James Jordan Rosenberg

An In 0.15 Ga 0.85 As/GaAs pseudomorphic single quantum well HEMT

This letter describes high electron mobility transistors (HEMTs) utilizing a conducting channel which is a single In<inf>0.15</inf>Ga<inf>0.85</inf>AS quantum well grown pseudomorphically on a GaAs substrate. A Hall mobility of 40 000 cm²/V.s has been observed at 77 K. Shubnikov-de Haas oscillations have been observed at 4.2 K which verify the existence of a two-dimensional electron gas at the In<inf>0.15</inf>Ga<inf>0.85</inf>As/GaAs interface. HEMTs fabricated with 2-µm gate lengths show an extrinsic transconductance of 90 and 140 mS/mm at 300 and 77 K, respectively-significantly larger than that previously reported for strained-layer superlattice In<inf>x</inf>Ga<inf>1-x</inf>As structures which are nonpseudomorphic to GaAs substrates. HEMTs with 1-µm gate lengths have been fabricated, which show an extrinsic transconductance of 175 mS/mm at 300 K which is higher than previously reported values for both strained and unstrained In<inf>x</inf>Ga<inf>1-x</inf>As FETs. The absence of Al<inf>x</inf>Ga<inf>1-x</inf>As in these structures has eliminated both the persistent photoconductivity effect and drain current collapse at 77 K.

Self-aligned germanium MOSFETs using a nitrided native oxide gate insulator

The fabrication and performance of dummy-gate self-aligned germanium MOSFETs utilizing a native germanium oxynitride gate insulator is reported. Based on device characteristics, channel mobility at 300 K is estimated as 940 cm/sup 2//Vs. Common-source characteristics show good saturation and turn-off, and do not exhibit looping or other anomalies. It is felt these results suggest that integration of germanium MOSFETs with photodiodes for monolithic optical-fiber receivers operating at 1.3- mu m wavelength should be possible. The results also indicate that the bulk mobility advantage which germanium exhibits relative to silicon carries over in some measure to FET channel mobility.<<ETX>>

p-channel germanium MOSFETs with high channel mobility

The fabrication and performance of p-channel germanium MOSFETs having a nitrided native oxide gate insulator are reported. A self-aligned dummy-gate process suitable for circuit integration is utilized. Common-source characteristics exhibit no looping and indicate a peak room-temperature channel mobility of 770 cm/sup 2//V-s. These results provide further evidence that a high-performance germanium CMOS technology is possible.<<ETX>>

Development and experimental verification of a two-dimensional numerical model of piezoelectrically induced threshold voltage shifts in GaAs MESFETs

The results of a combined experimental and analytical investigation of the effects of mechanical stress on DC electrical parameters, particularly threshold voltage, in MESFETs are reported. The theoretical aspect of this study involves a two-dimensional finite-element simulation of the device structure on which measurements were made. The substrate stresses and resultant piezoelectric charge distributions calculated in this study take into account the two-dimensional nature of the geometry of the gate. The experimental portion of this study involves measurement of DC parameters of devices using external mechanical loads that simulate mechanical stresses that arise during device processing. Measurements under applied loads of both signs and on devices of two different orientations confirm the existence of a piezoelectrically induced threshold voltage shift. A comparison between the approximate line load method of modeling substrate stress fields, and the finite-element method used in this study shows that the piezoelectric charge densities predicted by two models are substantially different. This results from the fact that the simplifying assumptions used to construct the line load model are inappropriate for accurately determining stress fields beneath micrometer and submicrometer gates. Good agreement was obtained between measured threshold voltage shifts and those predicted by the finite-element method model. The results show the need for accurate modeling of mechanical stresses when attempting to model piezoelectric effects. >

Importance of boundary conditions to conduction in short samples

The effects of boundary conditions on conduction in short samples are calculated numerically for nonballistic and ballistic cases. For the nonballistic case, the resistivity is substantially below the bulk value due to spillover from N+contacts even for samples which are several Debye lengths long. In the ballistic case, it is found that changing the boundary conditions strongly affects both the magnitude of the current and its dependence on voltage.

