Jesse B. Tucker

Structure of stacking faults formed during the forward bias of 4H-SiC p-i-n diodes

Using site-specific plan-view transmission electron microscopy (TEM) and light emission imaging, we have identified stacking faults formed during forward biasing of 4H-SiC p-i-n diodes. These stacking faults (SFs) are bounded by Shockley partial dislocations and are formed by shear strain rather than by the condensation of vacancies or interstitials. Detailed analysis using TEM diffraction contrast experiments reveal SFs with leading carbon-core Shockley partial dislocations as well as with the silicon-core partial dislocations observed in plastic deformation of 4H-SiC at elevated temperatures. The leading Shockley partials are seen to relieve both tensile and compressive strain during p-i-n diode operation, suggesting the presence of a complex inhomogeneous strain field in the 4H-SiC layer.

Microwave power SiC MESFETs and GaN HEMTs

Abstract We have fabricated SiC metal semiconductor field effect transistors (MESFETs) with more than 60 W of output power at 450 MHz from single 21.6 mm gate periphery devices (2.9 W/mm) and 27 W of output power at 3 GHz from single 14.4 mm SiC MESFET devices (1.9 W/mm). We have also demonstrated more than 6.7 W/mm CW power from 400 μm GaN/AlGaN high electron mobility transistors devices for X band (10 GHz) applications. These excellent device performances have been attributed to the improved substrate and epitaxial films quality, optimized device thermal management, and enhanced device fabrication technologies. The substrates and epitaxial films from different sources were compared and some showed significant less SiC substrate micropipes confirmed by X-ray topography and epitaxial defects characterized by optical defect mapping.

Ion-Implantation in Bulk Semi-Insulating 4H-SiC

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H–SiC at various doses to obtain uniform implant concentrations in the range 1×1018–1×1020 cm−3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ⩽1019 cm−3 is limited by carrier ionization energies, whereas for the 1020 cm−3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing t...

High temperature Hall effect sensors based on AlGaN∕GaN heterojunctions

We report on AlGaN∕GaN heterojunction structures for use in Hall effect sensors working over a wide range of temperatures. Room temperature current-related magnetic sensitivity of 55V∕AT at a sheet resistance below 300Ω∕sq and very low temperature cross sensitivity of 103ppm∕°C up to 300°C were obtained for a square-shaped Hall effect sensor. The active layer of the Hall effect sensor is the two-dimensional electron gas formed at the Al0.3Ga0.7N and GaN heterointerface caused by the gradient in the total polarization between the AlGaN barrier and the GaN buffer layer, which results in the positive polarization induced interface charge attracting free electrons. The temperature-dependent transport properties of the heterojunction were analyzed by Hall measurement. The drop of its electron mobility from room temperature to 300°C is mainly due to the enhanced polar optical scattering, while the very stable sheet carrier density contributes to the excellent temperature cross sensitivity of the Hall effect sensor.

Fully ion implanted MESFETs in bulk semi-insulating 4HSiC

Abstract MESFETs ( n -channel) were fabricated in semi-insulating bulk 4HSiC by ion implantation of both the source/drain and the channel regions, using an aluminum Schottky gate metal and nickel ohmic contacts. Nitrogen ion implantation was performed at room temperature to a depth of 300 nm at a volumetric concentration of 6×10 17 cm −3 for the channel region and 2×10 19 cm −3 for the source/drain. The implants were activated by annealing at 1450 °C for 15 min using an AlN encapsulant. The bulk mobility of the channel implant was found to be 240 cm 2 /V s, while the effective channel mobility of the devices was measured to be less than 58 cm 2 /V s. For a typical device with a 2-μm gate length, the pinch-off voltage was 18 V, and the drain saturation current was approximately 40 mA. Devices exhibited only a small change in their DC characteristics over the temperature range 25–350 °C.

