Kah-Wee Ang

Silicon Modulators and Germanium Photodetectors on SOI: Monolithic Integration, Compatibility, and Performance Optimization

Si modulators and Ge photodetectors are monolithically integrated on Si-on-insulator. The carrier-depletion-type Si modulators achieved high modulation efficiency and speed (<i>V</i> _¿ <i>L</i> _¿ = 2.56 V·cm, 10 Gb/s). Low-voltage operation (<i>V</i> _RF = 1 <i>V</i> _pp) was also demonstrated. Introducing a low-thermal-budget postepitaxy anneal improves the performance of the Ge photodetectors, thus resulting in significantly improved dark current. The responsivity and speed in the low-voltage regime are also enhanced, which enhances low-voltage or even short-circuit (<i>V</i> _Bias = 0 V) operation.

Monolithic Polarization and Phase Diversity Coherent Receiver in Silicon

In this paper, we realized a monolithic silicon photonic integrated circuit (PIC) for polarization and phase diversity coherent detection. The PIC includes two polarization beam splitters, two 90° optical hybrids, and four pairs of balanced photodiodes implemented as integrated germanium detectors. We tested the PIC using polarization-division multiplexed quadrature phase-shift keyed signals at 43 and at 112 Gb/s.

Lattice strain analysis of transistor structures with silicon–germanium and silicon–carbon source∕drain stressors

We report the characterization of strain components in transistor structures with silicon–germanium (Si0.75Ge0.25) and silicon–carbon (Si0.99C0.01) stressors grown by selective epitaxy in the source and drain regions. The spacing between the source and drain stressors is 35nm. Lattice strain analysis was performed using high-resolution transmission electron microscopy (HRTEM) and diffractograms obtained by fast Fourier transform of HRTEM images. The lateral strain component exx and the vertical strain component ezz were derived from the (220) and (002) reflections in the diffractogram, respectively. SiGe source and drain stressors lead to lateral compressive strain and vertical tensile strain in the Si channel. On the other hand, the SiC source and drain stressors give rise to lateral tensile strain and vertical compressive strain in the Si channel, an effect complementary to that of SiGe source∕drain stressors. The results of this work will be useful for channel strain engineering in complementary metal-...

Split Bull's eye shaped aluminum antenna for plasmon-enhanced nanometer scale germanium photodetector.

Bulls eye antennas are capable of efficiently collecting and concentrating optical signals into an ultrasmall area, offering an excellent solution to break the bottleneck between speed and photoresponse in subwavelength photodetectors. Here, we exploit the idea of split bulls eye antenna for a nanometer germanium photodetector operating at a standard communication wavelength of 1310 nm. The nontraditional plasmonic metal aluminum has been implemented in the resonant antenna structure fabricated by standard complementary metal-oxide-semiconductor (CMOS) processing. A significant enhancement in photoresponse could be achieved over the conventional bulls eye scheme due to an increased optical near-field in the active region. Moreover, with this novel antenna design the effective grating area could be significantly reduced without sacrificing device performance. This work paves the way for the future development of low-cost, high-density, and high-speed CMOS-compatible germanium-based optoelectronic devices.

Low Thermal Budget Monolithic Integration of Evanescent-Coupled Ge-on-SOI Photodetector on Si CMOS Platform

The design and fabrication of a monolithically integrated evanescent-coupled Ge-on-silicon-on-insulator (SOI) photodetector and CMOS circuits were realized on common SOI platform using an ¿electronic-first and photonic-last¿ integration approach. High-performance detector with an integrated Si waveguide was demonstrated on epitaxial Ge-absorbing layer selectively grown on an ultrathin SOI substrate. Performance metrics of photodetector designs featuring vertical and lateral PIN configurations were investigated. When operated at a bias of -1.0 V, a vertical PIN detector achieved a lower I dark of ~ 0.57 ¿A as compared to a lateral PIN detector, a value that is below the typical ~ 1 ¿A upper limit acceptable for high-speed-receiver design. Very high responsivity of ~ 0.92 A/W was obtained in both detector designs for a wavelength of 1550 nm, which corresponds to a quantum efficiency of ~ 73%. Impulse response measurements showed that the vertical PIN detector gives rise to a smaller full-width at half-maximum of ~ 24.4 ps over a lateral PIN detector, which corresponds to a -3 dB bandwidth of ~ 11.3 GHz. RC time delay is shown to be the dominant factor limiting the speed performance. Eye patterns (pseudorandom binary sequence 27-1) measurement further confirms the achievement of high-speed and low-noise photodetection at a bit rate of 8.5 Gb/s. Excellent transfer and output characteristics have also been achieved by the integrated CMOS inverter circuits in addition to the well-behaved logic functions. The introduction of an additional thermal budget (800°C) arising from the Ge epitaxy growth has no observable detrimental impact on the short-channel control of the CMOS inverter circuit. In addition, we describe the issues associated with monolithic integration and discuss the potential of Ge-detector/Si CMOS receiver for future optical communication applications.

