Buwen Cheng

GeSn p-i-n photodetector for all telecommunication bands detection

Using a 820 nm-thick high-quality Ge0.97Sn0.03 alloy film grown on Si(001) by molecular beam epitaxy, GeSn p-i-n photodectectors have been fabricated. The detectors have relatively high responsivities, such as 0.52 A/W, 0.23 A/W, and 0.12 A/W at 1310 nm, 1540 nm, and 1640 nm, respectively, under a 1 V reverse bias. With a broad detection spectrum (800-1800 nm) covering the whole telecommunication windows and compatibility with conventional complementary metal-oxide-semiconductors (CMOS) technology, the GeSn devices are attractive for applications in both optical communications and optical interconnects.

Germanium–Tin (GeSn) p-Channel MOSFETs Fabricated on (100) and (111) Surface Orientations With Sub-400

In this letter, we report the first study of the dependence of carrier mobility and drive current I_Dsat of Ge_0.958Sn_0.042 p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) on surface orientations. Compressively strained Ge_0.958Sn_0.042 channels were grown on (100) and (111) Ge substrates. Sub-400°C Si₂H₆ treatment was introduced for the passivation of the GeSn surface prior to gate stack formation. Source/ drain series resistance and subthreshold swing S were found to be independent of surface orientation. The smallest reported S of 130 mV/decade for GeSn pMOSFETs is achieved. The (111)-oriented device demonstrates 13% higher IDsat over the (100)oriented one at a V_GS-V_TH of -0.6 V and V_DS of -0.9 V. We also found that GeSn pMOSFETs with (111) surface orientation show 18% higher hole mobility than GeSn pMOSFETs with (100) orientation.

^{\circ}\hbox{C}\ \hbox{Si}_{2}\hbox{H}_{6}

We report the first demonstration of GeSn pMOSFETs. Key highlights of this work also includes a 180 °C GeSn MBE growth, sub-370 °C Si<inf>2</inf>H<inf>6</inf> surface passivation and gate stack process for GeSn, and an implantless metallic NiGeSn S/D formed at 350 °C. A hole mobility of 430 cm²/Vs is obtained for GeSn pMOSFETs, which is 66% higher than that of the Ge control pMOSFETs. GeSn pMOSFETs show a 64% lower S/D resistance as compared to the Ge control devices.

Passivation

Surface-illuminated GeSn p-i-n photodetectors (PDs) with Ge0.964Sn0.036 active layer on Ge substrate were fabricated. Photodetection up to 1.95 μm is achieved with a responsivity of 0.13 A/W. High responsivities of 0.56 and 0.71 A/W were achieved under a reverse bias voltage of 3 V at 1640 and 1790 nm, respectively. A low dark current of 1.08 μA was obtained at a reverse bias of 1 V with a diameter of 150 μm, which corresponds to a current density of 6.1 mA/cm2. This value is among the lowest dark current densities reported among GeSn PDs.

High-mobility germanium-tin (GeSn) P-channel MOSFETs featuring metallic source/drain and sub-370 °C process modules

A Ge/Si heterojunction light emitting diode with a p(+)-Ge/i-Ge/N+-Si structure was fabricated using the ultrahigh vacuum chemical vapor deposition technology on N+-Si substrate. The device had a good I-V rectifying behavior. Under forward bias voltage ranging from 1.1 to 2.5 V, electroluminescence around 1565 nm was observed at room temperature. The mechanism of the light emission is discussed by the radiative lifetime and the scattering rate. The results indicate that germanium is a potential candidate for silicon-based light source material

High-responsivity GeSn short-wave infrared p-i-n photodetectors

In this work, we report the first demonstration of GeSn pTFET. Good device characteristics were obtained. This may be attributed to direct BTBT, high hole mobility in the GeSn channel, and the formation of abruptly and heavily doped N+ source. The ION performance can be improved with further device optimization.

Electroluminescence from Ge on Si substrate at room temperature

National Basic Research Program of China [2007CB613404]; National Natural Science Foundation of China [60676027, 50672079]; Key Projects of Fujian Science and Technology [2006H0036]; Program for New Century Excellent Talents in University

Towards direct band-to-band tunneling in P-channel tunneling field effect transistor (TFET): Technology enablement by Germanium-tin (GeSn)

A compact two-mode (de)multiplexer [(DE)MUX] based on symmetric Y-junction and multimode interference (MMI) waveguides was designed by 3D beam propagation method (BPM). The phase evolution in the structure was discussed in detail. Simulations show that the optical bandwidth is as large as 100 nm (1500 nm ~1600 nm). The two-mode (DE)MUX is very compact compared with the other kind of mode (DE)MUX. The length of the structure is only 48.8 μm. Simulation also shows the fabrication tolerance is as large as ± 75 nm.

Room temperature photoluminescence of tensile-strained Ge/Si0.13Ge0.87 quantum wells grown on silicon-based germanium virtual substrate

Ultrathin GeSn channels were epitaxially grown on Si(111) and (001) substrates using solid source molecular beam epitaxy. Well-behaved GeSn quantum well (QW) pTFETs and pMOSFETs were fabricated on Si. GeSn QW pMOSFETs on Si(111) demonstrate a high effective hole mobility of 505 cm2/Vs, indicating the high crystallinity of the GeSn material. GeSn QW pTFETs on Si(111) outperform the devices on Si(001) on subthreshold swing (SS) and ON-state current ION. (111)-oriented GeSn pTFET with a 4-nm-thick channel achieves a steep SS of ~60 mV/decade and a high ON-state/OFF-state current ratio of 107, which are superior to those of the other reported non-Si pTFETs with a small bandgap.

Compact two-mode (de)multiplexer based on symmetric Y-junction and multimode interference waveguides.

In this paper, we report the worlds first germanium-tin (GeSn) channel nMOSFETs. Highlights of process module advances are: low temperature (400 °C) process for forming high quality n+/p junction with high dopant activation and reduced dopant diffusion; interface engineering achieved with GeSnO2 interfacial layer (IL) between high-k gate dielectric and GeSn channel. A gate-last process was employed. The GeSn nMOSFET with GeSnO2 IL demonstrates a substantially improved SS in comparison with Ge control, and an ION/IOFF ratio of 104.