Chang Hudong

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.

MIM capacitors with various Al2O3 thicknesses for GaAs RFIC application

The impact of various thicknesses of Al2O3 metal—insulator—metal (MIM) capacitors on direct current and radio frequency (RF) characteristics is investigated. For 20 nm Al2O3, the fabricated capacitor exhibits a high capacitance density of 3850 pF/mm2 and acceptable voltage coefficients of capacitance of 681 ppm/V2 at 1 MHz. An outstanding VCC-α of 74 ppm/V2 at 1 MHz, resonance frequency of 8.2 GHz and Q factor of 41 at 2 GHz are obtained by 100 nm Al2O3 MIM capacitors. High-performance MIM capacitors using GaAs process and atomic layer deposition Al2O3 could be very promising candidates for GaAs RFIC applications.

Ultra high-speed InP/InGaAs SHBTs with/t and/max of 185 GHz

An InP/InGaAs single heterojunction bipolar transistor (SHBT) with high maximum oscillation frequency (fmax) and high cutoff frequency (ft) is reported. Efforts have been made to maximize fmax and ft simultaneously including optimizing the epitaxial structure, base-collector mesa over-etching and base surface preparation. The measured ft and fmax both reached 185 GHz with an emitter size of 1 × 20 μm2, which is the highest fmax for SHBTs in mainland China. The device is suitable for ultra-high speed digital circuits and low power analog applications.

The Microwave Characteristics of an In0.4Ga0.6As Metal-Oxide-Semiconductor Field-Effect Transistor with an In0.49Ga0.51P Interfacial Layer

A high microwave performance enhancement-mode (E-mode) In0.4Ga0.6As channel metal-oxide-semiconductor field-effect transistor (MOSFET) with a Si-doped In0.49gGa0.51P interfacial layer is fabricated. A 0.8-μm-gate-length In0.4Ga0.6As MOSFET with a 5-nm Al2O3 dielectric layer provides a current gain cutoff frequency of 16.7 GHz and a maximum oscillation frequency of 52 GHz. A semi-empirical small-signal-parameter extraction technique accounting for the low frequency anomaly of this MOSFET device is described, which is based on on-wafer S-parameter measurements. Excellent agreement between measured and simulated scattering parameters as well as the physically realistic circuit elements demonstrates the validity of this approach.

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.

Extrinsic Base Surface Passivation in High Speed “Type-II" GaAsSb/InP DHBTs Using an InGaAsP Ledge Structure

Type-II GaAsSb/InP DHBTs with selectively-etched InGaAsP ledge structures are fabricated and characterized for the first time. The novel InGaAsP/GaAsSb/InP DHBTs with a 20 nm lattice-matched GaAsSb base and a 75 nm InP collector have a dc current gain improvement by a factor of 2 and a cutoff frequency fT of 190 GHz. The InGaAsP ledge design provides a simple but effective approach to suppress the extrinsic base surface recombination and enable GaAsSb/InP DHBTs to further increase the operating frequencies and integration levels for millimeter wave 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.

High-Quality Single Crystalline Ge(111) Growth on Si(111) Substrates by Solid Phase Epitaxy

Heterogeneous integration of crystalline Ge layers on cleaned and H-terminated Si(111) substrates are demonstrated by employing a combination of e-beam evaporation and solid phase epitaxy techniques. High-quality single crystalline Ge(111) layers on Si(111) substrates with a smooth Ge surface and an abrupt interface between Ge and Si are obtained. An XRD rocking curve scan of the Ge(111) diffraction peak shows a FWHM of only 260 arcsec for a 50-nm-thick Ge layer annealed at 600°C with a ramp-up rate of 20°C/s and a holding time of 1 min. The AFM images exhibit that the rms surface roughness of all the crystalline Ge layers are less than 2.1 nm.