emits at room temperature by applying dressed-photon assisted annealing to a bulk ZnO crystal. The principle of the annealing technique, the device fabrication method, and the characteristics of the fabricated devices are described in the following
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