Search

The influence of bulk traps in different regions of 4H-SiC bipolar junction transistors (BJTs) is investigated. The investigation is based on experimental results obtained by implanting up to \10^11\cm^-2 fluences of helium ions in the collector region. The results indicate that implantations, creating point defect concentrations in the range of the doping level, produce a sufficiently high concentration of traps to reduce the carrier concentration in this specific region. These traps degrade the device characteristics and are irrecoverable up to 500 ^\circ\C annealing. The experimental results are qualitatively analyzed by device simulations using a 2D numerical computer-aided design tool (TCAD). Systematic simulations are then performed by introducing traps at different locations in the BJT (i.e., emitter, base, and collector regions). The results indicate that the device performance is highly dependent on the defect concentration in the base region. The defects at different levels inside the collector also influence the device by producing a compensated layer in the material. However, the same concentration of defects (i.e., \sim\10^15\ \cm^-3) has less influence in the emitter region. [ABSTRACT FROM AUTHOR]

Degradation of \SiO2 surface passivation for 4H-SiC power bipolar junction transistors (BJTs) as a result of ion irradiation has been studied to assess the radiation hardness of these devices. Fully functional BJTs with 2700 V breakdown voltage are implanted with 600 keV helium ions at fluences ranging from \1 \times \10^12 to \1 \times \10^16\ \cm^-2 at room temperature. These ions are estimated to reach the \SiO2/ \SiC interface. The current–voltage characteristics before and after irradiation show that the current gain of the devices starts degrading after a helium fluence of \1\times \10^14\ \cm^-2 and decreases up to 20% for the highest fluence of ions. Simulations show that the helium ions induce ionization inside the \SiO2, which increases the interface charge and leads to a degradation of the BJT performance. Thermal annealing of the irradiated devices at 300 ^\circ \C, 420 ^\circ\C, and 500 ^\circ\C further increases the amount of charge at the interface, resulting in increased base current in the low-voltage range. [ABSTRACT FROM AUTHOR]

A high gamma radiation hardness of 4H-SiC circuits is performed. The OR NOR circuits are based on emitter coupled logic (ECL), using integrated bipolar NPN transistors. Gain degradation in individual bipolar junction transistors (BJT) is minimal up to a dose of 38 Mrad (SiO2), but for the dose of 332 Mrad (SiO2) a degradation of 52% is observed. The SiC BJTs show higher radiation hardness than existing Si-technology and high stability under temperature stress. It is proposed that the oxide charge-dominated recombination is the key base current recombination mechanism contributing to gain degradation. An improvement in the gain is seen after annealing at 400 °C for 1800 s due to the possible annealing of some of the oxide defects contributing to the oxide charge. [ABSTRACT FROM PUBLISHER]