In recent years there has been intense development of new semiconductor materials (including so-called semi-insulating materials) for achieving semiconductor devices having special features, such as high-frequency characteristics, light emission characteristics, and withstand voltage characteristics. Among semiconductor materials, those with so-called semi-insulating properties in an intrinsic state, for example silicon carbide (SiC), gallium nitride (GaN), and gallium arsenide (GaAs), have higher hardness and are less susceptible to chemicals than silicon (Si), which is the most typical of semiconductor materials, and because these semiconductors have a large band gap, they have promise for future applications in next-generation power devices, high-frequency devices, and devices operating at high temperature, for example, utilizing their high withstand voltages.
Semiconductor power devices utilizing these wide band gap semiconductor materials include high withstand voltage Schottky diodes, MESFETs (Metal Semiconductor Field Effect Transistors), and MISFETs (Metal Insulator Semiconductor Field Effect Transistors), for example.
An example of a Schottky diode and a MISFET are provided here as conventional examples of a semiconductor power device.
FIG. 11 is a cross-sectional view showing the schematic structure of a conventional Schottky diode using silicon carbide (SiC). As shown in FIG. 11, numeral 101 denotes an n+ SiC substrate of approximately 100 μm thickness that has been doped with a high concentration of nitrogen (N), which is an n-type carrier, numeral 102 denotes an n− SiC layer that is approximately 10 m thick and has been doped to a low concentration of nitrogen (N), which is an n-type carrier, numeral 103 denotes a Schottky electrode made of a Ni alloy, numeral 104 denotes an ohmic electrode made of a Ni alloy, and numeral 105 denotes a guard ring made of SiO2. In this diode, when voltage is applied between the Schottky electrode 103 and the ohmic electrode 104 so that the Schottky electrode 103 has a higher potential than the ohmic electrode 104 (forward voltage), current flows between the Schottky electrode 103 and the ohmic electrode 104, and when voltage is applied between the Schottky electrode 103 and the ohmic electrode 104 so that the ohmic electrode 104 has a higher potential than the Schottky electrode 103 (reverse voltage), current does not flow between the Schottky electrode 103 and the ohmic electrode 104. That is, this Schottky diode has a rectification characteristic that allows current to flow in accordance with forward voltage, but blocks current with respect to reverse voltage.