Design requirements for group-IV laser based on fully strained Ge1-xSnx embedded in partially relaxed Si1-y-zGeySnz buffer layers

Theoretical calculation using the model solid theory is performed to design the stack of a group-IV laser based on a fully strained Ge1-xSnx active layer grown on a strain relaxed Si1-y-zGeySnz buffer/barrier layer. The degree of strain relaxation is taken into account for the calculation for the first time. The transition between the indirect and the direct band material for the active Ge1-xSnx layer is calculated as function of Sn content and strain. The required Sn content in the buffer layer needed to apply the required strain in the active layer in order to obtain a direct bandgap material is calculated. Besides, the band offset between the (partly) strain relaxed Si1-y-zGeySnz buffer layer and the Ge1-xSnx pseudomorphically grown on it is calculated. We conclude that an 80% relaxed buffer layer needs to contain 13.8% Si and 14% Sn in order to provide sufficiently high band offsets with respect to the active Ge1-xSnx layer which contains at least 6% Sn in order to obtain a direct bandgap

High-resolution imaging of kidney vascular corrosion casts with nano-CT

A vascular corrosion cast of an entire mouse kidney was scanned with a modular multiresolution X-ray nanotomography system. Using an isotropic voxel pitch of 0.5 mu m, capillary systems such as the vasa recta, peritubular capillaries and glomeruli were clearly resolved. This represents a considerable improvement over corrosion casts scanned with microcomputed tomography systems. The resolving power of this system was clearly demonstrated by the unique observation of a dense, subcapsular mat of capillaries enveloping the entire outer surface of the cortical region. Resolution of glomerular capillaries was comparable to similar models derived from laser scanning confocal microscopy. The high-resolution, large field of view and the three-dimensional nature of the resulting data opens new possibilities for the use of corrosion casting in research

Germanium-on-silicon planar concave grating wavelength (de)multiplexers in the mid-infrared

Mid-infrared wavelength (de)multiplexers based on planar concave gratings (PCGs) fabricated on a germanium-on-silicon waveguide platform are presented. PCGs with two different types of gratings (flat facet and distributed bragg reflectors) are analyzed for both transverse electric (TE) and transverse magnetic (TM) polarizations. The insertion loss and cross talk for flat facet PCGs are found to be -7.6/-6.4¿dB and 27/21¿dB for TE/TM polarization. For distributed bragg reflector PCGs the insertion loss and cross talk are found to be -4.9/-4.2¿dB and 22/23¿dB for TE/TM polarization

Germanium-on-silicon mid-infrared arrayed waveguide grating multiplexers

In this letter, we describe the use of a germanium-on- silicon waveguide platform to realize an arrayed waveguide grating (AWG) operating in the 5 mu m wavelength range, which can be used as a wavelength multiplexer for mid-infrared (midIR) light engines or as the core element of a midIR spectrometer. Ge-on-Si waveguide losses in the range 2.5-3.5 dB/cm for TE polarized light and 3-4 dB/cm for TM polarized light in the 5.15-5.4 mu m wavelength range are reported. A 200 GHz channel spacing 5-channel AWG with an insertion loss/crosstalk of 2.5/3.1 dB and 20/16 dB for TE and TM polarization, respectively, is demonstrated

A demonstration of donor passivation through direct formation of V-As-i complexes in As-doped Ge1-xSnx

Positron annihilation spectroscopy in the Doppler and coincidence Doppler mode was applied on Ge1 xSnx epitaxial layers, grown by chemical vapor deposition with different total As concentrations (1019-1021 cm3), high active As concentrations (1019 cm3), and similar Sn concentrations (5.9%-6.4%). Positron traps are identified as mono-vacancy complexes. Vacancy-As complexes, V-Asi, formed during the growth were studied to deepen the understanding of the electrical passivation of the Ge1 xSnx:As epilayers. Larger monovacancy complexes, V-Asi (i 2), are formed as the As doping increases. The total As concentration shows a significant impact on the saturation of the number of As atoms (i 1/4 4) around the vacancies in the sample epilayers. The presence of V-Asi complexes decreases the dopant activation in the Ge1 xSnx:As epilayers. Furthermore, the presence of Sn failed to hinder the formation of larger V-Asi complexes and thus failed to reduce the donor-deactivation.Peer reviewe

Low-temperature epitaxy of highly-doped n-type Si at high growth rate by chemical vapor deposition for bipolar transistor application

peer reviewedWe investigated the growth of in-situ n-type doped epitaxial Si layers with arsenic and phosphorus by means of low-temperature chemical vapor deposition using trisilane as Si-precursor. Indeed, in order to prevent the alteration of the characteristics of the devices which are already present on the wafer, an epitaxy process at low temperature is highly desired for applications such as BiCMOS. In this work, the varying parameters are the deposition temperature, the Si-precursor mass flow and the dopant gas flow. As a result, a process for the deposition of heavily doped epilayers was demonstrated at 600 °C with high deposition rate, which is important for maintaining high throughput and low process cost. We showed that using trisilane as a Si-precursor resulted in a much more linear n-type doping behavior than using dichlorosilane. Therefore it allowed an easier process control and a wider dynamic doping range. Our process is an interesting route for the epitaxy of a low-resistance emitter layer for bipolar transistor application

Vapor phase doping with N-type dopant into silicon by atmospheric pressure chemical vapor deposition

peer reviewedAtomic layer doping of phosphorus (P) and arsenic (As) into Si was performed using the vapor phase doping (VPD) technique. For increasing deposition time and precursor gas flow rate, the P and As doses tend to saturate at about 0.8 and 1.0 monolayer of Si, respectively. Therefore, these processes are self-limited in both cases. When a Si cap layer is grown on the P-covered Si(001), high P concentration of 3.7 × 1020 cm-3 at the heterointerface in the Si- cap/P/Si-substrate layer stacks is achieved. Due to As desorption and segregation toward the Si surface during the temperature ramp up and during the Si-cap growth, the As concentration at the heterointerface in the Si-cap/As/Si-substrate layer stacks was lower compared to the P case. These results allowed us to evaluate the feasibility of the VPD process to fabricate precisely controlled doping profiles

Growth of high quality InP layers in STI trenches on miscut Si (001) substrates

In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [-1 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [-1 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2