Heterostructure Field Effect Transistor Types with Novel Gate Dielectrics

Abstract

In this paper we report on results obtained for different AlGaN/GaN heterostructure field effect transistors (HFET) applying a recently developed photooxidation technique. We have processed and characterized MOS-HFETs in which a photoanodic oxide, a PECVD deposited SiO 2 layer, or a combined stack of the photoanodic oxide followed by SiO 2 (tandem-approach) is used as gate dielectric. All tandem-MOS-HFET devices have in common a large gate voltage swing and a broad transconductance peak. Additionally, the leakage and gate currents are several orders of magnitude smaller than for the Schottky gate HFETs and are in the range of pA/mm. Tandem MOSH-FET devices achieved values of 465 mA/mm in enhancement mode and 46 mS/mm for the drain current I Dmax and transconductance g m , respectively. These values are about 50% (I Dmax ) and 15% (g m ) higher than for the HFETs processed on the same wafer. Thermal oxidation at 900 C for 15 min before SiO 2 deposition leads to a normally off transistor type.

Formation of Thin Native Oxide Layer on n-GaN by Electrochemical Process in Mixed Solution with Glycol and Water

“…For oxidation, Rotter et al 4) carried out a photo-assisted electrochemical process on the n-GaN surface in KOH solution under potentiostatic control. Similarly, Mistele et al 5) fabricated and characterized AlGaN/GaN high electron mobility transistors in which photoanodically grown oxide layers were used as gate dielectrics.…”

“…6) Unlike the processes in alkaline solutions used the previous studies, 4,5) the present method enables us to form a thin oxide layer on the GaN surface with a nearly neutral condition in the solution, which is important to avoid unexpected etching reactions on the oxidized GaN surface during the electrochemical process.…”

Influence of Process Technology on DC-Performance of GaN-Based HFETs

“…The combination of the properties of the 2DEG at the heterojunction and the introduction of a thin insulating layer lead to the realization of MOSHFET devices with good DC and HF properties and very low leakage currents [3]. Our group has experienced that by the introduction of photoelectrochemically (PEC) grown Ga 2 O 3 as well as by the introduction of a SiO 2 layer with different pre-treatments, the DC-performance improves and the maximum drain current I Dmax increases [4,5]. Next, Eastman et al report of a sensitive behavior of a SiN x passivation layer with respect to the output RF power of AlGaN/GaN HFETs [6,7].…”