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This paper addresses the fabrication, radiation induced defects and device characteristics of microwave power field effect transistors (FETs) built on 1) high quality diamond surfaces exploiting the 2 dimensional delta channel conductivity, and 2) the surface two dimensional "hydrogen terminated" conduction layer in diamond single crystals grown by CVD.

TiN films were deposited by plasma-assisted atomic layer deposition on AlGaN/GaN structures to investigate the influence of impurities on the performance and stability of Schottky barrier diodes. Oxygen and carbon impurities were reduced, but not completely removed, with increasing TiN growth temperature up to 350 degC. However, the best films still had 4 at% O and 1 at% C impurities as-deposited. TiN films with lower impurity concentrations exhibited lower Schottky barrier heights, providing a way to tailor the properties for different device applications. Films were then exposed to sequential anneals from 400-800 degC in 200 degC increments. X-ray diffraction showed that increasing anneal temperature reduced compressive stress and resulted in higher crystalline quality films. All films maintained similar morphology up to 600 degC, but at 800 degC underwent complete relaxation through fracturing and grain growth that caused significantly rougher films. Despite the change in morphology, TiN gates showed stable operation and low leakage throughout the entire temperature range, while Ni/Au gates failed above 600 degC, suggesting ALD TiN gates could be used in applications where increased thermal stability is required.

Temperature dependent current-voltage characteristics and Schottky barrier height are reported for 65 nm thick TiN films deposited by atomic layer deposition on (-201) b-Ga2O3 and compared with those of reference Pt Schottky contacts. Using thermionic emission theory, a thermionic emission model for both the Pt and TiN Schottky contacts to (-201) b-Ga2O3 was determined. Both contacts had comparable barrier heights of about 1 eV and near-unity ideality factor values, independent of temperature. The TiN contact had about an order of magnitude lower reverse current at room temperature, however, at high temperature the reverse current of the Pt contact was substantially lower (0.27 mA/cm2).

The energy band alignment between atomic layer deposited (ALD) high-k dielectrics of ZrO2 and HfO2 with n-type b-Ga2O3 was evaluated using x-Ray photoelectron spectroscopy. The valence band offset was found to be [?]0.3 +- 0.04 eV and [?]0.5 +- 0.04 eV for ZrO2and HfO2, respectively, which produced type II, staggered gap alignments for both dielectrics with conduction band offsets greater than 1 eV. Capacitance-voltage measurements were conducted on metal-oxide-semiconductor (MOS) diodes and used to extract the dielectric constants (e) of both oxides. ZrO2films had a nearly ideal e of 24.7 (e [?] 25), while HfO2 exhibited a significantly lower e of 14 (e [?] 25-30). These results, combined with the small hysteresis ([?]0.09 eV) in the capacitance-voltage behavior for both films, is indicative of the high quality of these ALD oxides and their interface with the b-Ga2O3 making them potential candidates as gate dielectrics in power devices based on this relatively new ultra-wide bandgap material.

GaN high electron mobility transistors (HEMTs) have the potential to be extremely tolerant of space and weapons of mass destruction radiation found in space and resulting from weapons of mass destruction. AlGaN/GaN HEMTs were fabricated on Si substrates and passivated with plasma enhanced chemical vapor deposition (PECVD) SiN, also HEMTs with in situ SiN and additional PECVD SiN were compared. These samples were exposed to 2 MeV protons, up to 6x1014 cm-2, which resulted in decreased mobility, decreased sheet carrier density, and an increase in dynamic ON-resistance. High resolution scanning transmission electron microscopy revealed roughening of the AlGaN/GaN interface. Off-state pulsed quiescent voltage stress was used to investigate the dynamic ON-resistance of GaN HEMTs before and after radiation. HEMTs with in situ SiN plus PECVD SiN shows improved radiation hardness for dynamic ON-resistance.

The energy band alignment between atomic layer deposited (ALD) high-k dielectrics of ZrO2and HfO2with n-type β-Ga2O3was evaluated using x-Ray photoelectron spectroscopy. The valence band offset was found to be −0.3 ± 0.04 eV and −0.5 ± 0.04 eV for ZrO2and HfO2, respectively, which produced type II, staggered gap alignments for both dielectrics with conduction band offsets greater than 1 eV. Capacitance-voltage measurements were conducted on metal-oxide-semiconductor (MOS) diodes and used to extract the dielectric constants (ɛ) of both oxides. ZrO2films had a nearly ideal ɛ of 24.7 (ɛ ∼ 25), while HfO2exhibited a significantly lower ɛ of 14 (ɛ ∼ 25–30). These results, combined with the small hysteresis (≤0.09 eV) in the capacitance-voltage behavior for both films, is indicative of the high quality of these ALD oxides and their interface with the β-Ga2O3making them potential candidates as gate dielectrics in power devices based on this relatively new ultra-wide bandgap material.

Advanced applications of AlGaN/GaN high-electron-mobility transistors (HEMTs) in high-power RF and power switching are driving the need for insulated gate technology. We present a metal-oxide-semiconductor (MOS) gate structure using atomic-layer-deposited ZrO2as a high-k, high-breakdown gate dielectric for reduced gate leakage and a recessed barrier structure for enhancement mode operation. Compared to a Schottky metal-gate HEMT, the recessed MOS-HEMT structure demonstrated a reduction in the gate leakage current by 4 orders of magnitude and a threshold voltage shift of +6 V to a record +3.99 V, enabled by a combination of a recessed barrier structure and negative oxide charge.