Modelling and experimental analysis of the impact of process induced stress on the electrical performance of GaAs MESFETs

Abstract A combination of two-dimensional Finite Element Methods and two-dimensional electronic device simulations was implemented to evaluate the effects of stress-induced piezoelectric charge distributions on the performance of GaAs MESFETs. This study takes into account the overlayer stresses a priori thus allowing an assessment of the impact of changes in device structural parameters on the electrical characteristics of the device. A qualitative explanation for the dependency of both threshold voltage and subthreshold current slope on dielectric overlayer thickness is put forward. It is confirmed that a predominantly negative charge distribution under the gate region is preferable to a positive one as device performance is less sensitive to structural parameter variations.

A Ka-band grid amplifier module with over 10 Watts output power

We present a Ka-band grid amplifier power module. The module is fully packaged with waveguide input and output flanges. It includes a driver grid amplifier chip for gain, followed by a booster grid amplifier chip for power. With a 50/spl deg/C baseplate temperature, the module has a small signal gain of 12 dB. The single-chip output booster stage delivers over 16 Watts of saturated power. The module delivers over 10 Watts output with a constant 1.6 Watts input over a 550 MHz bandwidth. We also present a large-signal third-order intermodulation and AM/PM conversion measurements, which are consistent with expectations. To our knowledge, this is the highest power ever reported from a monolithic single-chip power amplifier at Ka-band.

Investigation of stress effects on the direct current characteristics of GaAs metal‐semiconductor field‐effect transistors through the use of externally applied loads

This letter describes an experimental investigation of the effects of mechanical stress on the direct current (dc) electrical parameters in GaAs metal‐semiconductor field‐effect transistors, with the aim of separating out those effects which are direct manifestations of residual stresses in the completed device (e.g., piezoelectric effects) from stress effects which manifest themselves during the device processing (e.g., stress‐enhanced diffusion during implant annealing). This study extends previous work by examining individual transistors under both tensile and compressive loads. Systematic yet nonmonotomic variations in the dc parameters observed in several devices also suggest the possibility of defect generation in the device structures, even at relatively low bulk stresses.

Evaluation of device quality germanium‐germanium oxynitride interfaces by high‐resolution transmission electron microscopy

Previous work has shown that germanium oxynitride films grown on Ge substrates by thermal oxidation followed by nitridation provide a passivating dielectric which can be used to fabricate metal‐oxynitride‐semiconductor field‐effect transistors. We have investigated the interfacial microstructure of this semiconductor‐dielectric system with high‐resolution transmission electron microscopy (TEM) and show that 21‐nm‐thick germanium oxynitride films grown using this technique are uniform in thickness and interfacially smooth on a scale of ±0.5 nm over lateral peak‐to‐peak distances on the order of 100’s of nm. The germanium oxynitride was seen to be electron beam sensitive with significant damage to both the oxynitride and the semiconductor‐insulator interface being observed after exposure for 15 s to 200 keV electrons at a current density of 2.250 A/cm2 at the specimen.

Germanium p-channel MOSFET's with high channel mobility, transconductance, and k-value

Summary form only given. The authors report p-channel germanium MOSFETs which exhibit channel mobilities more than four times higher than typically obtained in p-channel silicon devices (in excess of 1000 cm/sup 2//V-s with a gate dielectric thickness of approximately 220 AA). Fabrication of these MOSFETs is quite straightforward and utilizes equipment which is comparable to that used for conventional silicon MOSFET processing. Germanium p-channel MOSFETs having effective channel lengths down to approximately 2.3 mu m (2.75- mu m gate length) have been fabricated. Using a dielectric capacitance of 2.5*10/sup -7/ F-cm/sup -2/ taken from large area devices, a mobility of approximately 1050 cm/sup 2//V-s can be inferred from the slope of the transconductance curve. For the 2.3- mu m device, a transconductance of 50 mS/mm at approximately 0.5 V above threshold and a k-value of 110 mS/V-mm have been obtained. This performance is significantly better than that of p-channel silicon devices having similar channel length and approximately 220-AA gate dielectric thickness. >