Abstract
p-type GaSb metal–oxide–semiconductor capacitors with thin InAs surface capping layers were prepared on Si(001) substrates. Epitaxial structures with superlattice metamorphic buffer layers were grown by molecular beam epitaxy. Chemical surface treatment and atomic layer deposition methods were employed for a semiconductor surface passivation and Al2O3 high-k oxide fabrication, respectively. Capacitance-voltage measurements and scanning and transmission electron microscopies were used to correlate electrical properties with the oxide-semiconductor interface structure of the capacitors. Unexpectedly, fast minority carrier response present down to liquid nitrogen temperature was observed in the capacitors passivated by an ammonium sulfide solution. This fast response was found to be related to etch pitlike surface morphology developed upon chemical passivation at the surface steps formed by microtwins and antiphase domain boundaries. Preferential InAs etching by ammonium sulfide at the surface defects was confirmed by analytical TEM studies. Very low activation energy of minority carrier response suggests the presence of electron sources under the gate; they result from growth-related surface defects that give rise to potential fluctuations of as high as half the GaSb bandgap.
Highlights
Group III-Sb compound semiconductors have been attracting much attention as channel materials for high speed and low power consumption complementary metal–oxide–semiconductor (CMOS) transistors as a replacement of current silicon CMOS technology.[1,2,3] GaSb has the highest hole mobility (∼850 cm2/V s) among the III-V semiconductors and low in-plane hole effective mass in the 2D channel.[4]
This fast response was found to be related to etch pitlike surface morphology developed upon chemical passivation at the surface steps formed by microtwins and antiphase domain boundaries
Very low activation energy of minority carrier response suggests the presence of electron sources under the gate; they result from growth-related surface defects that give rise to potential fluctuations of as high as half the GaSb bandgap
Summary
Group III-Sb compound semiconductors have been attracting much attention as channel materials for high speed and low power consumption complementary metal–oxide–semiconductor (CMOS) transistors as a replacement of current silicon CMOS technology.[1,2,3] GaSb has the highest hole mobility (∼850 cm2/V s) among the III-V semiconductors and low in-plane hole effective mass in the 2D channel.[4]. Currently efforts are shifting toward more flexible ex situ processes, such as atomic layer deposition (ALD) of gate oxide[17–19] with accompanying semiconductor surface passivation methods, such as using HCl, HF, (NH4)2S, NH4OH, or hydrogen plasma.[18–23]. The interface quality improvement by an InAs capping layer in Al2O3/InAs/GaSb gate stack was reported,[25–27] but most of the passivation experiments were done when III-Sb layers were grown on either GaSb or GaAs substrates. We studied the interface properties of p-type Al2O3/InAs/GaSb chemically passivated gate stacks prepared on Si substrates to obtain correlations between the interface passivation technologies, defect formation, and electrical properties. The growth process was initiated with 5 min of Si surface soaking under an Sb2 flux, followed by deposition of three monolayers of a p-type AlSb nucleation layer grown at 500 °C, 200 nm of p-type GaSb/AlSb superlattice (SL) at 470 °C, and four layers of InSb quantum dots (QDs) at 400 °C, all forming a metamorphic buffer. Capacitance-voltage (C-V) measurements, x-ray photoelectron spectroscopy (XPS), and scanning and transmission electron microscopies were employed to correlate the electrical and the structural properties of the capacitors
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