Papers by Keyword: Semi-Insulating Substrate

Abstract: We fabricated a 0.5-μm-gate MESFET on a bulk 4H-SiC semi-insulating substrate using ion implantation for the channel and contact regions. Our device design used a thin, highly doped channel layer, which was implanted at single energy to improve the device’s RF characteristics. The electrical characteristics of the ion-implanted MESFET annealed at 1700°C were better than those of the ion-implanted MESFET annealed at 1300°C. The fabricated ion-implanted MESFET has a maximum transconductance of 32.8 mS/mm and an fT/fmax of 9.1/26.2 GHz. The saturated output power was 26.2 dBm (2.1 W/mm) at 2 GHz. These values were the same as those of the conventional epitaxial MESFET with a recessed gate.

Abstract: The electrical characteristics of a SiC-MESFET are affected by the channel structure characteristics, such as impurity density and thickness. MESFETs fabricated with ion implantation technique, can form thinner and higher doped channel layers than those fabricated with conventional epitaxial growth, thus improve RF characteristics of MESFETs. We calculated the doping profile of the channel layer for an ion implanted SiC-MESFET using a simulator and then fabricated a SiC-MESFET with the same doping profile as obtained from the simulation. The ion implanted SiC-MESFET operated successfully and had the same electrical characteristics as the epitaxial SiC-MESFET. We demonstrated the effectiveness of one-step implantation channel layer for the ion implanted SiC-MESFET.

Abstract: We fabricated a 0.5-μm gate MESFET on a bulk semi-insulating 4H-SiC substrate by using ion implantation for the channel layer and contact region. Nitrogen ions were implanted to obtain a 0.25-μm-thick box-shaped profile with a doping density of 3.0×1017/cm3 for the channel region and to obtain a 0.2-μm-thick box-shaped profile with a doping density of 2.0×1020/cm3 for the contact region. Activation annealing is done in argon ambient at 1300 °C for 30 minutes. A 0.5- μm gate MESFET with 100-μm gate width showed a cut-off frequency of 7.5 GHz and a maximum oscillation frequency of 22.2 GHz. And its saturated output power was 25 dBm (3.16 W/mm), power gain was 6.7 dB and PAE was 15.7%.

Abstract: Quantitative assessment of the influence of deep traps in semiinsulating (SI) SiC substrates on transient behavior and substrate leakage current of SiC MESFET is reported. Twodimensional device simulation confirmed that favorable reduction of the current-collapse happens when a fully depleted buffer is used. Simultaneously, the high-purity buffer causes an undesirable increase of the current bypassing the physical channel. A similar and even more pronounced effect is observed when very high purity SI substrates are used. The deep level-induced transient behavior disappears for the concentration of deep acceptor traps below the order of 1x1015 cm-3. However, this low trap concentration results in a virtual inability to pinch-off the channel even at very high gate biases. It has been demonstrated that the electric field preventing electron injection from thechannel into the substrate is very sensitive to the initial charge state of the traps prior to device biasing, which in turn is determined by the energy position of the deep levels in the substrate.