Study On The Growth And Optical Properites Of Low-dimensional InGaN/GaN Quantum Well Structures

The commercialization of GaN based semiconductor devices gives a boost to the rapid development in Ⅲ-Nitrides research field. Since Ⅲ-nitride (GaN-based) semiconductors have excellent physical and chemical stability, besides, the band gap can be consisitently tuned from0.7eV to6.2eV and cover the extensive spectrum range between near-infrared to ultraviolet, they have been developed as the favorite materials for optoelectronic device applications. Nowadays, abundant and branchy research aspects of Ⅲ-nitrides are developing, and the development of GaN-based LED research have also reached unprecedented level. Traditional materials and device structure is difficult to meet the requirement of commercialization. As a result, the development of GaN-based LEDs is steping to the tendency of low dimension and non-polarization. Novel low-dimensional structure and lower polarization effect will bring GaN-based optoelectronic devices more excellent physical properties and great potential applications.This dissertation mainly discusses the core low-dimensional InGaN/GaN quantum well structure of LEDs. Our work systematically explores the growth role of InGaN quantum dots (QDs) formation in the process of InGaN/GaN single quantum well growth, obtaining the growth temperature window and properties for the formation of InGaN QDs. Also we have carried out the research of semipolar InGaN/GaN multiple quantum wells (MQWs). As the conventional semipolar and nonpolar GaN planar substrates are costly, small in size, lack of proper template, and with poor crystal quality, we apply the selective area epitaxy to grow semipolar InGaN/GaN MQWs. This technology could reduce the quantum well threading dislocation density effectively, and obtain hybrid luminescence from semipolar and polar MQWs. According to the mechanism that Si atom can be used as antisurfactant for the formation of InGaN QDs, we have systematically analyzed the InGaN QD properties grown by SiO2prtreated method. And using the InGaN QDs as growth template, hybrid structure of quantum well and QDs with high light output efficiency has been realized by stress transfer effect. The main content and results are listed as follow:1. By changing the InGaN growth temperature and PL measurement, it is obvious that InGaN under700℃shows two-dimensional InGaN/GaN quantum well growth behavior. InGaN growth temperature below700℃forms InGaN QD structure, because the atom migration ability has reduced under low temperature. Experiments reveal that ultra-low temperature would degrade the InGaN QD quality and luminescence property, forming QW and QD hybrid structure. These results show InGaN QDs grown under690℃have the highes luminescence efficiency.2. Slective area epitaxy has been applied to grow GaN semipolar GaN stripe templates. Stripes oriented along the direction of [1120] form smooth triangular {1101} semipolar plane, and the morphology is independent of reactor pressure and growth temperature. While stripes in the [1100] direction are sensitive to the reactor pressure and growth temperature, and the morphology are composed of (0001),{1122} and{1120} plane. It is suggested that these morphological changes are strongly related to the surface energy and stability.3. InGaN/GaN MQWs are grown on different GaN semopolar planes. Uniform emission at400nm has been obtained for triangular MQWs oriented the direction of [1120]. The MQWs grown along [1100] direction is composed of c plane and {1122} plane, and shows dual-color emission peaks. Local CL spectra demonstrate that the emission peak at390nm originates from inclined semipolar MQWs, while the420nm peak is attributed to the MQWs on c plane. MQWs on semipolar plane show uniform luminescence property, because the dislocation and defect density are significantly reduced. The redshift in emission wavelength for (0001) plane InGaN/GaN MQWs of selectively grown trapezoid aling the [1100] direction compared to its inclined{1122} plane MQWs is attributed to the indium enrichment in the central c plane MQWs, the indium enrichment originates from additional source supply due to the surface migration effect and lateral vapor-phase diffusion. Another reason is due to the reduction of quantum confined stark effect of MQWs on semipolar plane compared to MQWs on c plane. Strain-induced polarization model has been used to calculate the piezoelectric polarization and total polarization of InGaN/GaN MQWs on GaN c plane and semipolar plane. It has been proved that the polarization effect of MQWs on semipolar plane is weaker than that on c plane all the time, resulting in the reduced quantum confined stark effect of MQWs on semipolar plane. The thickness of InGaN QW layer on semipolar plane is thinner than that of c plane, inducing the blue shift of semipolar MQWs.4. The novel SiO2pretreated method has been demonstrated to grow InGaN quantum dots (QDs). By controlling the InGaN growth time, different size InGaN QDs with high quality have been obtained. The strong PL from the uncapped QDs at room temperature indicates higher carrier recombination efficiency of QDs than traditional thin film. Two periods of InGaN/GaN structure has been grown on the surface of InGaN QDs which were grown by SiO2pretreated method. InGaN multiple-layer stacked QDs are obtained due to the stress transfer effect. Dual-color emission is observed by PL measurement. The low-energy peak with wide linewidth originates from QD localization state emission, and shows a significant blueshift and a linewidth broadening as the increase of PL excitation power. The high-energy peak is attributed to the quantized state transition. A slight blueshift and linewidth narrowing has occurred for the high-energy peak which is consistent with the quantum well emission. The results display different optical properties between InGaN QDs and QW transition.