In-situ deposition of high-k dielectrics on III-V compound semiconductor in MOCVD system

[摘要] In situ deposition of high-k materials to passivate the GaAs in metal organic chemical vapor deposition (MOCVD) system was well demonstrated. Both atomic layer deposition (ALD) and chemical vapor deposition (CVD) methods were applied in this research. The CVD aluminum nitride (AIN) was first selected to be in situ deposited on GaAs surface by using trimethlyaluminum(TMA) and dimethylhydrazine (DMHy). However, the frequency dispersion of Capacitance-Voltage (C-V) curves for in situ AIN/GaAs samples are always large because of the existence of high interfacial defect state density (Dit) due to the nitridization of the GaAs surface during the AIN deposition. In order to avoid the surface reaction, in situ ALD of aluminum oxide (A1₂O₃) on GaAs in MOCVD system was proposed. Isopropanol (IPA) was chosen as the oxygen source for A1₂O₃ ALD and the mechanism was investigated. Pure A120 3 thin film was obtained and no arsenic or gallium oxide was observed at the interface. Both frequency dispersion of C-V curve and the Di, of oxide/p-GaAs interface are low for this process. In situ CVD A1₂O₃ on GaAs was also performed. Gallium oxide (Ga₂O₃) was observed at the interface. The Ga₂O₃ was enriched in the A1₂O₃ above the interface during the deposition process and a possible mechanism was proposed. This layer reduces the frequency dispersion of the C-V characteristics and lowers the Dit of n-type GaAs sample. After the in situ method had been successfully established, ex situ experiments was also performed to compare the results with in situ process in the same MOCVD system. Annealing native oxide covered GaAs samples in Arsine (AsH 3) prior to ALD A1₂O₃ results in C-V characteristics of the treated samples that resemble the superior C-V characteristics of p-type GaAs. Besides, both TMA and IPA show self-cleaning effect on removing the native oxide in ex situ process. The discrepancy in the C-V characteristics was observed in in situ p- and n-type GaAs samples. Finally, the entire Dit energy distributions of interfaces from different processes were determined by conductance frequency method with temperature-variation C-V measurement. The existence of Ga₂O₃ at interface was found to be the possible source to lower the density of mid-gap defect state. From the C-V simulation, the mid-gap defect states are acceptor-like (Gallium Vacancies) and the source to cause high frequency dispersion of the C-V curves for n-type substrate. The relation between the interfacial defect state distribution and the processes was correlated.

[发布机构] Massachusetts Institute of Technology