Fast true vertical GaN transistors for direct driving of diode lasers (PioneerGaN)

Goal of the PioneerGaN project is to develop fast switching, true vertical GaN power transistors together with a subsequent verification of these devices for driving diode lasers to create ns-type light pulses.

Schematic cross section through an inversion type vertical GaN MISFET
Fig. 1: Schematic cross section through an inversion type vertical GaN MISFET.
First results obtained on circular transistor test structures
Fig. 2: First promising results obtained on circular transistor test structures.

The devices to be developed rely on the inversion type of gate drive mechanism. Thus, the vertical electron flow from a top source electrode to the GaN substrates acting as the drain terminal of the devices (see fig. 1) can be controlled. This transistor arrangement offers the potential to be directly integrated with a diode laser chip in such a way that low loss and fast laser pulsing will be possible. The close cooperation between companies and research institutes located in Berlin and Poland bundles the respective expertise towards developing intrinsically vertical GaN power switching transistors intended for laser drivers.

For vertical transistor realization critical technological steps are to be developed and combined to a complete process flow. The epitaxial realization of the basic epitaxial stack in conjunction with the technology of the vertically oriented gates decisively determines the functionality of the complete devices. It is therefore important that all process steps are effectively adapted to each other. The vertical gate technology, for example, requires a well-adapted sequence of plasma etching gate insulator deposition and gate metallization. The complete process flow from epitaxy to the final integration with a diode laser will be accomplished at FBH. Critical process steps will be performed by partners such as SENTECH instruments. The company is in charge of gate insulation deposition by applying atomic layer deposition of Al2O3. The GaN substrates for full vertical integration will be provided by the Polish company SEEN semiconductors. The research institution EIT+ in Wroclaw will take care of dedicated material characterizations and subsequently provide epitaxial device structures basing on Molecular Beam Epitaxy (MBE) – in a complementary manner to the Metal Organic Vapor Phase Epitaxy (MOCVD) prevailing at FBH.

Fig. 2 summarizes first very promising process results obtained on simple test transistors with circular layout.

The project is partly financed by the European Regional Development Fund (ERDF), funding period: 01.09.2015 – 31.08.2018.