Toward Precise n-Type Doping Control in MOVPE-Grown β-Ga2O3 Thin Films by Deep-Learning Approach

In this work, we train a hybrid deep-learning model (fDNN, Forest Deep Neural Network) to predict the doping level measured from the Hall Effect measurement at room temperature and to investigate the doping behavior of Si dopant in both (100) and (010) β-Ga2O3 thin film grown by the metalorganic vapor phase epitaxy (MOVPE). The model reveals that a hidden parameter, the Si supplied per nm (mol/nm), has a dominant influence on the doping process compared with other process parameters. An empirical relation is concluded from this model to estimate the doping level of the grown film with the Si supplied per nm (mol/nm) as the primary variable for both (100) and (010) β-Ga2O3 thin film. The outcome of the work indicates the similarity between the doping behavior of (100) and (010) β-Ga2O3 thin film via MOVPE and the generality of the results to different deposition systems.

Plan-view TEM observation of a single-domain κ-Ga2O3 thin film grown on ε-GaFeO3 substrate using GaCl3 precursor by mist chemical vapor deposition

We demonstrated the growth of a single-domain κ-Ga2O3 thin film on ε-GaFeO3 by using an organic-free compound as a precursor for mist chemical vapor deposition. X-ray diffraction analysis revealed that an 87-nm-thick κ-Ga2O3 thin film was grown almost coherently with slight lattice relaxation. The surface morphology of the κ-Ga2O3 thin film exhibited a step-terrace structure without island growth. Furthermore, plan-view TEM observations revealed that the κ-Ga2O3 thin film grown on ε-GaFeO3 had a single domain, whereas the previously reported κ-Ga2O3 thin film grown on AlN template had a domain structure.

Comparative Study of High-Temperature Annealed and RTA Process β-Ga2O3 Thin Film by Sol–Gel Process

As a wide energy band gap semiconductor, a Ga2O3 thin film was prepared by the sol–gel process with different annealing processes. Since Ga2O3 is a type of metal oxide structure, an oxygen annealing process can be considered to remove oxygen defects. An effective oxygen annealing process can help form a β-Ga2O3 structure with reduced defects. In this study, different types of annealing effects for β-Ga2O3 were investigated and compared. An electric furnace process using thermal effect characteristics of and an Rapid Thermal Annealing (RTA) process applied with an infrared radiation light source were compared. Two and 4 h thermal annealing processes were conducted at 900 °C in the furnace. Meanwhile, to study the optical annealing effects, 2 h furnace at 900 °C + 15 min in rapid thermal annealing and only 15 min in rapid thermal annealing effects were compared, respectively. Through increasing the thermal annealing temperature and time, β-Ga2O3 can be formed even though a sol–gel process was employed in this experiment. An annealing temperature of at least 900 °C was required to form β-Ga2O3 thin film. Moreover, by introducing an RTA process just after the spinning process of thin film, a β-Ga2O3 thin film was formed on the sapphire substrates. Compared with the electric furnace process applied for 2 h, the RTA process performed in 15 min has a relatively short process time and results in similar structural and optical characteristics of a thin film. From the X-ray diffraction patterns and UV spectrometer analysis, optically annealed β-Ga2O3 thin films on the sapphire substrate showed a highly crystalized structure with a wide energy band gap of 4.8 eV.