The surface barrier heights φbn and room-temperature band gaps Eg of Si-doped InxAl1−xAs layers grown by molecular beam epitaxy on n-type (100) oriented InP substrates have been determined as a function of composition with capacitance versus voltage, internal photoemission, photoluminescence, and double-crystal x-ray rocking curve measurements for 0.45<x<0.55. The results indicate that Eg and φbn are linear functions of x; they also suggest that φbn (0.78)=0 and, for x>0.78, n-type surfaces might be accumulated and p-type surfaces are likely to be inverted.

The conduction-band discontinuity (ΔEc ) and the band-gap offset (ΔEgh) of InxGa1−xAs/GaAs multiple quantum wells grown on GaAs substrates by molecular beam epitaxy are investigated for 0<x<0.3. The band gap of strained InxGa1−xAs , determined from the excitonic transition of room-temperature transmission spectra, is found to be linearly dependent on x and is in good agreement with the calculated values. The band-gap offset is found to be ΔEgh =1.15x eV. The conduction-band offset, compiled from published data, is ΔEc =0.75x eV, and thus (ΔEc /ΔEgh)=0.65 independent of x.

POWER CONSUMPTION OF EMBEDDED SRAM is a significant concern in state-of-the-art processors. Lowering the supply voltage (V DD ) effectively saves power. However, V DD scaling for conventional SRAM is limited by the random variation of the device threshold voltage (V TH ), because of random dopant fluctuation (RDF) effects, which are expected to increase with technology scaling. On the other hand, high doping is not required for multigate devices such as FinFETs. 1 In such devices, V TH variation is smaller and V DD can be scaled to lower voltages. 2 These devices will likely be used in future CMOS technologies. In the absence of RDF, variation in V TH will originate mainly from the lithography-defined gate length (L) and fin thickness (T fin ). It is crucial that these variation sources in multigate devices are modeled.Numerical simulations based on finite-element methods or TCAD (technology CAD) tools are useful for technology evaluation and design exploration of FinFET-based SRAM cells (see, for example, the work by Guo et al. 3 ). Mixed-mode TCAD simulations can be combined with Monte Carlo simulations to predict the impact of device variation on circuit performance. Many simulations are needed, however, and such a task is time-consuming. An efficient compact model (or Spice model) such as BSIM-CMG is more suitable. 4 The model employs physical expressions to capture the effect of device parameters such as L and T fin on the electrical characteristics of multigate devices. Through proper parameter extraction, the effects of these variation sources can be captured.In this article, we present a procedure to model variation in FinFET SRAM cells using BSIM-CMG, which we used in a study for the design and optimization of a six-transistor (6T) FinFET SRAM cell. We review design considerations of FinFET SRAM cells and the advantages of multigate devices, and give a brief overview of BSIM-CMG. We explain the process of separating global and local variation components and of calibrating variation to data. SRAM design considerationsFour design metrics quantify the read/write stability and performance of an SRAM cell (see Figure 1a):A read static noise margin characterizes the read stability of the SRAM cell. The RSNM is defined as the side length of the maximum square that can fit inside the butterfly curve (see Figure 1b). We form a butterfly curve by plotting the voltage transfer characteristics of the two inverters in an SRAM cell when both the bit line (BL) and word line (WL) are biased at V DD . If the two squares inside the butterfly curve do not have equal side lengths, we define RSNM as the side length of the smaller square. Compact Variability Modeling for Nanometer CMOS TechnologyEditor's note: FinFET technology is a possible solution to achieve a better power/performance trade-off for SRAM cells. This article provides a comprehensive analysis of the variations in FinFET devices, their impact on SRAM stability, and a statistical design procedure for FinFET SRAM cells.

We have measured the photoreflectance (PR) spectrum at 300 K from a lattice-matched InP/InGaAs heterojunction bipolar transistor structure grown by gas-source molecular beam epitaxy. From the observed Franz–Keldysh oscillations we have evaluated the built-in dc electric fields and associated doping profiles in the n-InGaAs collector and n-InP emitter regions. These donor concentrations are in agreement with capacitance-voltage and secondary ion mass spectroscopy determinations, but are considerably lower than the intended values from the growth parameters. We have thereby detected a failure of the Si doping source which occurred during material growth using this contactless, nondestructive, and rapid characterization method. The energy of the InGaAs band gap from the PR spectrum also verifies the lattice-matched nature of the system, further demonstrating the diagnostic and process control value of the PR technique.

The Schottky barrier height of n-type semiconducting and semi-insulating InxAl1−xAs grown by molecular beam epitaxy has been determined on the lattice-matched composition, x=0.523, in tension and in compression relative to their (110) oriented InP substrates. For the semiconducting material in the composition range 0.43<x<0.62, the barrier height is φbn=0.62±0.05 eV while the anomalous rise and saturation of φbn at 1.2 eV of the semi-insulating material, within the same composition range, is attributed to the presence of AlAs clusters within an InxAl1−xAs matrix.

The conduction-band offsets ΔEc of n-isotype InxAl1−xAs/In0.53Ga0.47As heterojunctions, with 0.47<x≤0.52, grown by molecular-beam epitaxy, lattice matched and pseudomorphically strained on n+-InP substrates, were determined from the capacitance-voltage profiling technique. A more accurate ΔEc value was obtained after the correction for fixed interface charge perturbation. The ΔEc related to the band-gap difference ΔEgs of the heterojunction are found to be ΔEc=0.70ΔEgs. The fixed interface charges are acceptorlike with a density of the order 1010/cm2.

A methodology based on the transistor body effect is used to monitor inversion oxide thicknesses (T inv 's) in high-κ/metal-gate undoped ultrathin-body short-channel SOI FINFETs. The extracted T inv 's are benchmarked to independent capacitance-voltage (C-V ) measurements. For the first time, device simulation is introduced to understand the fundamental difference in T inv values extracted using the two techniques, which is driven by the inversion charge centroid at different bias conditions. Index Terms-Fully depleted SOI (FDSOI), FINFETs, inversion oxide thickness, ultrathin body.

The persistent photoinduced changes in the critical temperature TC and the normal state conductivity of (Y0.5Ca0.5)Ba2Cu3Oδ thin films are studied. Previously such effects have been observed only in underdoped YBa2Cu3Oδ or YSrxBa2−xCu3Oδ, which always lead to the enhancement of both TC and conductivity. The current system can be doped from the underdoped regime to the overdoped regime by increasing its oxygen content. The photoinduced TC reduction in the overdoped films is observed. The simultaneous enhancement of conductivity is consistent with the interpretation that photoillumination always increases hole concentration in the “123” systems.