Supplemental Material
A study of the impact of gate metals on the performance of
AlGaN/AlN/GaN heterostructure field-effect transistors
Jingtao Zhao, Zhaojun Lin, Quanyou Chen, Ming Yang, Peng Cui, Yuanjie Lv, and
Zhihong Feng
In this supplemental material, the scanning electron microscope with energy
dispersive spectrometer (SEM-EDS) measurements were performed to study the
interaction between the gate metal and the AlGaN interface. And with the measured
capacitance-voltage (C-V) curves and the current-voltage (I-V) characteristics of the
prepared three Ni/Au Schottky contact AlGaN/AlN/GaN HFETs with same structure but
different thicknesses of Au layers, we have analyzed the relationship between the
additional strain of the AlGaN barrier layer with the mass of the gate metals.
With the Schottky contact metals removed, the SEM-EDS measurements were
performed under the gate using FET-Nova Nano SEM 450 and Oxford–X–Max with an
accelerating voltage of 15 KV at room temperature. Fig. S1 is the SEM-EDS composition
maps in the heterostructure material under the different gate metals and the referential
heterostructure material without device processing.
From Fig. S1, it can be observed that the atomic percent of Aluminum for the
referential heterostructure material without device processing is 1.20%. For the
heterostructure materials under Fe, Cu, Ni and Au gate metals, the values of the atomic
percent of Aluminum are close to that in the referential heterostructure material, and Fe,
Cu, Ni and Au atoms are absent in the respective AlGaN Barrier layer. While for the
heterostructure material under Al gate metal, the atomic percent of Aluminum is 6.72%,
much larger than that in the referential heterostructure material. Thus Al Schottky contact
forms a chemical reaction at the interface versus a physical one. This is consistent with
the conclusion in Ref. 1, which claims that for the devices with Al/Au gate metal, the
Al/AlGaN interface undergoes a Ga-Al exchange chemical reaction driven by the large
heat of formation of AlN as compared to that of GaN at room temperature. For the other
four devices, the Schottky contacts form extremely weak chemical reactions at the
interface compared to Al described above.
FIG. S1. The SEM-EDS composition maps in the heterostructure material under the different gate
metals and the referential heterostructure material without device processing. The spectrums 1-5 are
for samples with Al, Fe, Cu, Ni and Au gate metals, respectively. The spectrum 6 is for the referential
heterostructure material.
We prepared three Ni/Au Schottky contact devices with same structure but different
thicknesses of Au layers. To investigate the electrical characteristics, the C-V
measurements were carried out using an Agilent B1520A at 1 MHz, and the I-V
measurements were carried out using an Agilent B1500A semiconductor parameter
analyzer at room temperature. The corresponding electrical characteristics are shown in
Fig. S2, from which it can be seen that the 2DEG sheet carrier density and the intensity of
the PCF scattering are little affected by the mass of the gate metals.
FIG. S2. The measured C-V curves (a), the calculated 2DEG electron density n2D (b) under different
gate biases, the output I-V characteristics (c) and the relationship between the electron mobility of the
2DEG and the applied gate bias (d) for the AlGaN/AlN/GaN HFETs with different thicknesses of the
gate metal at room temperature.
References
1
C. I. Wu, and A. Kahn, J. Vac. Sci. Technol. B. 16, 2218 (1998).