| Summary: | 碩士 === 國立彰化師範大學 === 光電科技研究所 === 102 === There have been a lot of studies on III-V nitride alloys which are well known to be efficiently luminescent semiconductor materials. In particular, III-V compound semiconductor hetero-structures for the ultraviolet light-emitting diodes (UV LEDs) are considered to be the pumping source for producing white-light emission with high color-rendering index. Therefore, enhancing the output power and luminescence efficiency of UV LEDs is one of the important topics at present.
The high threading dislocation (TD) densities in UV LEDs, resulting from the material quality and lattice mismatch, act as non-radiative recombination centers which increase the non-radiative recombination rate and reduce the internal quantum efficiency (IQE). Recently, GaN quantum dots (QDs) have attracted significant attention as promising candidates for structures with high TD density due to the strong carrier localization in QDs, which can minimize the role of dislocation-induced non-radiative recombinations. The main purpose of this thesis is about the investigation on the optoelectronic characterization of UV LEDs with GaN QDs, such as the carrier confinement or emission energy in GaN QD, by using an advanced simulator.
In the chapter 1, the development of solid-state lighting and theoretical description of the wurtzite materials are introduced. The properties of the quantum devices, such as the carrier localization, are also described in detail.
In the chapter 2, the physical parameters and the structure of the UV QDLED used in the APSYS simulator are presented. Some physical mechanisms, for instances, radiative recombination, non-radiative recombination, and calculation of energy bandgaps for III–nitrides are investigated.
In the chapter 3, the influence of AlGaN wetting layers (WLs) in UV QDLEDs are systematically investigated. While the thickness of WLs decreases, the performance of UV QDLEDs decreases due to Auger recombination. However, the efficiencies are limited by the poor electron-hole overlap when the thickness of WLs increases accompanied by large polarization effect.
In the chapter 4, the size-dependent and multiple emissions of UV QDLEDs are investigated numerically. The tunable light emissions in the UV spectral region are obtained by adjusting the size of GaN QDs. The simulation results show that, the UV QDLEDs have stronger carrier confinement and better performance when the height of QDs is within the range from 2.1 nm to 2.3 nm.
Finally, an overall summary of this thesis is given in chapter 5.
|
|---|
