X. Z. Chen

Aligned carbon nanotubes for through-wafer interconnects

Through-wafer interconnects by aligned carbon nanotube for three-dimensional stack integrated chip packaging applications have been reported in this letter. Two silicon wafers are bonded together by tetra-ethyl-ortho-silicate. The top wafer (100μm thick) with patterned through-holes allows carbon nanotubes to grow vertically from the catalyst layer (Fe) on the bottom wafer. By using thermal chemical vapor deposition technique, the authors have demonstrated the capability of growing aligned carbon nanotube bundles with an average length of 140μm and a diameter of 30μm from the through holes. The resistivity of the bundles is measured to be 0.0097Ωcm by using a nanomanipulator.

InSbN alloys prepared by two-step ion implantation for infrared photodetection

InSbN alloys are fabricated by two-step nitrogen ion implantation into InSb (111) wafers. X-ray photoelectron spectroscopy indicates that most of the implanted nitrogen ions substitute Sb to form In–N bonds. The percentage of the In–N bonds is found to decrease with the increase in the implanted nitrogen. Such alloys can effectively detect long wavelength infrared radiation and the absorption peak energies can be controlled by monitoring the implanted nitrogen dose. The measured peak wavelengths are consistent with the band gaps of the alloys calculated using a ten-band k⋅p model.

Bonding and diffusion of nitrogen in the InSbN alloys fabricated by two-step ion implantation

We report bonding and diffusion behavior of nitrogen incorporated into InSb wafer by two-step implantation. Three nitrogen-containing regions, i.e., a surface accumulation region, a uniform region, and a tail region, were observed in the samples after post annealing. X-ray photoelectron spectroscopy measurements at different depths reveal that majority of the nitrogen forms In-N bonds in the uniform region but exists as interstitial defects in the tail region. The diffusion coefficients of nitrogen in InSb were obtained by fitting the modified Fick’s law with experimental data and the activation energy of 0.55 ± 0.04 eV extracted confirms the interstitial dominating diffusion of nitrogen in the InSb wafer.

Anisotropy induced large exchange bias behavior in ball milled Ni–Co–Mn–Sb alloys

We report the effect of decrease in the grain size on the structural, magnetic and exchange bias (EB) behavior in ball milled Ni50−xCoxMn38Sb12 (x=0 and 5) Heusler alloys. The existence of a wide range of grain sizes in the ball milled samples results in dramatic changes in the structural and magnetic properties. For x=0, a large EB field of 3.2 kOe is observed in the ball milled sample, compared to a value of 245 Oe of the bulk sample. This increase is attributed to the enhanced exchange coupling between the soft and hard magnetic particles.We report the effect of decrease in the grain size on the structural, magnetic and exchange bias (EB) behavior in ball milled Ni50−xCoxMn38Sb12 (x=0 and 5) Heusler alloys. The existence of a wide range of grain sizes in the ball milled samples results in dramatic changes in the structural and magnetic properties. For x=0, a large EB field of 3.2 kOe is observed in the ball milled sample, compared to a value of 245 Oe of the bulk sample. This increase is attributed to the enhanced exchange coupling between the soft and hard magnetic particles.

Biosensors based on flexural mode piezo-diaphragm

This paper presents a mass sensitive biosensor utilizing a flexural vibration mode of a micromachined piezoelectric micro-diaphragm. The mass sensitivity of the diaphragm has been investigated with respect to the vibration modes. Theoretical analysis reveals that, for the same multilayer structure, the mass sensitivity is mainly determined by the mass per unit area of the diaphragm, the flexural mode sensor can work at a lower operating frequency than thickness mode without losing its mass sensitivity-about 30 times higher than that of a QCM. A biosensor with Q value of more than 200 has been demonstrated at a resonant frequency of as low as 120 kHz. Frequency shift in response to captured goat IgG on sensor surface has been detected. These results indicate that the flexural mode micromachined diaphragm has a potential to be an alternative to the low-cost QCM biosensors.

Narrow Band Gap InSbN Films Fabricated by Two-Step Ion-Implantation for Long Wavelength Infrared Photodetection

We report InSbN films prepared by two-step nitrogen ion implantation into InSb wafers. It is found that films of over 400 nm with nearly uniform nitrogen distribution can be formed and most of the implanted nitrogen ions can form In-N bonds, resulting in band gap bowing and reduction of carrier concentration. It is also found that such films can detect long wavelength infrared radiation and the absorption peak energies can be controlled by monitoring the implanted nitrogen dose. The measured peak wavelengths are consistent with the band gaps of the alloys calculated using a 10-band kp model.

Electrical & optical properties of Mg-doped narrow band-gap InSbN p-n junction

InSbN p-n junctions are fabricated by direct implantation of N+ and Mg+ into InSb wafers and their electrical and optical properties are characterized. It is found that high quality p-n junctions can be formed and they can absorb photons to form photocurrent. Furthermore, the peak and cut-off wavelengths absorbed can be controlled by monitoring the incorporated nitrogen and the measured peak wavelengths are consistent with the band gaps of the alloys calculated using a 10-band k·p model based on In-N bond.

Properties of InSb (N) epilayers grown by metal-organic chemical vapor deposition

High quality InSb and InSbN alloys were grown epitaxially on InSb (100) by metal-organic chemical vapor deposition. Low temperature photoluminescence spectra of InSb epilayers revealed that in addition to the main band-to-band emission around 5.4 μm, an emission peak around 5.87 μm was also be observed. Our results indicate that the low energy emission peak was originated from the antisite SbIn defects. Discrepancy of diffraction peak position between InSbN alloy and InSb epilayers was detected from the XRD measurement, indicating that the nitrogen has been incorporated into InSb. Photoluminescence measurement showed that the band gap of the InSbN alloy has been extended to longer wavelength by the N incorporation. Band-gap narrowing effect from the high carrier concentration has been taken into consideration to explain the difference between the band gap values from photoluminescence and photo current measurement.

Study of annealing condition of InSbN alloys fabricated by ion implantation

InSbN alloys are the new narrow bandgap semiconductors capable of broadband and long wavelength infrared photodetection. This paper reports the annealing conditions on the properties and quality of InSbN alloys, fabricated by multi-step ion implantation. The InSbN samples were annealed at different annealing methods, temperatures, and periods of time. They were characterized by various techniques, such as x-ray photoelectron spectroscopy and x-ray diffraction. It is found that the low-temperature-long-time annealing was better for defects elimination, while high-temperature-short-time annealing made more nitrogen activated. With the experimental data, detailed bonding of nitrogen in the alloys and their effects on the quality and properties can be achieved.

INSBN Junction Diode Fabricated by Ion Implantation

InSbN photodiodes prepared by N+ and Mg+ implantation into InSb wafers for long wavelength infrared photodetection are demonstrated for the first time. The detection wavelength can be controlled by monitoring the implanted nitrogen. Such devices are capable of mid- and long-wavelength infrared photodetection and potential candidates for terahertz radiation.