Search

The second-harmonic generation (SHG) from Si1-xGex alloy films has been investigated by near-infrared femtosecond laser. Recognized by s-out polarized SHG intensity versus rotational angle of sample, the crystal symmetry of the fully strained Si0.83Ge0.17 alloy is found changed from the Oh to the C2 point group due to the inhomogeneity of the strain. Calibrated by double crystal X-ray diffraction, the strain-induced χ(2) is estimated at 5.7 × 10-7 esu. According to the analysis on p-in/s-out SHG, the strain-relaxed Si0.10Ge0.90 alloy film is confirmed to be not fully relaxed, and the remaining strain is quantitatively determined to be around 0.1%.

We report efficient zero-bias high-speed top-illuminated p—i—n photodiodes (PDs) with high responsivity fabricated with germanium (Ge) films grown directly on silicon-on-insulator (SOI) substrates. For a 15 μm-diameter device at room temperature, the dark current density was 44.1 mA/cm2 at −1 V. The responsivity at 1.55 μm was 0.30 A/W at 0 V. The saturation of the optical responsivity at 0 V bias revealed that this photodetector allows a complete photo-generated carrier collection without bias. Although the 3-dB bandwidth of the 15-μm-diameter detector was 18.8 GHz at the reverse bias of 0 V, the detector responsivity was improved by one order of magnitude compared with that reported in the literature. Moreover, the dark current of the detector was significantly reduced. [ABSTRACT FROM AUTHOR]

We describe the structure and testing of one-dimensional array parallel-optics photo-detectors with 16 photodiodes of which each diode operates up to 8 Gb/s. The single element is vertical and top illuminated 30-μm-diameter silicon on insulator (Ge-on-SOI) PIN photodetector. High-quality Ge absorption layer is epitaxially grown on SOI substrate by the ultra-high vacuum chemical vapor deposition (UHV-CVD). The photodiode exhibits a good responsivity of 0.20 A/W at a wavelength of 1550 nm. The dark current is as low as 0.36 μA at a reverse bias of 1 V, and the corresponding current density is about 51 mA/cm2. The detector with a diameter of 30 μm is measured at an incident light of 1.55 μm and 0.5 mW, and the 3-dB bandwidth is 7.39 GHz without bias and 13.9 GHz at a reverse bias of 3 V. The 16 devices show a good consistency. [ABSTRACT FROM AUTHOR]

Efficient coupling from the silicon waveguide to the GeSi layer is the key to success in the GeSi electro-absorption (EA) modulator based on evanescent coupling. A lateral taper in the upper GeSi layer has room for increasing the modulating efficiency and alleviating the sensitivity of the extinction ratio (ER) and insertion loss (IL) to the length of the active region. The light behavior and the effect of the taper are explored in detail using the beam propagation method (BPM). After optimization, the light can nearly be totally confined in the GeSi layer without any oscillation. The modulator with the designed taper can achieve low IL and high ER. [ABSTRACT FROM AUTHOR]

Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 °C for a short period (< 20 s). The films were grown on Si(001) substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged (> 20 s) rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si—Ge mixing at high temperature. [ABSTRACT FROM AUTHOR]

Germanium-tin (Ge1−xSnx) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge0.985Sn0.015 thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge0.985Sn0.015 layer was grown by solid source molecular beam epitaxy. Ge0.985Sn0.015 pMOSFETs with Si surface passivation, TaN/HfO2 gate stack, and nickel stanogermanide [Ni(Ge1−xSnx)] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm2/V·s at an inversion carrier density of 1 × 1013 cm−2. [ABSTRACT FROM AUTHOR]

Uni-traveling-carrier photodiodes (UTC-PDs) with ultrafast response and high saturation output are reported. A gradient doping layer and a narrow InP cliff layer were introduced to enhance the saturation and bandwidth characteristics. We measured the dark current, photo response, bandwidth, and saturation current of the fabricated UTC devices. For a 15-μm-diameter device, the dark current was 3.5 nA at a reverse bias of 1 V, and the 3-dB bandwidth was 17.2 GHz at a reverse bias of 5 V, which are comparable to the theoretically values. The maximum responsivity at 1.55 μm was 0.32 A/W. The saturation output current was over 19.0 mA without bias. [ABSTRACT FROM AUTHOR]

Ge-on-silicon-on-insulator p-i-n photodetectors were fabricated using an ultralow-temperature Ge buffer by ultrahigh-vacuum chemical vapor deposition. For a detector of 70-µm diameter, the 1-dB small-signal compression power was about 110.5 mW. The 3-dB bandwidth at 3-V reverse bias was 13.4 GHz. [ABSTRACT FROM AUTHOR]

Germanium waveguide photodetectors with 4 μm widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 μm. For the 4 × 8 μm2 photodetector, the dark current density is as low as 5 mA/cm2 at −1 V. At a bias of −1 V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at −4 V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm. [ABSTRACT FROM AUTHOR]

Step-coupler waveguide-integrated Ge/Si avalanche photodetector (APD) is based on the vertical multimode interference (MMI), enhancing light scattering towards the Ge active region and creating mirror images of optical modes close to the Ge layer. However, there are two ineluctable contact angels between selectively epitaxial growth Ge and Si layers and selectively epitaxial growth Si and Si substrate, which has an effect on the coupling efficiency and the absorption of the photodetector. Therefore, step-coupled Ge/Si avalanche photodetectors with different step lengths are designed and fabricated. It is found that responsivity of APDs with step-coupler-length of is 0.51 A/W at −6 V, 21% higher than that of , which matches well with simulation absorption. The multiplication gain factor is as high as 50, and the maximum gain-bandwidth product reaches up to 376 GHz. [ABSTRACT FROM AUTHOR]

We report a lateral Ge-on-Si ridge waveguide light emitting diode (LED) grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD). Direct-bandgap electroluminescence (EL) of Ge waveguide under continuous current is observed at room temperature. The heat-enhancing luminescence and thermal radiation-induced superlinear increase of edge output optical power are found. The spontaneous emission and thermal radiation based on the generalized Planck radiation law are calculated and fit very well to the experimental results. The Ge waveguides with different lengths are studied and the shorter one shows stronger EL intensity. [ABSTRACT FROM AUTHOR]

Optical gain characteristics of Ge1−xSnx are simulated systematically. With an injection carrier concentration of 5 × 1018/cm3 at room temperature, the maximal optical gain of Ge0.922Sn0.078 alloy (with n-type doping concentration being 5 × 1018/cm3) reaches 500 cm−1. Moreover, considering the free-carrier absorption effect, we find that there is an optimal injection carrier density to achieve a maximal net optical gain. A double heterostructure Ge0.554Si0.289Sn0.157/Ge0.922Sn0.078/Ge0.554Si0.289Sn0.157 short-wave infrared laser diode is designed to achieve a high injection efficiency and low threshold current density. The simulation values of the device threshold current density Jth are 6.47 kA/cm2 (temperature: 200 K, and λ = 2050 nm), 10.75 kA/cm2 (temperature: 200 K, and λ = 2000 nm), and 23.12 kA/cm2 (temperature: 300 K, and λ = 2100 nm), respectively. The results indicate the possibility to obtain a Si-based short-wave infrared Ge1−xSnx laser. [ABSTRACT FROM AUTHOR]