Characteristics of planar n-p junction diodes made by double-implantations into 4H-SiC

Double implantation technology consisting of deep-range acceptor followed by shallow-range donor implantation was used to fabricate planar n/sup +/-p junction diodes in 4H-SiC. Either Al or B was used as the acceptor species and N as the donor species with all implants performed at 700/spl deg/C and annealed at 1650/spl deg/C with an AlN encapsulant. The diodes were characterized for their current-voltage (I-V) and capacitance-voltage (C-V) behavior over the temperature range 25/spl deg/C-400/spl deg/C, and reverse recovery transient behavior over the temperature range 25/spl deg/C-200/spl deg/C. At room temperature, the B-implanted diodes exhibited a reverse leakage current of 5/spl times/10/sup -8/ A/cm/sup 2/ at a reverse bias of -20 V and a carrier lifetime of 7.4 ns.

Nitrogen and phosphorus implanted MESFETs in semi-insulating 4H-SiC

Abstract Nitrogen and phosphorus ion implantation were used to fabricate 2 μm gate length, n-channel Metal-Semiconductor Field-Effect-Transistors (MESFETs) in semi-insulating bulk 4H-SiC. In order to create the channel region, either nitrogen or phosphorus ion-implantations was performed to a depth of 300 nm at room temperature to a volumetric concentration of 5×10 17 cm −3 . The source/drain regions were created by nitrogen implantation to a volumetric concentration of 2×10 19 cm −3 , regardless of the species used for the channel implantation. Annealing for a duration of 15 min at 1450 °C (for nitrogen-implanted channels) or 1500 °C (for phosphorus-implanted channels) activated the implants. This study utilized aluminum Schottky gates for the FETs. Both the nitrogen and phosphorus-implanted channel MESFETS exhibited pinch-off voltages at approximately 18 V and the drain saturation currents between 30 and 40 mA.

Partial Dislocations and Stacking Faults in 4H-SiC PiN Diodes

Using plan-view transmission electron microscopy (TEM), we have identified stacking faults (SFs) in 4H-SiC PiN diodes subjected to both light and heavy electrical bias. Our observations suggest that the widely expanded SFs seen after heavy bias are faulted dislocation loops that have expanded in response to strain of the 4H-SiC film, while faulted screw or 60° threading dislocations do not give rise to widely expanded SFs. Theoretical calculations show that the expansion of SFs depends on the Peach-Koehler (PK) forces on the partial dislocations bounding the SFs, indicating that strain plays a critical role in SF expansion.

ION-IMPLANTATION IN SIC AND GAN

Abstract The electrical activation behavior of N- and Al-implantations in bulk V-doped semi-insulating 4H–SiC is similar to that in 4H–SiC epitaxial layers. The As- and Sb-implantations in p-type 6H–SiC epitaxial layers showed out-diffusion behavior with room-temperature sheet carrier concentrations of

Material and n–p junction characteristics of As- and Sb-implanted SiC

Abstract Single and multiple energy As and Sb implantations were performed into p-type 6H–SiC epitaxial layers at room temperature (RT) and 800°C. Secondary ion mass spectrometry measurements showed severe implant loss for annealing temperatures >1500°C. Rutherford backscattering spectroscopy/channeling (RBS/C) measurements indicated a high degree of residual lattice damage for RT implantations even after 1600°C annealing while less damage was detected in 800°C implanted samples. Electrical activations (ratios of sheet carrier concentrations to implant doses) of 11 and 20% were measured for 800°C As and Sb implantations annealed at 1500°C, respectively. The Schottky capacitance–voltage profiling measurements indicated substitutional concentrations in the low 1018 cm−3 range for both As and Sb. Based on the experimental data, carrier ionization energies of 130 and 88 meV were estimated for As and Sb donors, respectively. Vertical n–p junction diodes were made by using multiple energy As and Sb implanted epitaxial layers. Elevated temperature As implanted diodes exhibited a room temperature reverse leakage current of ≈8×10−8 A/cm2 with no passivation at −100 V bias and a forward series resistance of 460 Ω.