Chunlai Xue

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}

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.

Passivation

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

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.

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

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.

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

We report a novel common gate-stack solution for In_0.7Ga_0.3As n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) and Ge_0.97Sn_0.03 p-channel metaloxide-semiconductor field-effect transistors (pMOSFETs), featuring sub-400 °C Si₂H₆ passivation, sub-1.75-nm capacitance equivalent thickness (CET), and single TaN metal gate. By incorporating Si₂H₆ passivation, an ultrathin SiO₂/Si interfacial layer is formed between the high-k gate dielectric and the high mobility InGaAs and GeSn channels. The In_0.7Ga_0.3As nMOSFET and Ge_0.97Sn_0.03 pMOSFET show drive currents of ~143 and ~69μA/μm, respectively, at |V_DS| and |V_GS - V_TH| of 1V for a gate length L_G of 4 μm. At an inversion carrier density N_inv of 10¹³ cm^-2, In_0.7Ga_0.3As nMOSFETs and Ge_0.97Sn_0.03 pMOSFETs show electron and hole mobilities of ~495 and ~230cm²/V·s, respectively. At N_inv of 4 × 10¹² cm^-2, electron and hole mobility values of ~705 and ~ 346cm²/V·s are achieved. Symmetric V_TH is realized by choosing a metal gate with midgap work function, and CET of less than 1.75nm is demonstrated with a gate-leakage current density (JG) of less than 10^-4A/cm² at a gate bias of V_TH ± 1V. Using this gate-stack, a Ge_0.95Sn_0.05 pMOSFET with the shortest L_G of 200nm is also realized. Drive current of ~680μA/μm is achieved at V_DS of -1.5V and V_GS - V_TH of -2V, with peak intrinsic transconductance G_m,int of ~492μS/μm at V_DS of -1.1V.

Strained germanium-tin (GeSn) N-channel MOSFETs featuring low temperature N+/P junction formation and GeSnO2 interfacial layer

The enhanced room-temperature photoluminescence of porous Si nanowire arrays and its mechanism are investigated. Over 4 orders of magnitude enhancement of light intensity is observed by tuning their nanostructures and surface modification. It is concluded that the localized states related to Si-O bonds and self-trapped excitations in the nanoporous structures are attributed to the strong light emission.

Sub-400 degrees C Si2H6 Passivation, HfO2 Gate Dielectric, and Single TaN Metal Gate: A Common Gate Stack Technology for In0.7Ga0.3As and Ge1-xSnx CMOS

In this paper, we report efficient high-speed top-illuminated p-i-n photodiodes with high responsivity fabricated from germanium (Ge) films grown directly on silicon-on-insulator substrates. The devices were characterized with respect to their dark current, responsivity, and 3-dB bandwidth (BW) in the near infrared. For a 20-μm-diameter device at room temperature, the dark current densities were approximately 38.3 mA/cm2 at -1 V. The responsivity (\mmb R) at 1.55 μm was 0.30 A/W, corresponding to a quantum efficiency of 24%. The 3-dB BW of the detector with 20-μm diameter is as high as 23.3 GHz.