Wei-Jen Hsueh

Surface Passivation of GaSb(100) Using Molecular Beam Epitaxy of Y2O3 and Atomic Layer Deposition of Al2O3: A Comparative Study

Y2O3 and Al2O3 were deposited onto GaSb(100) surfaces by molecular beam epitaxy and atomic layer deposition, respectively. Angle-resolved X-ray photoelectron spectroscopy and electrical measurements were used to probe the two oxide/semiconductor interfaces, which yielded very different behaviors. Highly surface-sensitive scans showed traces of SbOx and AsOx at the Y2O3 surface, which were removed during subsquent ALD Al2O3. The deposition of Y2O3 led to true inversion as indicated in capacitance–voltage (C–V) characteristics, small hysteresis and frequency dispersion, and low gate leakage. In contrast, for Al2O3/GaSb, the GaSb remained virtually intact, with Al2O3 bonding to the residual As, leading to poor C–V characteristics.

Effects of GaSb surface preparation on the characteristics of HfO2/Al2O3/GaSb metal-oxide-semiconductor capacitors prepared by atomic layer deposition

The electrical, structural, and chemical properties of HfO2/Al2O3/GaSb metal-oxide-semiconductor capacitors (MOSCAPs) fabricated on Sb-rich (2 × 5) and Sb-stabilized (1 × 3) surfaces by atomic layer deposition are characterized. A combination of the transmission electron microscopic, x-ray photoelectron spectroscopic, and atomic force microscopic observations shows that the Sb-rich surface, with its excessive Sb atoms and clusters, leads to island deposition of the dielectric materials and results in the high leakage current of the MOSCAPs. For the MOSCAPs fabricated on the Sb-stabilized (1 × 3) surface, a density of interface traps as low as 8.03 × 1011 cm−2 eV−1 near the valence band and 1.86 × 1012 cm−2 eV−1 at the midgap is obtained as estimated by the conductance method.

Suppressing Ge diffusion by GaAsSb for molecular beam epitaxy of InGaAs on Ge

We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb layer also provides a smoother surface morphology with its root mean square roughness of 0.664 nm. Using a GaAsSb step-graded buffer (SGB) and an AlGaAsSb high resistivity buffer, we are able to grow a 200 nm p-type InGaAs layer on Ge and yield hole mobility of 37.5 cm²/V-s at 300K and 53.1 cm²/V-s at 77K with hole concentration of 2.6×10¹⁹ cm^-3 and 1.2×10¹⁹ cm^-3, respectively.

High performacne InAs/AlSb HEMT with refractory iridium Schottky gate metal

In the work, a novel approach in fabricating high-performance of InAs/AlSb high electron mobility transistors using iridium (Ir) gate technology was proposed and investigated. The Ir-gate exhibited a superior metal work function which was beneficial for increasing Schottky barrier height (ØB) of InAs/AlSb heterostructure from 0.54 to 0.58 eV. The Ir-gate InAs/AlSb HEMT exhibited a Vth of -0.9 V, a maximum drain current of 270 mA/mm, and a peak transconductance of 420 mS/mm. In contrast, the Vth of Ti-gate InAs/AlSb HEMT was - 1.5 V, a maximum drain current of 257mA/mm, and a peak transconductance of 280mS /mm, respectively. It was suggested that Ir interface presented a high potential for high power transistor applications.