Growths and Characterizations of Wide-Bandgap III-Antimonide and III-Nitride Epilayers and Their Device Structures

• Main Authors: Jehn Ou, 歐震
• Other Authors: Wei-Kuo Chen
• Format: Others
• Language: en_US
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/74590427695931909661

博士 === 國立交通大學 === 電子物理系 === 87 === We have carried out systematic studies on the epitaxial growth of AlAs1-xSbx, GaN and InxGa1-xN compounds using metalorganic vapor phase epitaxy technique. Experimental data indicate that the solid composition of AlAsSb depends strongly on the input reactant flow rates and the growth temperature. A high Sb concentration of AlAsSb alloy can only be obtained at a V/III ratio close to 1, whereas too high the Sb flow rates and too low the V/III ratio will lead to the formation of Sb droplets and Al metal platelets, respectively. For AlAsSb prepared at high growth temperatures, the side reaction of TBAs, b-elimination, is believed to response for the result in a decrease of the As solid concentration. By employing a thermodynamic analysis, a novel phase diagram for AlAsSb with simpler solid-vapor distribution relationship was obtained, according to which the As solid concentration can be directly determined by the input As/Al mole flow rate ratio. The AlAs1-xSbx alloy was also used to fabricate two novel diodes, the enhanced InP Schottky diode and the In0.53Ga0.47As/AlAs0.44Sb0.56/In0.53Ga0.47As single barrier tunneling diode. By introducing AlAsSb into the conventional Schottky structure, the InP Schottky barrier height was improved greatly from 0.45eV to 0.76eV. For single-barrier tunneling diode, a negative differential resistance characteristic was successfully observed at 100 and 300K. A high peak-to-valley current ratio of 4.2 is obtained at 100K, which is the best value ever reported for such type of device. For GaN, the film quality appears to be very sensitive to the buffer layer property and the growth temperature. The optimized buffer layer thickness, temperature ramping rate and growth temperature are found to be around 100~300A, 75~100℃/min, and 1,000~1,050℃, respectively. A phase transition from hexagonal to cubic structure for GaN has been evidenced at a growth temperature around 750℃. The best quality of our GaN films in terms of FWHMs of x-ray and 300K-PL are as narrow as only 160 arcsec and 28meV, respectively. The corresponding electron mobility and carrier concentration also exhibit superior values of 330 cm^2/V and 1.1x10^17 cm^-3, respectively. Regarding to the InGaN growth, our experimental results indicate that the solid composition and characteristic of InGaN are determined not only by the growth temperature, but also by the TMGa and TMIn flow rates. The films with the good structural and optical properties can only be obtained at temperatures above 750℃. For the solid distribution, we found that too high the TMIn flow rate and too low the TMGa flow rate will both bring a decrease of In concentration solid, unfavorable to the high-In content InGaN growth. Besides, the thermodynamic analysis was also performed in our InGaN study. By introducing an empirical high-temperature factor in our modified InGaN growth model, we can successfully predict the solid-vapor distribution in InGaN and the appearance of In-droplets during growth. Based on thermodynamic arguments, the maximum allowed In solid concentration for a single phase InGaN is constrained primarily by the high temperature effect, such as In desorption, and the In saturation vapor pressure. By optimizing the growth conditions, we can obtain high quality InGaN epilayers with the narrow FWHMs of 150 arcsec and 92 meV for (0002) x-ray diffraction and 300K-PL peaks, respectively.