| Summary: | 博士 === 國立交通大學 === 電子物理系所 === 102 === For III-nitride growth, the metal alkyls are generally used as source precursors for group III elements while ammonia (NH3) is used as the source precursor of nitrogen. Growth and parasitic reactions of nitride semiconductor can be characterized into two reaction pathways, adduct reaction and radical reaction pathway. Adduct reaction start from TMIII:NH3 and followed by a CH4 elimination, while radical reaction through precursors decomposition individually. Each pathway is responsible for producing a group of chemical species that may eventually dissociate to participate the epitaxial growth or associate to become parasitic reaction. In this dissertation, GaN epitaxial layer has been grown by conventional MOVPE and two-heater MOVPE with ceiling temperature fixed at 1050℃. Experimental results indicate that there exhibits an activation of 3.7 kcal/mol at mass transport region for both growth methods, which is agreed with the value in MOMBE GaN growth. It is known the MBE growth is governed by surface kinetics, the similarity in value of activation energy seems to imply the MOVPE GaN growth is also controlled by surface kinetics, suggesting the radical pathway dominate the growth. Based on the results of GaN growth mechanism, we further extended our study toInGaN growth. We tentatively grew InGaN film at 600℃ in mass transport region to avoid the presence of high temperature effects and with ceiling temperature varied from 600 to 950℃, which could enhance parasitic reactions, if any, in the gas phase. We indeed find parasitic reactions take place in the hot temperature zone above the substrate. The calculated activation energy is 31.4 kcal/mol. Such a low value in activation energy implies that InN parasitic reaction is dominant by adduct pathway. Normally, the presence of parasitic reactions could result in a non-linear growth rate along the flow direction. Nevertheless, we do not find such event occurred. For instance, the sample of x=0.40 InGaN film grown at the substrate temperature of 650℃ and ceiling temperature of 900℃ appears to have mean PL (at 18K) peak wavelength and FWHM are 808±6nm and 229±18meV, respectively. Finally, growth mechanism of InN nanodots by conventional MOVPE was also investigated. It is found that the dot growth at 650oC follows well with standard nucleation theory and the dot density can be express by N∝(R/D0)p exp(E*/kT), where p =i/(i+2) and i is the critical cluster size, which is found to be 8 for InN dot growth. Moreover, there appears sharp transition at V/III=12000 in terms of dot density and morphological size which we ascribe it to the change of diffusivity of decisive adatoms from N adatoms under In-rich conditions to In adatoms under N-rich conditions.
|
|---|
