Samuel A. Alterovitz

Variable angle of incidence spectroscopic ellipsometry: Application to GaAs‐AlxGa1−xAs multiple heterostructures

The sensitivity of spectroscopic ellipsometry data to multilayer model parameters is shown to be a strong function of the angle of incidence. A quantitative study of sensitivity versus angle of incidence is performed for a GaAs‐AlxGa1−xAs‐GaAs substrate structure, showing that maximum sensitivity to layer thicknesses and AlGaAs composition occurs near the wavelength‐dependent principal angle. These results are verified by experimental measurements on two molecular‐beam epitaxy grown samples. New spectral features, not found in previous ellipsometry studies of similar structures, are also reported.The sensitivity of spectroscopic ellipsometry data to multilayer model parameters is shown to be a strong function of the angle of incidence. A quantitative study of sensitivity versus angle of incidence is performed for a GaAs‐AlxGa1−xAs‐GaAs substrate structure, showing that maximum sensitivity to layer thicknesses and AlGaAs composition occurs near the wavelength‐dependent principal angle. These results are verified by experimental measurements on two molecular‐beam epitaxy grown samples. New spectral features, not found in previous ellipsometry studies of similar structures, are also reported.

Modeling AlxGa1−xAs optical constants as functions of composition

Three models for the dielectric function ex(hν) of AlxGa1−xAs are reviewed. All are based on measured optical constants at discrete compositions. The validity of each model near critical point energies, and otherwise, is evaluated. Only the energy‐shift model is appropriate over the entire available spectrum (1.5–6.0 eV), including the band‐gap (E0) region.

X- and Ku-band amplifiers based on Si/SiGe HBT's and micromachined lumped components

A double mesa-structure Si/SiGe heterojunction bipolar transistor (HBT) and novel micromachined lumped passive components have been developed and successfully applied to the fabrication of X- and Ku-band monolithic amplifiers. The fabricated 5/spl times/5 /spl mu/m/sup 2/ emitter-size Si/SiGe HBT exhibited a DC-current gain /spl beta/ of 109, and f/sub T/ and f/sub max/ of 28 and 52 GHz, respectively. Micromachined spiral inductors demonstrated resonance frequency of 20 GHz up to 4 nH, which is higher than that of conventional spiral inductors by a factor of two. Single-, dual-, and three-stage X-band amplifiers have been designed, based on the extracted active- and passive-device model parameters. A single-stage amplifier exhibited a peak gain of 4.0 dB at 10.0 GHz, while dual- and three-stage versions showed peak gains of 5.7 dB at 10.0 GHz and 12.6 dB at 11.1 GHz, respectively. A Ku-band single-stage amplifier has also been designed and fabricated, showing a peak gain of 1.4 dB at 16.6 GHz. Matching circuits for all these amplifiers were implemented by lumped components, leading to a much smaller chip size compared to those employing distributed components as matching elements.

A high-power and high-gain X-band Si/SiGe/Si heterojunction bipolar transistor

A double mesa-type Si/SiGe/Si (n-p-n) heterojunction bipolar transistor (HBT) with record output power and power gain at X-band (8.4 GHz) is demonstrated. The device exhibits collector breakdown voltage BV/sub CBO/ of more than 24 V and a maximum oscillation frequency f/sub max/ of 37 GHz. Under continuous-wave operation and class-AB biasing conditions, 24.2-dBm (263-mW) RF output power with concurrent gain of 6.9 dB is measured at the peak power-added efficiency (28.1%) from a single ten-emitter fingers (780-/spl mu/m/sup 2/ emitter area) common-base HBT. The maximum RF output power achieved is as high as 26.3 dBm (430 mW in saturation) and the maximum collector efficiency is 36.9%. The low collector doping concentration together with the device layout result in negligible thermal effects across the transistor and greatly simplifies the large-signal modeling. The conventional Gummel-Poon model yields good agreement between the modeled and the measured de characteristics and small-signal S-parameters. The accuracy of the model is further validated with the measured power performance of the SiGe power HBT at X-band. These results set a benchmark for power performance for SiGe-based HBTs and indicate promise for their implementation in efficient X-band power-amplifier circuits.

