Research On Novel Structure Of GaN-on-Si Lateral Power Diode

In the last decade, the new generation semiconductor material gallium nitride(GaN) has been intensively studied because its intrinsic electrical properties such as wide band gap and high thermal conductivity are much higher than those of silicon. Moreover, the GaN-based heterostructure field-effect transistors have a high density of two-dimensional electron gas channel in which the electron mobility is much higher than that of a MOSFET or MESFET, which makes the GaN-based devices a promising candidate in future applications in high frequency and high power field. Diode is one of the most important devices in the field of power semiconductor and it is widely used in power systems such as switching circuit, rectifying circuit, amplitude limiting circuit, drive circuit, accumulator and so on. Compared to Si Schottky Barrier Diode, a GaN power diode behaves better for its lower turn-on voltage, lower on-resistance, higher breakdown voltage and better thermal conductivity, which further reduces the energy consumption and improve the reliability of the circuit. The present GaN devices, however, do not achieve the level it should have in the terms of turn-on voltage, on-resistance and breakdown voltage for lack of theories and good process technologies. This is the motivation we do more research on the new structure and process technologies of GaN power diodes.In this study, a new device structure named MG-HAD is proposed. A hybrid anode of ohmic metal and trench-barrier-gate metal is used in this structure. The 2DEG channel is opened by a low turn-on voltage on the gate metal thus electrons can flow from the cathode to the anode. The MG-HAD has three main advantages compared to conventional structures: 1. The turn-on voltage can be easily modulated which allows customizing according to demand. 2. Ohmic contact in anode decreases the on-resistance. 3. The trench-barrier-gate makes the electric field near the anode more uniform which increases the breakdown voltage.To verify the feasibility of the design of MG-HAD, an experiment was conducted. In this experiment, two critical process technologies ohmic contact and two-step etching were optimized. The devices fabricated behaves very well in tests of IV/BV and temperature stability.It is found in IV test that MG-HADs have a turn-on voltage as low as 0.6V, which breaks through the bottleneck of traditional Ga N SBDs. Besides, MG-HADs’ reverse leakage current is below 10μA/mm. It is remarkable that the devices behaves well at high temperature like 150°C, at which the breakdown voltage reaches 600 V compared to over 1100 V at room temperature.