D. A. Grützmacher

Ge segregation in SiGe/Si heterostructures and its dependence on deposition technique and growth atmosphere

Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary‐ion‐mass‐spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800u2009°C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515u2009°C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800u2009°C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.

Impact of nanometer-scale roughness on contact-angle hysteresis and globulin adsorption

Besides surface chemistry, the surface roughness on the micrometer scale is known to dominate the wetting behavior and the biocompatiblity properties of solid-state materials. The significance of topographic features with nanometer size, however, has yet to be demonstrated. Our approach is based on well-defined Ge nanopyramids naturally grown on Si(001) using ultrahigh vacuum chemical vapor deposition, where the nanopyramid density can be precisely controlled by the growth conditions. Since the geometry of the nanopyramids, often termed dome clusters, is known, the surface roughness can be characterized by the Wenzel ratio with previously unattainable precision. Dynamic contact-angle measurements and adsorption of γ-globulin as a function of that ratio demonstrate the strong correlation between surface nanoarchitecture, on one hand, and wetting behavior and biocompatibility, on the other hand. Related x-ray photoelectron spectroscopy measurements reveal that potential changes of surface composition can be...

Selective SiGe and heavily As doped Si deposited at low temperature by atmospheric pressure chemical vapor deposition

Selective epitaxial Si with added As for n‐type doping or Ge for band gap modulation can be deposited in an ultraclean atmospheric pressure chemical vapor deposition system down to temperatures as low as 550–750u2009°C. Depositions are carried out in a hydrogen ambience using dichlorosilane, HCl, and arsine or germane. The additives, arsine and germane enhance the Si deposition rate at low temperatures so that practical deposition rates can be achieved. HCl, which is used to control deposition selectivity with respect to oxide or nitride, decreases the deposition rate so that final growth rates are in the range 1–5 nm/min. Rutherford backscattering spectrometry was used to measure As concentrations as high as 1×1021/cm3 and Ge concentrations as high as 50%. A selective growth process for SiGe has been used to grow p‐type metal–oxide–semiconductor field effect transistors and resonant tunneling diodes which display excellent device characteristics.

Cyclotron resonance studies of two-dimensional holes in strained Si1-xGex/Si quantum wells

Far‐infrared magnetotransmission spectroscopy has been employed to study p‐type modulation‐doped strained Si1−xGex/Si quantum wells grown by atmospheric pressure chemical vapor deposition at magnetic fields up to 23 T. The cyclotron resonance (CR) mass of the two‐dimensional hole gas (2DHG) in a strained 7.5 nm Si0.63Ge0.37 quantum well was determined to be (0.29±0.02)m0 for a 2D hole density of 2.3×1012/cm2 at 3 K. The CR mass of 2DHGs in strained Si1−xGex is comparable to previous measurements of the CR mass of 2DHGs in strained InyGa1−yAs with similar 2D hole densities.

High-performance emitter-up/down SiGe HBT's

The experimental results in this paper provide evidence of high-performance symmetric and emitter-down operation of SiGe-HBTs. SiGe-base transistors were fabricated by using Atmospheric-Pressure Chemical Vapor Deposition (APCVD) for the epitaxial growth of SiGe and Si layers, and a novel self-aligned device structure. Current gains of 2000 and 120, cutoff-frequencies of 64 GHz and 14 GHz, and maximum oscillation frequencies of 23 GHz and 10 GHz have been achieved for emitter-up and emitter-down operation, respectively.<<ETX>>

Selective growth of Si/SiGe resonant tunneling diodes by atmospheric pressure chemical vapor deposition

Atmospheric pressure chemical vapor deposition is used to grow p‐type Si/Si1−xGex double‐barrier resonant tunneling structures on unstrained substrates, with a Si0.75Ge0.25 well clad by Si barriers. The current‐voltage I(V) characteristics at T=77 and 4.2 K exhibit current peaks and negative differential resistance regions corresponding to resonant tunneling through well‐resolved heavy‐ and light‐hole subbands in the well. Device quality is comparable to Si/SiGe resonant tunneling structures grown by molecular beam epitaxy. The in situ substrate cleaning and selective growth capabilities of atmospheric pressure chemical vapor deposition are used for the first successful selective growth of resonant tunneling structures through an oxide mask. The resulting diodes exhibit good resonant tunneling characteristics. The selective growth process is promising for the fabrication of small vertical heterostructure devices.

