Abstract:We investigate excitonic carrier diffusion in both bulk ZnO and nanorods (NRs). Using time-resolved differential reflectivity spectroscopy, we observe a fast decaying component together with a longer exponential relaxation. In bulk ZnO, we find that the fast decay term (∼1 ps) originates from excitonic diffusion along the growth direction. By probing at both the A and B excitons, we find different diffusion coefficients for each. In ZnO nanorods, the diffusion contribution is missing. We attribute this to two … Show more
“…This number is much smaller than the Mott density of 10 17 cm −3 or so in ZnO 65 , which further suggests that the present lasing is excitonic-like rather than electron-hole plasma type. The resulting excitons, formed by the interaction of these hole carriers and abundant electrons flowing in the devices, paves the way to excitonic emission 66 .Figure 5Simulation of hole generation and mode behavior in MgZnO MSM devices. Band diagram of MgZnO along A-A′ section direction for ( a ) V = 0 V and ( b ) V = 25 V. CBM and VBM in ( a ) stands for conduction band minimum and valance band maximum, respectively.…”
Semiconductor lasers in the deep ultraviolet (UV) range have numerous potential applications ranging from water purification and medical diagnosis to high-density data storage and flexible displays. Nevertheless, very little success was achieved in the realization of electrically driven deep UV semiconductor lasers to date. In this paper, we report the fabrication and characterization of deep UV MgZnO semiconductor lasers. These lasers are operated with continuous current mode at room temperature and the shortest wavelength reaches 284 nm. The wide bandgap MgZnO thin films with various Mg mole fractions were grown on c-sapphire substrate using radio-frequency plasma assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) random laser devices were fabricated using lithography and metallization processes. Besides the demonstration of scalable emission wavelength, very low threshold current densities of 29~33 A/cm2 are achieved. Numerical modeling reveals that impact ionization process is responsible for the generation of hole carriers in the MgZnO MSM devices. The interaction of electrons and holes leads to radiative excitonic recombination and subsequent coherent random lasing.
“…This number is much smaller than the Mott density of 10 17 cm −3 or so in ZnO 65 , which further suggests that the present lasing is excitonic-like rather than electron-hole plasma type. The resulting excitons, formed by the interaction of these hole carriers and abundant electrons flowing in the devices, paves the way to excitonic emission 66 .Figure 5Simulation of hole generation and mode behavior in MgZnO MSM devices. Band diagram of MgZnO along A-A′ section direction for ( a ) V = 0 V and ( b ) V = 25 V. CBM and VBM in ( a ) stands for conduction band minimum and valance band maximum, respectively.…”
Semiconductor lasers in the deep ultraviolet (UV) range have numerous potential applications ranging from water purification and medical diagnosis to high-density data storage and flexible displays. Nevertheless, very little success was achieved in the realization of electrically driven deep UV semiconductor lasers to date. In this paper, we report the fabrication and characterization of deep UV MgZnO semiconductor lasers. These lasers are operated with continuous current mode at room temperature and the shortest wavelength reaches 284 nm. The wide bandgap MgZnO thin films with various Mg mole fractions were grown on c-sapphire substrate using radio-frequency plasma assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) random laser devices were fabricated using lithography and metallization processes. Besides the demonstration of scalable emission wavelength, very low threshold current densities of 29~33 A/cm2 are achieved. Numerical modeling reveals that impact ionization process is responsible for the generation of hole carriers in the MgZnO MSM devices. The interaction of electrons and holes leads to radiative excitonic recombination and subsequent coherent random lasing.
“…27 These holes readily interact with electrons in the conduction band to form excitons and emit light through excitonic EL. 28 Due to the limited hole injection, the exciton recombination process is believed to be responsible for the lasing behavior since population inversion is not necessary in excitonic lasing generation. 29 The light is mostly generated in the nanowires below the Au/ZnO interface because of the small hole diffusion length.…”
Electrically pumped random lasing based on an Au-ZnO nanowire Schottky junction diode is demonstrated. The device exhibits typical Schottky diode current-voltage characteristics with a turn-on voltage of 0.7 V. Electroluminescence characterization shows good random lasing behavior and the output power is about 67 nW at a drive current of 100 mA. Excitonic recombination is responsible for lasing generation.Zn plasma is only observed under high applied bias, which can be distinguished from the random lasing spectral features near 380 nm. The laser diode based on the Schottky junction provides an alternative approach towards semiconductor random lasers.
“…Since the electrons and holes are flowing in the opposite direction, there are ample probabilities for them to couple with each other and form excitons. [27,28] These excitons then recombine to emit light almost instantaneously. [28] It should be noted that this device is different with the metal-insulator-semiconductor laser device, where a large barrier at the metal-semiconductor interface is used to confine electrons in the semiconductor for lasing as reported in Ref.…”
Au/ZnO microwire Schottky diodes are fabricated. The devices exhibit typical Schottky diode I–V behavior with a turn‐on voltage of about 0.72 V. The hexagonal ZnO microwires act as whispering gallery mode (WGM) lasing microcavities. Under forward bias, a three‐microwire device exhibits WGM ultraviolet lasing spectra with a quality factor of about 1287. Output power of the laser has been measured at various injection currents, indicating threshold behavior with a threshold current of about 59 mA. Due to limited hole injection in the operation of Schottky diode, the lasing is a result of an excitonic recombination within the WGM cavity.
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