This thesis focuses on atomic layer deposition (ALD) and its applications in nanotechnology. Two new low-temperature methods for the passivation of GaAs surfaces are presented and the film properties of the plasma ALD grown AlN are studied. A new deposition process for Yb2O3 thin films is developed and utilization of titanium dioxide films for photocatalytic applications is investigated. The photoluminescence intensity of the near surface quantum wells (NSQWs) was used as an indicator for the passivation efficiency. The NSQW structures were coated by AlN or TiN. The AlN layer was deposited using plasma enhanced ALD whereas the TiN film was deposited using thermal ALD. Both coating methods increased the photoluminescence intensity significantly which indicated that the surface recombination rate of GaAs was clearly reduced. The coating layer thickness had a significant effect on the passivation efficiency. The study of the influence of the process parameters on the PEALD AlN film properties revealed that the TMA and NH3 plasma process led to stable film deposition. The growth temperature had the highest effect on the film impurity level: a higher temperature led to a lower hydrogen level. The NH3 plasma pulse time did not have as significant effect on the atomic concentrations. The hydrogen level had an inverse correlation to the AlN film density and refractive index. The developed growth process for the Yb2O3 films was based on the use of ytterbium β-diketonate (Yb(thd)3) and O3 precursors. The optimal growth temperature range was 300-350 °C, where the deposition rate was 0.18-0.20 Å/ cycle. The Yb/O ratio was 0.59 and 0.63 when the growth temperature was 300 and 350 °C, respectively. The impurity levels of H and C were 1.12, 0.65 at.%, in order. The photodegradation of salisylic acid (SA) by TiO2 was investigated. The TiO2 thickness had a clear impact on the SA decomposition rate. A thin 3 nm thick layer did not cause photocatalytic activity. In the range of 3 to 50 nm the photodegradation rate increased and when the film was thicker than 50 nm the decomposition rate stayed relatively constant. The TiO2 deposition temperature showed a clear effect on the the film crystallinity and photodegradation rate. The fastest SA decomposition was observed when the TiO2 growth temperature was 400 °C.
|Publication status||Published - 2018|
|MoE publication type||G5 Doctoral dissertation (article)|
- atomic layer deposition, plasma enhanced atomic layer deposition, GaAs passivation, photocatalyst, AlN, TiN, TiO2