The data provided here has been used in the preperation of figures for the following manuscript:

T. Partida­Manzanera,  J.W. Roberts, T.N. Bhat, Z. Zhang, H.R. Tan, S.B. Dolmanan, N. Sedghi, S. Tripathy, and R.J. Potter, 'Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)x(Al2O3)1­x dielectrics for GaN/AlxGa1­xN/GaN high electron mobility transistors applications', submitted to Journal of Applied Physics (2015). 


Experimental procedure


AlxGa1­xN/GaN HEMT structures were grown on a 1.0 mm thick 200 mm diameter Si(111) substrate (supplied by MRS, prime grade) using an AIXTRON CCS metal organic chemical vapor deposition (MOCVD) system. The total thickness of the nitride stack is about 4.3 µm. It includes a ~400 nm thick AlN nucleation layer, three step­graded AlxGa1­xN intermediate layers with a total thickness of approximately 1.8 µm, a ~1.8 µm carbon­doped GaN buffer layer and a ~300 nm undoped GaN channel. The top HEMT structure consists of a thin AlN spacer, a ~18­19 nm Al0.24Ga0.76N barrier layer and a ~4.0 nm top undoped thin GaN cap. Prior to ALD, the HEMT samples were treated with an ex­situ wet­chemical cleaning process. The samples were sonicated in separate acetone and isopropanol (supplied by Sigma­Aldrich®, 99.5% purity) for 10 min each to remove organic contaminants and then rinsed in DI water for 2 min and dried with compressed nitrogen.

Ta­doped Al2O3 films were deposited at 250ºC using an Oxford Instruments OpAL thermal ALD reactor. Electronic grade trimethylaluminium (TMA) and pentakis(dimethylamino)tantalum (PDMAT) (supplied by SAFC Hitech®) were used as the aluminum and tantalum sources, respectively, whereas DI water was used as the oxygen containing co­reactant. The TMA and H2O were both held at room temperature and delivered using vapor draw, whereas the PDMAT was heated to 75ºC and was transported with the assistance of 100 sccm of argon (BOC 99.998%) using a dip­leg bubbler. The self­limiting growth rates for the Al2O3 and Ta2O5 ALD processes were measured as 0.9 Å/cycle and 0.76 Å/cycle, respectively, based on high­resolution scanning transmission electron microscopy (HR­STEM). Tantalum doping of Al2O3 was realized using delta doping where TMA based ALD cycles (nTMA) (20 ms TMA dose / 5 s purge / 20 ms H2O dose / 5 s purge) were periodically interspersed with PDMAT ALD cycles (nPDMAT) (4 s PDMAT dose / 5 s purge / 20 ms H2O dose / 5 s purge). Throughout the process, the overall argon flow into the reactor was maintained at 200 sccm giving a chamber pressure of approximately 200 mTorr. The overall number of ALD cycles (n) was set to 60 to deposit ~5 nm thick films for band alignment and interface studies. ~10 nm thick samples were grown using n = 120 cycles to investigate the composition and bandgap of the bulk oxide films.

Post deposition rapid thermal annealing (RTA) was performed using Jipelec JetFirst 150 rapid thermal processing system. The samples were annealed at 600ºC for 60 s under nitrogen ambient, which is analogous to the conditions used for the formation of ohmic contacts in the GaN­based HEMT structures using an Au­free Ta/Al/Ta metallization scheme. 

X­ray photoelectron spectroscopy (XPS) measurements were performed using a VG ESCALAB 200i­XL system equipped with a monochromatic Al Ka x­rays (1486.7 eV). All peak binding energies were referenced to the C 1s peak at 285.0 eV to compensate for surface charging. The data analysis of the XPS spectra was carried out using AVANTAGE software. 
Cross­sectional TEM images were acquired using a FEI Titan 80­300 kV scanning transmission electron microscope operating at 200 kV in high­angle annular dark field STEM (HAADF­STEM) and high­resolution bright­field TEM (HR­BFTEM) modes.

n­type Si(100) substrates (supplied by PI­KEM Ltd, test grade) were also used for the fabrication of Au/oxide/Si(100) MOS capacitors to measure the oxide films dielectric properties. Capacitance­voltage (CV) measurements were carried out using an E4980A precision LCR meter. Gold top electrodes of ~1 mm diameter were deposited by sputtering through a shadow mask. After annealing at 600ºC for 60 s in nitrogen (BOC Zero grade), the back metal contact was formed by evaporation of Al on the backside of the Si substrate. The capacitors received a forming gas anneal at 430ºC for 30 min to reduce the density of interface states.



DATA FILE DETAILS: 

FILE TYPES: Numerical data is provided as .CSV files. 
FILE NAMING: File names are directly related to the figure numbers used in the manuscript.
DATA HEADINGS: The first row of each column in the .CSV files contains a clear description of the data within the column together with units in brackets.