Spectroscopic ellipsometry studies of HF treated Si (100) surfaces

Both ex situ and in situ spectroscopic ellipsometry (SE) measurements have been employed to investigate the effects of HF cleaning on Si surfaces. The hydrogen‐terminated (H‐terminated) Si surface was modeled as an equivalent dielectric layer, and monitored in real time by SE measurements. The SE analyses indicate that after a 20‐s 9:1 HF dip without rinse, the Si (100) surface was passivated by the hydrogen termination and remained chemically stable. Roughness of the HF‐etched bare Si (100) surface was observed, in an ultrahigh vacuum (UHV) chamber, and analyzed by the in situ SE. Evidence for desorption of the H‐terminated Si surface‐layer, after being heated to ∼550 °C in the UHV chamber, is presented and discussed. This is the first use of an ex situ and in situ real‐time, nondestructive technique capable of showing state of passivation, the rate of reoxidation, and the surface roughness of the H‐terminated Si surfaces.

Plasma-deposited amorphous hydrogenated carbon films and their tribological properties

Recent work on the properties of diamondlike carbon films and their dependence on preparation conditions are reviewed. The results of the study indicate that plasma deposition enables one to deposit a variety of amorphous hydrogenated carbon (a-C:H ) films exhibiting more diamondlike behavior to more graphitic behavior. The plasma-deposited a-C:H can be effectively used as hard, wear-resistant, and protective lubricating films on ceramic materials such as Si(sub 3)N(sub 4) under a variety of environmental conditions such as moist air, dry nitrogrn, and vacuum.

Mechanical strength and tribological behavior of ion-beam-deposited boron nitride films on non-metallic substrates

Abstract An investigation was conducted to examine the mechanical strength and tribological properties of boron nitride (BN) films ion-beam-deposited on silicon, fused silica (SiO 2 ), gallium arsenide (GaAs) and indium phosphide (InP) substrates in sliding contact with a diamond pin under a load. The results of the investigation indicate that BN films on non-metallic substrates, like metal films on metallic substrates, deform elastically and plastically in the interfacial region when in contact with a diamond pin. However, unlike metal films and substrates, BN films on non-metallic substrates can fracture when they are critically loaded. Not only does the yield pressure (hardness) of silicon and SiO 2 substrates increase by a factor of two in the presence of a BN film, but the critical load needed to fracture also increases. The presence of films on the brittle substrates can arrest crack formation. The BN film reduces adhesion and friction in the sliding contact. BN adheres to silicon and SiO 2 and forms a good quality film, but it adheres poorly to GaAs and InP.

Characteristics of 0.8- and 0.2- mu m gate length In/sub x/Ga/sub 1-x/As/In/sub 0.52/Al/sub 0.48/As/InP (0.53<or=x<or=0.70) modulation-doped field-effect transistors at cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53 >

High-temperature RF probe station for device characterization through 500/spl deg/C and 50 GHz

A high-temperature measurement system capable of performing on-wafer microwave testing of semiconductor devices has been developed. This high-temperature probe station can characterize active and passive devices and circuits at temperatures ranging from room temperature to above 500/spl deg/C. The heating system uses a ceramic heater mounted on an insulating block of NASA Shuttle tile. The temperature is adjusted by a graphical computer interface and is controlled by the software-based feedback loop. The system is used with a vector network analyzer to measure scattering parameters over a frequency range from 1 to 50 GHz. The microwave probes, cables, and inspection microscope are all shielded to protect from heat damage. The high-temperature probe station has been successfully used to characterize gold transmission lines on silicon carbide at temperatures up to 540/spl deg/C.

Variable angle spectroscopic ellipsometry: Application to GaAs‐AlGaAs multilayer homogeneity characterization

Variable angle spectroscopic ellipsometry has been applied to a GaAs‐AlGaAs multilayer structure to obtain a three‐dimensional characterization using repetitive measurements at several spots on the same sample. The reproducibility of the layer thickness measurements is of order 10 A, while the lateral dimension is limited by beam diameter, presently of order 1 mm. Thus, the three‐dimensional result mainly gives the sample homogeneity. In the present case we used three spots to scan the homogeneity over 1 in. of a wafer, which had molecular‐beam epitaxially grown layers. The thickness of the AlGaAs, GaAs, and oxide layers and the Al concentration x varied by 1% or less from edge to edge. This result was confirmed by two methods of data analysis. No evidence of an interfacial layer was observed on top of the AlGaAs.