n-MOSFET With Silicon–Carbon Source/Drain for Enhancement of Carrier Transport

A novel strained-silicon (Si) n-MOSFET with 50-nm gate length is reported. The strained n-MOSFET features silicon-carbon (Si_1-yC_y) source and drain (S/D) regions formed by a Si recess etch and a selective epitaxy of Si_1-yC_y in the S/D regions. The carbon mole fraction incorporated is 0.013. Lattice mismatch of ~0.56% between Si _0.987C_0.013 and Si results in lateral tensile strain and vertical compressive strain in the Si channel region, both contributing to substantial electron-mobility enhancement. The conduction-band offset DeltaE_c between the Si_0.987C_0.013 source and the strained Si channel could also contribute to an increased electron injection velocity nu_inj from the source. Implementation of the Si_0.987C_0.013 S/D regions for n-MOSFET provides significant drive current I_Dsat enhancement of up to 50% at a gate length of 50 nm

Novel Silicon-Carbon (Si:C) Schottky Barrier Enhancement Layer for Dark-Current Suppression in Ge-on-SOI MSM Photodetectors

This letter reports the first demonstration of an evanescent coupled germanium-on-silicon-on-insulator (Ge-on-SOI) metal-semiconductor-metal (MSM) photodetector with a novel silicon-carbon (Si:C) Schottky barrier enhancement layer. Through the insertion of a Si:C barrier layer between the metal/Ge interface, the hole Schottky barrier height phibh can effectively be enhanced to ~0.52 eV above the valence band edge. As a result, significant dark-current IDark suppression by more than four orders of magnitude was demonstrated, leading to an impressive IDark of ~11.5 nA for an applied bias VA of 1.0 V. Optical measurements performed at a photon wavelength of 1550 nm revealed the achievement of good internal responsivity and quantum efficiency of ~530 mA/W and 42.4%, respectively, making such a high-performance Ge-on-SOI MSM photodetector a promising option for optical communication applications.

Nickel-Silicide:Carbon Contact Technology for N-Channel MOSFETs With Silicon–Carbon Source/Drain

To explore the potential of nickel-silicide:carbon (NiSi:C) as contact technology for MOSFETs with silicon-carbon (Si:C) source/drain (S/D) regions, we examined the effects of incorporating 1.0 at.% of carbon in Si prior to nickel silicidation. The addition of carbon was found to improve the morphological and phase stability of NiSi:C contacts. This is possibly due to the presence of carbon at the NiSi:C grain boundaries and NiSi:C/Si interface, which will modify the grain-boundary and interfacial energies. This will influence the kinetics of NiSi:C silicidation. In this letter, we have also demonstrated the first integration of NiSi:C contacts in MOSFETs with Si:C S/D regions. We further show that NiSi:C silicidation suppresses the formation of active deep-level defects, leading to superior n+/p junction characteristics.

Thin body silicon-on-insulator N-MOSFET with silicon-carbon source/drain regions for performance enhancement

We report a novel strained n-channel transistor structure featuring silicon-carbon (SiC) source and drain (S/D) regions formed on thin body SOI substrate. The SiC material is pseudomorphically grown by selective epitaxy and the carbon mole fraction incorporated is 1%. Lattice mismatch between SiC and Si results in uniaxial tensile strain in the Si channel region which contributes favorably to electron mobility enhancement. Drive current IDsat enhancement of 25% was observed for 90 nm gate length LG transistors, and IDsat enhancement of up to 35% was observed at LG of 70 nm. In addition, drive current enhancement shows dependence on device width and channel orientation. All transistors were formed on (001) SOI substrates. The largest IDsat enhancement is observed for transistors with the [010] channel orientation

Low-Voltage and High-Responsivity Germanium Bipolar Phototransistor for Optical Detections in the Near-Infrared Regime

Germanium (Ge) bipolar phototransistors with high-responsivity performance are demonstrated using a low-temperature selective Ge epitaxy process. Large photocurrent and optical response enhancement are achieved over a conventional p-i-n Ge photodetector, which is predominantly attributed to the current gain induced by transistor actions. When illuminated with a photon wavelength of 1.55 mum , a Ge phototransistor shows a large responsivity of ~ 2.0 A/W for a low operating bias VA of 1.0 V. Optical measurement results further show that good photoresponse could be achieved for a spectral range of 1.31-1.62 mum, making such a device a very promising option for optical detections in the near-infrared (including L -band) wavelength regime.