Investigation Of The MOCVD Growth Of AIN Films,GaN Quantum Dots And InGaN Quantum Dots On Sapphier Substrates

AlGaN based emitting devices have been attracting considerable attention because of its significant application in the ultraviolet field such as white light illumination, air and water purification, sterilization, high-density storage. The common substrate for growing AlGaN materials is sapphire. The quantum efficiency of AlGaN based emitting devices is significantly affected by the high density of dislocation like1010-1012cm-2in materials growing on sapphire substrates. After years of exploration, one of the recognized solutions is growing high quality AlN templates for AlGaN devices on sapphire substrates. Thick AlGaN films without crack can be obtained on these AlN templates. Growing high quality AlN templates on sapphire substrates has been a key step for AlGaN devices. In nowadays, researchers are inserting quantum dots into the active layer of AlGaN devices to increase the quantum efficiency due to its specific performance. The scale of quantum dots is related to Bohr radius of the electron, the movement of electrons is confined in quantum dots, and the recombination prlbility of carrier increases. The investigation of growing quantum dots is valuable in both basic physics research and device applications (include lasers, single optical sources, quantum calculation).The first part of this dissertation describes the investigation of AlN templates via metalorganic chemical vapor deposition (MOCVD) in detail. A combined growth technical, a low temperature nucleation layer and pulsed atom layer epitaxy (PALE), has been applied for growing AlN materials firstly. The effects of growth conditions on the quality of AlN films and also AlN growth mode are investigated to solve the problems in growing AlN films. The effects of pretreatment of sapphire substrates, low temperature nucleation layer growth conditions (include growth temperature, layer thickness, Ⅴ/Ⅲ), and PALE growth conditions (include growth temperature, V/III, and growth rate) on AlN films are mainly studied. With different pretreatment conditions, different strain relaxation mechanisms induced by the lattice mismatch of AlN and sapphire are observed. The nitridation pretreatment eliminates the misoriented crystals and the resulted AlN is Al-face. By optimizing the growth conditions of AlN films, samples with (002) full width of half maximum (FWHM) of52arcsec and (102) FWHM of1106arcsec are obtained. The samples are coalescence completely without any pits. Based on the nucleation layer, a 636nm thick AlN layer without cracks is obtained through PALE growth technical.The second part of this dissertation describes the investigation of growing quantum dots. The growth of GaN quantum dots on AlN templates is investigated firstly. The growth methods of GaN quantum dots include S-K (Stranski-Krastanov) growth mode and Ga droplets epitaxy. The effects of the growth condition such as growth time, flux, reactor pressure, and growth temperature on the morphology of GaN quantum dots are investigated in S-K growth mode. GaN quantum dots are not achieved during our experiments due to the high growth rate. However, the results show that GaN quantum dots could be realized by S-K growth mode if the growth thickness of GaN quantum dots could be controlled. During the experiments of Ga droplets epitaxy, the effects of each growth process on the GaN quantum dots are investigated. Based on the experiments, the size, density, and quality of GaN quantum dots are controlled by the growth conditions. The horizontal and vertical size of quantum dots are less than100nm and10nm with a density varied between108cm-2and1010cm-2. An emission peak at310nm is observed in PL spectrum. Then, the growth conditions of caplayer are investigated on Ga droplets epitaxy quantum dots. Samples with flat AlN caplayer are obtained under optimal conditions. GaN quantum dots are also grown on P-GaN templates through Ga droplets epitaxy. The effects of growth conditions on the morphology of GaN quantum dots are investigated.At last, the growth of InGaN quantum dots on GaN templates is investigated via S-K growth mode. The size and density of InGaN quantum dots are controlled by the growth conditions such as growth temperature, growth rate, and In content. InGaN quantum dots with20-80nm wide,2-15nm high, and density of10cm-2are obtained.