Ultrathin silicon-on-insulator, composed of a crystalline sheet of silicon bounded by native oxide and a buried oxide layer, is extremely resistive because of charge trapping at the interfaces between the sheet of silicon and the oxide. After chemical modification of the top surface with hydrofluoric acid (HF), the sheet resistance drops to values below what is expected based on bulk doping alone. We explain this behavior in terms of surface-induced band structure changes combined with the effective isolation from bulk properties created by crystal thinness.

We demonstrate the feasibility of fabricating heterojunctions of semiconductors with high mismatches in lattice constant and coefficient of thermal expansion by employing nanomembrane bonding. We investigate the structure of and electrical transport across the interface of a Si/Ge bilayer formed by direct, low-temperature hydrophobic bonding of a 200 nm thick monocrystalline Si(001) membrane to a bulk Ge(001) wafer. The membrane bond has an extremely high quality, with an interfacial region of ∼1 nm. No fracture or delamination is observed for temperature changes greater than 350 °C, despite the approximately 2:1 ratio of thermal-expansion coefficients. Both the Si and the Ge maintain a high degree of crystallinity. The junction is highly conductive. The nonlinear transport behavior is fit with a tunneling model, and the bonding behavior is explained with nanomembrane mechanics.

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Abstract. The dependences of the 294 and 10 K mobility μ and volume carrier concentration n on thickness (d ¼ 25 to 147 nm) are examined in aluminum-doped zinc oxide (AZO). Two AZO layers are grown at each thickness, one with and one without a 20-nm-thick ZnON buffer layer. Plots of the 10 K sheet concentration n s versus d for buffered (B) and unbuffered (UB) samples give straight lines of similar slope, n ¼ 8.36 × 10 20 and 8.32 × 10 20 cm −3 , but different x -axis intercepts, δd ¼ −4 and þ13 nm, respectively. Plots of n s versus d at 294 K produce substantially the same results. Plots of μ versus d can be well fitted with the equation μðd Þ ¼ μð∞Þ∕½1 þ d à ∕ðd − δdÞ, where d à is the thickness for which μð∞Þ is reduced by a factor 2. For the B and UB samples, dà ¼ 7 and 23 nm, respectively, showing the efficacy of the ZnON buffer. Finally, from n and μð∞Þ we can use degenerate electron scattering theory to calculate bulk donor and acceptor concentrations of 1.23 × 10 21 cm −3 and 1.95 × 10 20 cm −3 , respectively, and Drude theory to predict a plasmonic resonance at 1.34 μm. The latter is confirmed by reflectance measurements.

SiGe/Si quantum wells are of great interest for the development of Group-IV THz quantum cascade lasers. The main advantage of Group-IV over III-V materials such as GaAs is that, in the former, polar phonon scattering, which significantly diminishes the efficiency of intersubband light emission, is absent. However, for SiGe/Si multiple-quantum-well structures grown on bulk Si, the lattice mismatch between Si and Ge limits the critical thickness for dislocation formation and thus the number of periods that can be grown. Similarly, the use of composition-graded SiGe films as a lattice-matched substrate leads to the transfer of dislocations from the graded buffer substrate into the quantum wells, with a consequent decrease in light emission efficiency. Here we instead employ nanomembrane strain engineering to fabricate dislocation-free strain relaxed substrates, with lattice constants that match the average lattice constants of the quantum wells. This procedure allows for the growth of many periods with excellent structural properties. The samples in this work were grown by low-pressure chemical vapor deposition and characterized via high-resolution X-ray diffraction and far-infrared transmission spectroscopy, showing narrow intersubband absorption features indicative of high crystalline quality.

Boron Nitride is a promising 2D dielectric material for use in numerous electronic applications. In order to realize this potential, a process for producing atomically thin layers on microelectronics-compatible substrates is desirable. In this paper we describe an approach to epitaxially grow few-layer sp 2 BN directly on an insulating substrate, using metal-organic chemical vapor deposition (MOCVD). We also elucidate the effect of sapphire surface nitridation on the growth characteristics. We compare the effect of nitridation on the growth rate, surface morphology and structure across a wide range of V/III ratios. Depending on the V/III ratio, two different growth modes were identified: at low V/III 3D island growth is dominant and at high V/III the growth transitions to a self-terminating mode. Under self-terminating growth a film thickness of 1.5 nm is typically achieved. Surface nitridation was found to improve nucleation, promoting self-terminating growth, and resulting in atomically smooth films. Reflection high energy electron diffraction (RHEED) patterns reveal the epitaxial relationship between BN and sapphire to be [1-100]‖[11-20] and [0001]‖[0001]. Growth at low V/III ratios without surface nitridation produced films with large hexagonal holes, which could not be completely filled by extending the growth time. Through surface nitridation, these holes were eliminated, producing continuous smooth films.

Because of the large surface-to-volume ratio, the conductivity of semiconductor nanostructures is very sensitive to surface chemical and structural conditions. Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared. The sheet resistance of the SiNMs, measured by the van der Pauw method, shows that HF etching produces at least an order of magnitude larger drop in sheet resistance than that caused by VH treatment, relative to the very high sheet resistance of samples terminated with native oxide. Re-oxidation rates after these treatments also differ. X-ray photoelectron spectroscopy measurements are consistent with the electrical-conductivity results. We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty

A remote plasma enhanced chemical vapor deposition (CVD) process using GeH 4 , SiH 4 , and SnCl 4 precursors has been developed for epitaxial growth of group-IV alloys directly on Si (100) substrates, without the need for buffer layers. X-ray diffraction measurements of a representative Ge 1−x Sn x sample which is 233 nm thick, with x = 9.6% show it to be highly oriented along the [001] direction and nearly relaxed, with 0.37% compressive strain. Ellipsometry measurements provide a pseudo-dielectric function which is well fitted by a 3-layer (substrate/alloy/surface oxide) model. Cross-sectional transmissionelectron-microscope images show a highly defective interface layer, ∼ 60 nm thick, containing edge dislocations and stacking faults; above this layer, the lattice is wellordered, with a much lower density of defects. Atomic force microscopy measurements show an RMS roughness of 1.2 nm for this film.