| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Thursday Sessions |
| Session EM+NS-ThA |
| Session: | Wide and Ultra-wide Band Gap Materials for Electronic Devices: Growth, Modeling, and Properties |
| Presenter: | Ramón Collazo, North Carolina State University |
| Authors: | R. Collazo, North Carolina State University S. Washiyama, North Carolina State University I. Bryan, North Carolina State University P. Reddy, Adroit Materials Inc. S. Mita, Adroit Materials Inc. Z. Sitar, North Carolina State University |
| Correspondent: | Click to Email |
AlGaN have been considered to be essential for the development of optoelectronic and electronic devices such as deep UV LEDs and other power devices. However, even under well-controlled growth conditions it is difficult to precisely predict the behavior of AlGaN growth with regards to Al-concentration and related defect incorporation. We have developed a thermodynamic model for the calculation of the Ga supersaturation during the growth of GaN by metalorganic chemical vapor deposition (MOCVD), which was successfully used to predict incorporation of impurities such as carbon as well as the surface morphology (Mita et al., JAP 104, 13521). This model was extended to evaluate the supersaturation of Al and Ga in AlGaN growth and to allow for the prediction of the properties of MOCVD grown AlGaN layers. Non-linear equations for Al and Ga equilibrium vapor pressure calculation describe the process under the following assumptions: (1) under low total pressure, gas phase reactions between the metalorganics and NH3 are negligible; the III metal precursors are irreversibly cracked on the growth surface, thus, Al, Ga, NH3, H2 and N2 are analyzed; (2) number of moles of growing species are conserved; (3) at least some NH3 molecules are thermally cracked in the gas phase. Using the resulting model, the influence of growth parameters such as V/III and flow rate on AlGaN growth was determined through the dependence of the Ga and Al supersaturation. The independent parameters for the calculations included the growth conditions that were set by typical conditions for AlGaN MOCVD growth. Calculation showed a significantly lower equilibrium vapor pressure for Al (10-12-10-16 Torr) than for Ga (10-4-10-6 Torr). The Ga equilibrium pressure monotonously decreased with increasing V/III ratio, while NH3 thermal cracking was more significant on the equilibrium pressure, as expected from Le Chatelier`s principle. The significant difference in the supersaturation between Ga and Al has a significant influence on the growth of ternary AlGaN compounds and need to be considered for finding appropriate and robust growth conditions at high temperatures, exceeding 1150 ºC. A processing AlGaN compositional phase diagram dependent on the typical growth conditions will be presented. In addition, experimental validation of this model with respect to Al composition, process stability and robustness will be discussed. This validation will be presented in terms of temperature and V/III ratio.