Aluminum nitride (AlN) has versatile and intriguing properties, such as wide direct bandgap, high thermal conductivity, good thermal and chemical stability, and various functionalities. Due to these properties, AlN thin films have been applied in various fields. However, AlN thin films are usually deposited by high temperature processes like chemical vapor deposition. To further enlarge the application of AlN films, atomic layer deposition (ALD) has been studied as a method of AlN thin film deposition at low temperature. In this mini review paper, we summarize the results of recent studies on AlN film grown by thermal and plasma enhanced ALD in terms of processing temperature, precursor type, reactant gas, and plasma source. Thermal ALD can grow AlN thin films at a wafer temperature of 150~550 oC with alkyl/amine or chloride precursors. Due to the low reactivity with NH3 reactant gas, relatively high growth temperature and narrow window are reported. On the other hand, PEALD has an advantage of low temperature process, while crystallinity and defect level in the film are dependent on the plasma source. Lastly, we also introduce examples of application of ALD-grown AlN films in electronics.

The electrical and interfacial properties of HfO2/Al2O3 and Al2O3/HfO2 dielectrics on AlN/p-Ge interface prepared by thermal atomic layer deposition are investigated by capacitance–voltage(C–V) and current–voltage(I–V) measurements. In the C–V measurements, humps related to mid-gap states are observed when the ac frequency is below 100 kHz, revealing lower mid-gap states for the HfO2/Al2O3 sample. Higher frequency dispersion in the inversion region is observed for the Al2O3/HfO2 sample, indicating the presence of slow interface states A higher interface trap density calculated from the high-low frequency method is observed for the Al2O3/HfO2 sample. The parallel conductance method, applied to the accumulation region, shows border traps at 0.3~0.32 eV for the Al2O3/HfO2 sample, which are not observed for the Al2O3/HfO2 sample. I–V measurements show a reduction of leakage current of about three orders of magnitude for the HfO2/Al2O3 sample. Using the Fowler-Nordheim emission, the barrier height is calculated and found to be about 1.08 eV for the HfO2/Al2O3 sample. Based on these results, it is suggested that HfO2/Al2O3 is a better dielectric stack than Al2O3/HfO2 on AlN/p-Ge interface.

An Al2O3/AlN bilayer deposited on GaN by atomic layer deposition (ALD) is employed to prepare Al2O3/AlN/GaN metal-insulator-semiconductor (MIS) diodes, and their interfacial properties are investigated using X-ray photoelectron spectroscopy (XPS) with sputter etch treatment and current-voltage (I-V) measurements. XPS analyses reveal that the native oxides on the GaN surface are reduced significantly during the early ALD stage, indicating that AlN deposition effectively clelans up the GaN surface. In addition, the suppression of Al-OH bonds is observed through the ALD process. This result may be related to the improved device performance because Al-OH bonds act as interface defects. Finally, temperature dependent I-V analyses show that the barrier height increases and the ideality factor decreases with an increase in temperature, which is associated with the barrier inhomogeneity. A Modified Richardson plot produces the Richardson constant of A** as 30.45 Acm−2K−2, which is similar to the theoretical value of 26.4 Acm−2K−2 for n-GaN. This indicates that the barrier inhomogeneity appropriately explains the forward current transport across the Au/Al2O3/AlN/GaN interface.

We performed temperature dependent current-voltage (I-V) measurements to characterize the electrical properties of Au/Al2O3/n-Ge metal-insulator-semiconductor (MIS) diodes prepared with and without H2O prepulse treatment by atomic layer deposition (ALD). By considering the thickness of the Al2O3 interlayer, the barrier height for the treated sample was found to be 0.61 eV, similar to those of Au/n-Ge Schottky diodes. The thermionic emission (TE) model with barrier inhomogeneity explained the final state of the treated sample well. Compared to the untreated sample, the treated sample was found to have improved diode characteristics for both forward and reverse bias conditions. These results were associated with the reduction of charge trapping and interface states near the Ge/Al2O3 interface.

Using current-voltage (I-V) and capacitance-voltage (C-V) measurements, the electrical properties of Au and Cu Schottky contacts to n-Ge were comparatively investigated. Lower values of barrier height, ideality factor and series resistance were obtained for the Au contact as compared to the Cu contact. The values of capacitance showed strong dependence on the bias voltage and the frequency. The presence of an inversion layer at the interface might reduce the intercept voltage at the voltage axis, lowering the barrier height for C-V measurements, especially at lower frequencies. In addition, a higher interface state density was observed for the Au contact. The generation of sputter deposition-induced defects might occur more severely for the Au contact; these defects affected both the I-V and C-V characteristics.

The electrical properties of Au/n-type Ge Schottky contacts with different contact areas were investigated using current-voltage (I-V) measurements. Analyses of the reverse bias current characteristics showed that the Poole-Frenkel effect became strong with decreasing contact area. The contribution of the perimeter current density to the total current density was found to increase with increasing reverse bias voltage. Fitting of the forward bias I-V characteristics by considering various transport models revealed that the tunneling current is dominant in the low forward bias region. The contributions of both the thermionic emission (TE) and the generation-recombination (GR) currents to the total current were similar regardless of the contact area, indicating that these currents mainly flow through the bulk region. In contrast, the contribution of the tunneling current to the total current increased with decreasing contact area. The largest E00 value (related to tunneling probability) for the smallest contact area was associated with higher tunneling effect.