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In this paper, for the first time, the switchable two-color quantum dot laser has been realized considering solution process technology, which has both simultaneous and lonely lasing capability exploiting selective energy contacts. furthermore, both channels can be modulated independently, which is a significant feature in high-speed data transmission. To this end, utilizing superimposed quantum dots with various radii in the active layer provides the different emission wavelengths. In order to achieve the different sizes of QDs, solution process technology has been used as a costeffectiveness and fabrication ease method. Moreover, at the introduced structure to accomplish the idea, the quantum wells are used as separate selective energy contacts to control the lasing channels at the desired wavelength. It makes the prominent device have simultaneous lasing at different emission wavelengths or be able to lase just at one wavelength. the performance of the proposed device has been modeled based on developed rate equation by assuming inhomogeneous broadening of energy levels as a consequence of the size distribution of quantum dots and considering tunnel injection of carriers into the quantum dots via selective energy contacts. Based on simulation results, the simultaneous lasing in both or at one of two wavelengths 1.31 μm and 1.55 μm has been realized by the superimposition of two different sizes of InGaAs quantum dots in a single cavity and accomplishment of selective energy contacts. Besides, controlling the quantum dot coverage leads to managing the output power and modulation response at the desired wavelengths. By offering this idea, one more step is actually taken to approach the switchable QD-laser by the simple solution process method.Nowadays, multi-wavelength lasers have been committed to numerous applications in the field of imaging, tomography and ultra-fast data communication. Thus, the ability to achieve simultaneous lasing at different wavelengths has been the subject of enormous research in the past few years 1-5 . In addition, lasers have drawn great attention due to their wide potential applications in all-optical switching system 6 and on/off switching behavior 7 , ultrafast photonics 8-10 , playing roles as the light irradiation source for cancer therapy 11-14 , analyzing the photo-thermal properties 15-17 and excitation source for Raman spectra measurement 18,19 . Moreover, the high performance of lasers can be accomplished by utilizing quantum dots (QDs) in the active region of laser diodes. Hence, the quantum dot lasers (QD-Lasers) have been received great attention in recent decades among different types of laser structures [20][21][22][23][24][25] . The low threshold current, high modulation bandwidth, narrow linewidth, low-frequency chirp, and temperature stability are the superior advantages of QD-lasers due to the QDs' unique properties such as quantum confinement effect and delta-function-like density of states 4,26-29 . Consequently, the realization of switchable multi-wavelength las...

In this research paper, fabrication of novel CdSe\ZnS QD-LEDs with solution processing method is presented and the impact of trap energy levels in the electron and hole transport levels on these QD-LEDs brightness is investigated. Two types of QD-LEDs are fabricated with ITO as the transparent anode electrode, NiO nanoparticles as the hole transport layer (HTL), CdSe\ZnS QDs as the luminescent layer, ZnO: Ga as the electron transport layer (ETL), and Al as the cathode electrode. The NiO nanoparticles are synthesized by solgel or alternatively electrochemical method. Formation of different trap levels is observed in the crystal structures of the NiO nanoparticles synthesized by each of these methods. Considering the electrochemically prepared NiO nanoparticles, it is found that the density of trap levels is higher in the crystal structure of the NiO nanoparticles synthesized by sol-gel method and the device fabricated by the later material shows higher performance. Calculation of the electronic structure of ZnO: Ga by DFT methods (GGA-PBE) indicates that doping of Ga in the structure of crystalline ZnO creates new energy levels in conduction band and intermediate bands at the band gap of ZnO host. It facilitates electron injection from Al cathode to the ZnO:Ga ETL layer and from this layer to the QD luminescent layer. The fabricated devices show turn-on lower voltages than 5V in which a peak brightness of 500cdm -2 and 340cd m -2 is measured for the LEDs fabricated with sol-gel and electrochemically synthesized NiO nanoparticles respectively.Index Terms-Light emitting diode, Quantum dot, NiO, ZnO: Ga, Photo luminescence 1536-125X (c)

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