High-Temperature Performance in AlGaN/GaN Heterostructure Field Effect Transistors
Narihiko Maeda, Tadashi Saitoh, Kotaro Tsubaki, Toshio Nishida, and Naoki
Kobayashi
Physical Science Laboratory
@The GaN-based material system is very promising for high-temperature,
high-voltage, and high-power microwave applications, because of the large
breakdown electric field and the large electron saturation velocity in this
material system. We have fabricated AlGaN/GaN heterostructure field effect
transistors (HFETs) whose I-V characteristics have exhibited both excellent
current saturation and sufficient pinch-off characteristics up to a high
temperature of 400 C.
The layer structure of fabricated HFETs was 300 A Al0.15Ga0.85N/1 mm GaN/1000 A
AlN/SiC(0001) [see Frontispiece]. The gate length and gate width were 2 and 20
mm, respectively. Since a large piezoelectric effect exists at the AlGaN/GaN
heterointerface, unrelaxed AlGaN/GaN heterostructures with large lattice strains
are capable of containing very high two-dimensional electron gas densities
larger than 1 L 1013 cm-2 [1]. Figure 1 shows the I-V characteristics of the
fabricated device at 400 C. Sufficient pinch-off characteristics have been
obtained as well as excellent current saturation characteristics. Obtaining
pinch-off characteristics are indispensable for practical uses of the devices,
because reported insufficient pinch-off characteristics should lead to
degradation in the RF performance, that in the breakdown voltage, and increase
in the noise figure. Pinch-off characteristics shown in Fig. 1 have been
obtained as the result of reduced crystal defects and reduced etching damage in
the devices. Figure 2 shows the temperature (T) dependence of the
transconductance (gm). Although gm decreases with increasing T, the degradation
rate in gm is shown to be relatively small above 300 C, which is a favorable
feature for high-temperature applications. We are especially interested in the
application of the devices for satellite microwave communications.
[1] N. Maeda, T. Nishida, N. Kobayashi, and M. Tomizawa, Appl. Phys. Lett.
73(1998) 1856.
[2] N. Maeda, T. Saitoh, K. Tsubaki, T. Nishida, and N. Kobayashi, to be
published in Jpn. J. Appl. Phys., Part 2 (1999).
Fig. 1:I-V
characteristics at 400 C.
Fig. 2:Temperature
(T) dependence of transconductance (gm)