Boron redistribution in arsenic‐implanted silicon and short‐channel effects in metal–oxide–semiconductor field effect transistors

When a high dose of As is implanted (e.g., 25 keV, 3×1015 cm−2) into B‐doped Si and the sample is subsequently annealed at 900u2009°C/5 min, pronounced segregation of the B into the implanted region occurs. This creates a B‐depleted region beyond the As profile. It is demonstrated that the B segregation is driven primarily by the implantation induced damage rather than by As‐B chemical and/or by electric field effects. The B segregation is nearly complete after a relatively low temperature (≲600u2009°C/30 min) anneal. Two‐dimensional device simulations show that the B depletion observed here can account for ≂50 mV threshold voltage roll off (at a drain bias of 0.1 V) in a Si metal–oxide–semiconductor field effect transistor of 0.2 μm gate length.

Cyclotron effective mass of holes in Si1−xGex/Si quantum wells: Strain and nonparabolicity effects

The Ge‐composition dependence of cyclotron effective mass of quasi‐two‐dimensional holes in strained Si1−xGex/Si quantum well structures has been investigated by far‐infrared magneto‐optical spectroscopy at low temperatures and high magnetic fields up to 23 T. The in‐plane effective mass determined from cyclotron resonance energies is much less than that of unstrained Si1−xGex alloys and decreases systematically from 0.40me to 0.29me as the Ge composition increases from x=0.13 to x=0.37, indicating the importance of the strain effect on the valence‐band structure. The nonparabolicity correction is significant in explaining the discrepancy between the measured values and the calculated band‐edge masses.

Very narrow SiGe/Si quantum wells deposited by low‐temperature atmospheric pressure chemical vapor deposition

The optical, structural, and electrical properties of very narrow SiGe quantum wells grown by ‘‘ultra‐clean’’ atmospheric pressure chemical vapor deposition (APCVD) are investigated. X‐ray reflectivity data reveal abrupt interfaces with a root‐mean‐square roughness of not more than 0.2 nm. For the first time narrow (4.3 meV) excitonic photoluminescence (PL) spectra were obtained from APCVD grown samples containing SiGe wells with 12.5% to 32.5% Ge. For the narrowest wells PL doublets are observed which are attributed to atomic steps at the SiGe/Si interfaces. The PL and x‐ray diffractometry data show that process deposition control for well and barrier width is within the monolayer range. Resonant tunneling diodes fabricated with 2.5‐mm‐wide Si0.75Ge0.25 wells show world record peak to valley ratios of 4.2. Magneto‐transport measurements performed at high magnetic fields of two‐dimensional hole gases exhibit pronounced Hall plateaus and well‐defined Shubnikov de Hass oscillations, indicating high material...

Fabrication of three‐terminal resonant tunneling devices in silicon‐based material

Laterally gated three‐terminal resonant tunneling devices have been fabricated from Si/Si1−xGex double‐barrier structures grown by atmospheric pressure chemical vapor deposition. The gate is insulated from the submicrometer vertical channel by a low‐temperature oxide and the entire fabrication scheme is compatible with current silicon technology. At T=77 K the resonant peak current can be modulated by 25% by applying a moderate gate voltage; at T=4.2 K, current modulation reaches 50%. We present calculations demonstrating that devices fabricated from optimized Si/Si1−xGex structures will pinch off fully at moderate gate voltages and operate at liquid nitrogen temperatures.