Hyperdoped Si materials extend Si response range into near infrared by forming intermediate band in Si band gap. Ti hyperdoped Si (Si:Ti) has been demonstrated to have subbandgap photo response. In this work, we fabricated and characterized Si:Ti photodiodes and optimized the structure. At room temperature, the 3.5×10-3 EQE has been obtained at telecommunication wavelength 1550nm. And the detectable response extends until 2250nm. The results show the potential of Si:Ti materials being both Si:Ti photovoltaics and commercialized IR detection. To improve the efficiency of Si:Ti photodetectors, the affection of absorption rate, devices structure and the Si:Ti crystal quality is discussed.
The application of silicon photonic technologies to optical telecommunications requires the development of
near-infrared detectors monolithically integrated to the Si platform. Recently, efforts in this area have focused on
developing detectors from pure-Ge grown epitaxially on Si substrates. Much effort has been spent on achieving growth
of high quality, relaxed Ge films for device structures, but low temperature growth and processing compatible with
complementary-metal-oxide-semiconductor (CMOS) technology has yet to be achieved. In this paper, we report on p-i-n
heterostructure photodiodes fabricated from Ge films grown directly on Si substrates using a low temperature chemical
vapor deposition (CVD) process.
The heterostructures were grown on arsenic-doped (n-type) Si(100) with resistivity 0.003 Ω-cm. A 350nm
thick layer of intrinsic Ge was deposited first as the active region, followed by 100nm of boron-doped (p-type) Ge.
Ohmic contacts were formed by evaporation of Cr and Au. The diodes were characterized with respect to their dark
currents and responsivities in the near-IR. For a 60-μm-diameter device at room temperature, the dark current densities
were on the order of 10-2 A/cm2 and 103 A/cm2 at -1V and 1V, respectively, the "turn-on" voltage was found to be 0.26
V, and the ideality factor n was found to be 1.2. The external quantum efficiency of the devices was measured at room
temperature over the range 1-1.8 μm. The responsivities at 1.3 and 1.55 μm were found to be 0.26 and 0.11,
respectively.
We report the design and fabrication of a micromachined quartz crystal balance (QCM) array for self
assembled monolayers (SAMs) and protein adsorption studies. The microQCM was fabricated using recently
developed inductively coupled plasma etching process for quartz to realize resonators with 60 &mgr;m thickness
and electrode diameters of 0.5 mm. The reduction in the thickness and lateral pixel size has resulted in a
sensitivity improvement by factor of 1700 over a commercially available macro-sized QCM. Adsorption of
hexadecanethiol on the gold electrode of the QCM in ethanol at a concentration of 1 mM was recorded in real
time and a frequency shift of 3650 Hz was obtained. Modeling the SAMs layer as an ideal, rigid mass layer
the expected frequency shift was calculated to be 1031 Hz. This was followed by a study of the adsorption of
human serum albumin (HSA) protein on the SAMs layer. For 1.5×10-10 moles/ml concentration of protein
solution in phosphate buffer solution (PBS) we obtained a frequency change of 13.28 kHz. Modeling the
protein layer as a viscoelastic layer in a viscous Newtonian fluid, for saturation protein surface coverage, the
frequency change was calculated to be 17.27 kHz whereas the experimentally obtained frequency change was
51.82 kHz. In both rigid and viscoelastic film adsorption experiments, we find the microQCM to exhibit three
times greater sensitivity than the predicted value when operated at the third overtone. These results show that
the micromachined QCM in array format is a very sensitive gravimetric sensor capable of mass resolutions
into the femtograms range.
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