Xue Baiqing

The Impact of HCl Precleaning and Sulfur Passivation on the Al2O3/Ge Interface in Ge Metal-Oxide-Semiconductor Capacitors

Surface treatment for Ge substrates using hydrogen chlorine cleaning and chemical passivation are investigated on AuTi/Al2O3/Ge metal-oxide-semiconductor capacitors. After hydrogen chlorine cleaning, a smooth Ge surface almost free from native oxide is demonstrated by atomic force microscopy and x-ray photoelectron spectroscopy observations. Passivation using a hydrogen chlorine solution is found to form a chlorine-terminated surface, while aqueous ammonium sulfide pretreatment results in a surface terminated by Ge-S bonding. Compared with chlorine-passivated samples, the sulfur-passivated ones show less frequency dispersion and better thermal stability based on capacitance-voltage characterizations. The samples with HCl pre-cleaning and (NH4)2S passivation show less frequency dispersion than the HF pre-cleaning and (NH4)2S passivated ones. The surface treatment process using hydrogen chlorine cleaning followed by aqueous ammonium sulfide passivation demonstrates a promising way to improve gate dielectric/Ge interface quality.

Effect of the Si-doped In0.49Ga0.51P barrier layer on the device performance of In0.4Ga0.6As MOSFETs grown on semi-insulating GaAs substrates

In0.4Ga0.6As channel metal?oxide?semiconductor field-effect transistors (MOSFETs) with and without an Si-doped In0.49Ga0.51P barrier layer grown on semi-insulating GaAs substrates have been investigated for the first time. Compared with the In0.4Ga0.6As MOSFETs without an In0.49Ga0.51P barrier layer, In0.4Ga0.6As MOSFETs with an In0.49Ga0.51P barrier layer show higher drive current, higher transconductance, lower gate leakage current, lower subthreshold swing, and higher effective channel mobility. These In0.4Ga0.6As MOSFETs (gate length 2 ?m) with an In0.49Ga0.51P barrier layer exhibit a high drive current of 117 mA/mm, a high transconductance of 71.9 mS/mm, and a maximum effective channel mobility of 1266 cm2/(V?s).

GaSb p-Channel Metal-Oxide-Semiconductor Field-Effect Transistors with Ni/Pt/Au Source/Drain Ohmic Contacts

GaSb is an attractive candidate for future high-performance III–V p-channel metal-oxide-semiconductor-field-effect-transistors (pMOSFETs) because of its high hole mobility. The effect of HCl based-chemical cleaning on removing the non-self limiting and instable native oxide layer of GaSb to obtain a clean and smooth surface has been studied. It is observed that the rms roughness of a GaSb surface is significantly reduced from 2.731 nm to 0.693 nm by using HCl:H2O (1:3) solution. The Ni/Pt/Au ohmic contact exhibits an optimal specific contact resistivity of about 6.89 × 10−7 Ω·cm2 with a 60s rapid thermal anneal (RTA) at 250°C. Based on the chemical cleaning and ohmic contact experimental results, inversion-channel enhancement GaSb pMOSFETs are demonstrated. For a 6 μm gate length GaSb pMOSFET, a maximum drain current of about 4.0 mA/mm, a drain current on-off (ION/IOFF) ratio of > 103, and a subthreshold swing of ~250 mV/decade are achieved. Combined with the split C–V method, a peak hole mobility of about 160 cm2/V·s is obtained for a 24 μm gate length GaSb pMOSFET.

Effect of ultrathin GeOx interfacial layer formed by thermal oxidation on Al2O3 capped Ge

We propose a modified thermal oxidation method in which an Al2O3 capping layer is used as an oxygen blocking layer (OBL) to form an ultrathin GeOx interfacial layer, and obtain a superior Al2O3/GeOx/Ge gate stack. The GeOx interfacial layer is formed in oxidation reaction by oxygen passing through the Al2O3 OBL, in which the Al2O3 layer could restrain the oxygen diffusion and suppress the GeO desorption during thermal treatment. The thickness of the GeOx interfacial layer would dramatically decrease as the thickness of Al2O3 OBL increases, which is beneficial to achieving an ultrathin GeOx interfacial layer to satisfy the demand for small equivalent oxide thickness (EOT). In addition, the thickness of the GeOx interfacial layer has little influence on the passivation effect of the Al2O3/Ge interface. Ge (100) p-channel metal–oxide–semiconductor field-effect transistors (pMOSFETs) using the Al2O3/GeOx/Ge gate stacks exhibit excellent electrical characteristics; that is, a drain current on-off (Ion/Ioff) ratio of above 1×104, a subthreshold slope of ~ 120 mV/dec, and a peak hole mobility of 265 cm2/Vs are achieved.

Solid Phase Reactions of Ni-GaAs Alloys for High Mobility III-V MOSFET Applications

The solid phase reactions of Ni with GaAs substrates are investigated. The experimental results reveal that the Ni-GaAs solid phase reaction forms a ternary phase of Ni2GaAs when annealing temperatures are in the range 250?300?C. As the annealing temperature increases to 400?C, the Ni2GaAs phase starts to decompose due to NiAs phase precipitation. Ni-GaAs alloys processed at 400?C with a 3 min annealing time demonstrate a sheet resistance of 30?/square after unreacted Ni removal in hot diluted-HCl solutions. Therefore, Ni-GaAs alloys formed by solid phase reaction could be promising metallic source/drain structures with significant low series resistance for high mobility III?V metal-oxide-semiconductor field effect transistor (MOSFET) applications.

High-mobility germanium p-MOSFETs by using HCl and (NH4)2S surface passivation

To achieve a high-quality high-κ/Ge interfaces for high hole mobility Ge p-MOSFET applications, a simple chemical cleaning and surface passivation scheme is introduced, and Ge p-MOSFETs with effective channel hole mobility up to 665 cm2/Vs are demonstrated on a Ge (111) substrate. Moreover, a physical model is proposed to explain the dipole layer formation at the metal—oxide—semiconductor (MOS) interface by analyzing the electrical characteristics of HCl- and (NH4)2S-passivated samples.