The dielectric permittivity, dielectric quality factor (inverse dielectric loss), and lattice parameter of 140 nm sputtered SrTiO3 films were dependent on the oxygen partial pressure and total chamber pressure (O-2+Ar) during film growth. Films were grown at 25 and 75 mTorr (mT) in an oxygen rich and oxygen deficient sputtering gas environment concurrently on (100) SrTiO3 and (111) Pt/(0001) Al2O3 substrates. Films were deposited on platinized sapphire for electrical characterization and the homoepitaxial films were used as a structural and chemical standard. High resolution triple axis x-ray diffraction results showed an increase in mismatch between the film and substrate (200) peak in homoepitaxial SrTiO3 films with higher total growth and lower oxygen pressures. Dielectric quality factors of the SrTiO3 films on platinized sapphire at 1 MHz for the 25 mT (50 sccm Ar/50 sccm O-2), 25 mT (90 sccm Ar/10 sccm O-2), 75 mT (50 sccm Ar/50 sccm O-2), and 75 mT (90 sccm Ar/10 sccm O-2) film growths were 320, 251, 209, and 102, respectively; likewise, the dielectric constants follow as 241, 230, 220, and 170, respectively. Improved film dielectric properties were observed for films closer to stoichiometric SrTiO3. (C) 2003 American Institute of Physics.

We investigated the suitability of ZrO2 as a high-k dielectric for GaN material systems. Thin Zr films (4 nm) were deposited by electron-beam evaporation at room temperature oil n-type GaN and Al(0.22)Gao(0.78)N (29 nm)/GaN high electron mobility transistor (HEMT) structures. The Zr-coated samples were subsequently oxidized at temperatures in the range of 200-400 degrees C in an ozone environment. Atomic force microscopy studies after oxidation show that the ZrO2 forms a conformal layer on the underlying GaN template. Cross-section transmission electron microscopy studies showed little intermixing of the ZrO2 with the AlGaN/GaN. The relative dielectric constant of the ZrO2 was determined to be 23. In comparison with HEMTs with bare gates (no dielectric between the gate metal and AlGaN), the HEMTs with ZrO2 showed two to three order of magnitude reduction in gate leakage current. Optimization of the HEMT process on sapphire substrates with ZrO2 under the gates yielded devices with powers of 3.8 W/mm and 58% power-added efficiency at 4 GHz. (c) 2006 American Vacuum Society.

Titanium dioxide (TiO2, with the rutile structure) was grown on (0001) oriented GaN and (0001) Al0.33Ga0.67N/GaN heterostructure field effect transistor (HFET) structures by molecular beam epitaxy. X-ray diffraction showed (100)TiO2 parallel to (0001)(GaN(AlGaN)) and [001](TiO2) parallel to (GaN(AlGaN)) with three rotational variants of the TiO2. Transmission electron microscopy of 50 nm thick TiO2 films on GaN and AlGaN/GaN showed sharp interfaces with no intermixing or reaction between the oxide and semiconductor. The TiO2 exhibited a columnar film microstructure with a lateral domain size of a few nanometers parallel to (10 (1) over bar)(TiO2) and a few tens of nanometers parallel to 00160 2 2 Metal-oxide HFIAs with 50 nm thick TiO2 dielectric layers under the gate were processed and compared to HFETs without the TiO2 dielectric layer. The transconductance of the HFETs with TiO2 was 140 MS/mm, approximately 20% less than HFETs with no dielecric, and the pinchoff voltages of the two stuctures were comparable. The dielectric constant of the TiO2 was similar to 70. The gate leakage current of the HFETs with ,TiO2, similar to 4 X 10(-6) mA/mm at. 50 V, was approximately 4 orders of magnitude lower than that of the. HFETs with no dielectric. Band offset measurements were performed using x-ray photoelectron spectroscopy, and the valence band of the rutile TiO2 and the GaN nearly line up. (c) 2005 American Vacuum Society.