document: Ge (100) wafers (n- and p-type) were cleaned in ultra high vacuum (<10−6mbar) at 500°C and 600°C for 10min to evaporate any native oxide and so achieve an oxide free surface. Subsequently, wafers were exposed to an Al flux for a range of times to deposit ultrathin Al layers. The samples were then oxidized at ambient temperatures in the MBE load lock to produce Al2O3 layers. The samples were transferred within 1min to an Oxford Instruments OpAL reactor and thin films of HfO2 were deposited on the Al2O3 using atomic layer deposition (ALD). The HfO2 depositions used a [(CpMe)2HfOMeMe] precursor coupled with an O2 plasma as the oxidizing species. Between 30 and 130 ALD cycles were used to grow HfO2 thicknesses from 1.6 to 7nm at 250°C. For electrical measurements, circular gold contacts of area 1.96×10−3cm2 were deposited onto the films to form MOS gate electrodes and Al was deposited on the back of the Ge wafers to provide an ohmic contact. After preliminary measurements, the samples were annealed in forming gas (FGA) at 350°C for 30min. The oxide leakage current was measured using a Keithley 230B voltage source and Keithley 617B electrometer. The HP 4192A low frequency (LF) impedance analyzer at small signal frequencies between 100Hz to 1MHz was used to perform high frequency capacitance–voltage (HF CV) measurements.
doc_bio_tags: O O B O O O O B I I I I O O O O O O O O B I I I O O O O B I I O B O O O O B O O O O O O O O O B O O B O O B O O O O O B I I O O B O O B O O O O O O B I I I O O B O B O O O O B O B I I B O B O O O O O O O O B I O O B I O O O O B O O O O B I I O O O O O O O B I B I I O O O O O O O B O O B I I O B O O O O O O O B I O O O B I O O O O B O B I I I B O O O O O B I I O B O O B I I I O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O
extractive_keyphrases: al al2o3 ald annealed in forming gas atomic layer deposition circular gold contacts cleaned in ultra high vacuum electrical measurements evaporate any native oxide fga films ge wafers grow hfo2 thicknesses hfo2 keithley 230b voltage source keithley 617b electrometer mbe load lock measured mos gate electrodes o2 plasma ohmic contact oxford instruments opal reactor oxide free surface oxide leakage current oxidized oxidizing species samples wafers
abstractive_keyphrases: al2o3 layers al flux [(cpme)2hfomeme] precursor forming gas ge (100) wafers hfo2 depositions high frequency capacitance–voltage (hf cv) measurements hp 4192a low frequency (lf) impedance analyzer n- and p-type native oxide produce al2o3 layers thin films of hfo2 to perform high frequency capacitance–voltage (hf cv) measurements ultra high vacuum ultrathin al layers