Nanowire/Nanobelt Based Hybrid Light Emitting Diodes

High performance light emitting diodes with higher external quantum efficiency (EQE), lower cost, longer lifetime and more tunable emitting wavelength are always a global pursue. Although enormous interests and efforts have been attracted into this field and great improvements and accomplishments have been made, there still exist lots of aspects of today’s lighting source need to be improved for various requirements. These years, nanowire-based LED has aroused lots of research interests for its advantages such as high emission extraction efficiency compared with traditional film based LEDs, accurate control of doping and easy large scale production. Furthermore, photons and electrons confined at nanoscale have demonstrated exceptional and exciting behaviors that have not been observed in macroscopic scale such as the polariton emission originate from strong interaction between photons and phonons, surface plasmon enhanced spontaneous emission. Especially, LEDs with dimension at nanoscale have great potential in the new generation of high speed optical communication devices and are indispensable in highly-integrated optical chips. Therefore, in this thesis, we focus our efforts into fabricating novel nanowire-based LEDs and also make incisive analysis about the carrier transportation and radiative recombination along with other interesting factors that have influences on the performance of the LED.In the first part, we are dedicated into clarifying the importance and significance of building nanowire-based LEDs from the aspects of its advantages and potential applications. We also make a clear research goal that we will demonstrate an Ag nanowire based high efficiency Schottky junction ultraviolet LED with low cost and also a multi-color LED based on CdS nanobelt/GaN p-n junction contact.In the second part, a thorough description of the procedures involved in the nanowire growth is made and details of the equipment used and parameter for successful fabrication is provided. There are mainly two types of nanowires mentioned in this part, the first one is In-doped CdS nanowire and nanobelt based on VLS growth and another one is Ag nanowire fabricated based on a soft, self-seeding process.In the third part, we mainly focus on the high performance LED based on Ag nanowire/p-GaN Schottky junction contact. We firstly elaborate the details in why we choose this structure to realize efficient LED and how this structure is built. Then, we performed both electrical and optical properties measurements including current-voltage testing, spectrum testing and external quantum efficiency calculation. These experimental results justify the high performance of our device. Theoretical analysis are also made based on extinction cross section calculation and the temperature distribution simulation. These analysis along with the experiments help give a comprehensive understanding in achieving high performance Schottky type LEDs.In the fourth part, we firstly demonstrate a multi-color LED based on CdS nanobelt/p-GaN p-n junction contact. This device shows excellent rectification properties and can realize strong emission from CdS and GaN simultaneously. In the experiments, we firstly reported an interesting phenomenon that the radiative recombination rate of GaN increases at faster rate than that of CdS. Further analysis justifies that this result is a combined effects of modulations of carrier transportation due to both energy band alignment and the magnitude of electric field within the junction of the device. In the last, we also explore enhancing the EQE of this novel semiconductor nanobelt based LED using piezo-phototronic effects which is a coupling of electrons, photons and phonons. These analyses demonstrate that the piezo-charges located at the interface of CdS nanobelt and GaN film contributes to the realignment of the energy band and combination of carriers which can enhance the radiative recombination.In the fifth part, we make a conclusion of the main accomplishments in this thesis and also propose several valuable areas that prospective work can be performed.