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

AlGaN based emitting devices have been attracting considerable attention because ofits significant application in the ultraviolet field such as white light illumination, air andwater purification, sterilization, high-density storage. The common substrate for growingAlGaN materials is sapphire. The quantum efficiency of AlGaN based emitting devices issignificantly affected by the high density of dislocation like1010-1012cm-2in materialsgrowing on sapphire substrates. After years of exploration, one of the recognized solutionsis growing high quality AlN templates for AlGaN devices on sapphire substrates. ThickAlGaN films without crack can be obtained on these AlN templates. Growing high qualityAlN 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 increasethe quantum efficiency due to its specific performance. The scale of quantum dots isrelated to Bohr radius of the electron, the movement of electrons is confined in quantumdots, and the recombination prlbility of carrier increases. The investigation of growingquantum dots is valuable in both basic physics research and device applications (includelasers, single optical sources, quantum calculation).The first part of this dissertation describes the investigation of AlN templates viametalorganic chemical vapor deposition (MOCVD) in detail. A combined growthtechnical, a low temperature nucleation layer and pulsed atom layer epitaxy (PALE), hasbeen applied for growing AlN materials firstly. The effects of growth conditions on thequality of AlN films and also AlN growth mode are investigated to solve the problems ingrowing AlN films. The effects of pretreatment of sapphire substrates, low temperaturenucleation layer growth conditions (include growth temperature, layer thickness, V/III),and PALE growth conditions (include growth temperature, V/III, and growth rate) on AlNfilms are mainly studied. With different pretreatment conditions, different strain relaxationmechanisms induced by the lattice mismatch of AlN and sapphire are observed. Thenitridation 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 halfmaximum (FWHM) of52arcsec and (102) FWHM of1106arcsec are obtained. Thesamples 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 quantumdots. The growth of GaN quantum dots on AlN templates is investigated firstly. Thegrowth methods of GaN quantum dots include S-K (Stranski-Krastanov) growth mode andGa droplets epitaxy. The effects of the growth condition such as growth time, flux, reactorpressure, and growth temperature on the morphology of GaN quantum dots areinvestigated in S-K growth mode. GaN quantum dots are not achieved during ourexperiments due to the high growth rate. However, the results show that GaN quantumdots could be realized by S-K growth mode if the growth thickness of GaN quantum dotscould be controlled. During the experiments of Ga droplets epitaxy, the effects of eachgrowth process on the GaN quantum dots are investigated. Based on the experiments, thesize, 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 adensity varied between108cm-2and1010cm-2. An emission peak at310nm is observed inPL spectrum. Then, the growth conditions of caplayer are investigated on Ga dropletsepitaxy quantum dots. Samples with flat AlN caplayer are obtained under optimalconditions. GaN quantum dots are also grown on P-GaN templates through Ga dropletsepitaxy. The effects of growth conditions on the morphology of GaN quantum dots areinvestigated.At last, the growth of InGaN quantum dots on GaN templates is investigated via S-Kgrowth mode. The size and density of InGaN quantum dots are controlled by the growthconditions such as growth temperature, growth rate, and In content. InGaN quantum dotswith20-80nm wide,2-15nm high, and density of1010cm-2are obtained.