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Normally-off AlGaN/GaN/AlGaN double heterostructure FETs with a thick undoped GaN gate layer

: Benkhelifa, F.; Müller, S.; Polyakov, V.M.; Ambacher, O.


IEEE Electron Device Letters 36 (2015), No.9, pp.905-907
ISSN: 0741-3106
ISSN: 0193-8576
Journal Article
Fraunhofer IAF ()
normally-off; AlGaN/GaN/AlGaN DHFET; AlGaN back-barrier; thick undoped GaN gate layer; polarization charge engineering

In this letter, we report on polarization charge engineering enabling normally-off operation for a double-heterostructure Al(0.26)Ga(0.74)N/GaN/Al(0.07)Ga(0.93)N-based field effect transistors (DHFETs) using a 35-nm-thick undoped GaN layer underneath the gate metallization. The combined effect of the negative polarization charge induced by the AlGaN back barrier and the undoped GaN gate layer ensures the total depletion of the channel, and provides a positive thres-hold voltage. The fabricated DHFET exhibits normally-off operation with a threshold voltage of 1.2 V, a maximum drain current density of 370 mA/mm, and a high ON/OFF current ratio of 10(7), at a gate bias of 7 V. A transistor with gate-drain distance of 6µm demonstrates 300 V off-state breakdown voltage.