Advanced epitaxial growth techniques permit the use of pseudomorphic Si/sub 1-x/Ge/sub x/ alloys in silicon technology. The smaller bandgap of these alloys allows for a variety of novel band-engineered structures that promise to enhance silicon-based technology significantly. The authors discuss the growth and properties of pseudomorphic Si/sub 1-x/Ge/sub x/ structures and then focus on their applications, especially the Si/sub 1-x/Ge/sub x/-base heterojunction bipolar transistor (HBT). They show that HBTs in the Si/sub 1-x/Ge/sub x/ system allow for the decoupling of current gain and intrinsic base resistance. Such devices can be made by using a variety of techniques, including molecular-beam epitaxy and chemical vapor deposition. The authors describe the evolution of fabrication schemes for such HBTs and describe the DC and AC results obtained. They show that optimally designed HBTs coupled with advanced bipolar structures can provide performance leverage. >

Heterojunction bipolar transistors using Si-Ge alloys

The authors demonstrate the feasibility of a p-channel quantum-well MOSFET on a Ge/sub x/Si/sub 1-x//Si heterostructure. The advantages of the enhancement-mode p-channel MOSFET device compared to GeSi MODFETs are its high impedance, channel mobility, and channel transconductance. The device shows good saturation and cutoff behaviour. A saturation transconductance of 64 mS/mm was measured for a 0.7- mu m channel device at a drain-to-source voltage of -2.5 V. The channel mobility was found to be higher than that of a similarly processed Si p-channel MOSFET. >

Enhancement-mode quantum-well Ge/sub x/Si/sub 1-x /PMOS

The use of strained layer epitaxy to grow high-quality Ge/sub x/Si/sub 1-x//Si heterostructures and their application to a wide range of heterostructure devices are addressed. The author reviews the mechanisms of strained layer growth, the bandstructure of the resulting material, and its use in test devices, including superlattice avalanche photodiodes for fiber optic communication, intrasubband optical detectors and arrays operating in the 10-15 mu m wavelength range, mobility enhanced modulation-doped transistors, heterojunction bipolar transistors with cutoff frequencies of 75 GHz, and negative resistance devices based on resonant tunneling and real-space carrier transfer. >

Silicon-based semiconductor heterostructures: column IV bandgap engineering

Silicon-Based Semiconductor He teros tructures: Column IV Bandgap Engineering

The oxidation of SiGe layers grown by molecular beam epitaxy was studied. Auger depth profile showed that after oxidation, Ge was completely rejected from the oxide and Ge‐rich layers were formed. However, the Ge concentration in the SiGe layer was found to play an important role in the formation of these Ge‐Rich layers. For SiGe with Ge concentration below 50%, Si was preferentially oxidized and only one Ge‐rich layer was formed at the oxide/substrate interface. On the other hand, for SiGe with Ge concentration above 50%, two Ge‐rich layers were formed after oxidation with one at the oxide/substrate interface and the other at the oxide surface. X‐ray photoelectron spectroscopy studies showed that Ge at the oxide/substrate interface is in elemental form, while Ge at the oxide surface is in an intermediate oxidized state. A classical binary alloy oxidation theory is employed to explain the overall oxidation behavior qualitatively.

Effects of Ge concentration on SiGe oxidation behavior

Resonant tunneling of holes through an unstrained GeSi well between two strained Si barriers on a relaxed GeSi buffer layer has been observed for the first time. The peak‐to‐valley ratios of 2.1/1 at 4.2 K and 1.6/1 at 77 K in current‐voltage characteristics were attained for light holes. Resonant tunneling from heavy‐hole states was also observed at room temperature, as well as 77 and 4.2 K by conductance measurement. The positions of the resonance peaks are in good agreement with the light‐ and heavy‐hole bound states in the quantum well.

Resonant tunneling through a Si/GexSi1-x/Si heterostructure on a GeSi buffer layer

Abstract The temperature dependence of the low-energy magnetic excitations in the spin-triplet superconductor UTe 2 was measured via inelastic neutron scattering in the normal and superconducting states. These excitations have a peak instensity at 4 meV, follow the Brillouin zone edges near the crystallographic b-axis, obey the paramagnetic structural symmetry, and track the temperature evolution of the heavy fermion bulk magnetic susceptibility. Thus, the imaginary part of the dynamic susceptibility follows the behavior of interband correlations in a hybridized Kondo lattice with an appropriate characteristic energy. These excitations are a lower-dimensional analog of phenomena observed in other Kondo lattice materials, such that their presence is not necessarily due to dominance of ferromagnetic or antiferromagnetic correlations. The onset of superconductivity alters the magnetic excitations noticeably on the same energy scales, suggesting that these changes originate from additional electronic structure modification. 

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Q. Ye

Papers

Resonant tunneling through a Si/GexSi1-x/Si heterostructure on a GeSi buffer layer

Symmetry of magnetic correlations in spin-triplet superconductor UTe2