Simulations and measurements of submicron pseudomorphic high electron mobility transistors (HEMT's) are presented. For the simulations the generic device simulator MINIMOS-NT is used which is capable of dealing with complex device geometries as well as with several physical models represented by certain sets of partial differential equations. A description of the structure of the simulator is given, which shows the basic idea of splitting the device geometry into distinct regions. Within these "segments," arbitrary material properties and physical models, i.e., partial differential equations, can be defined independently. The segments are linked together by interface models which account for the interface conditions. The simulated characteristics of a HEMT with a gate length of 240 nm are compared with the measured data. Essential physical effects which determine the behavior of the device can be identified in the output and transfer characteristics.

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Measurements and simulations of three different pseudomorphic high electron mobility transistors (PHEMT's) are presented. The PHEMT's possess the same epitaxial structure but different geometrical properties. For the simulations, the generic device simulator MINIMOS-NT is employed. This simulator is not restricted to planar device surfaces but is able to model complex surface topologies including the effect of passivating dielectric layers. Mixed hydrodynamic and drift-diffusion simulations are demonstrated. They include the DC characteristics as well as the bias-dependent gate capacitances. Thus, biasdependent current-gain cutoff frequencies f T can be calculated. The results compare very well with the values obtained by small-signal parameter extractions from S-parameter measurements. Although a single consistent set of parameters is used for the simulations of all three devices, their characteristics are reproduced with an accuracy to our knowledge not reported before. Therefore, the DC and RF properties of PHEMT's with geometries significantly different from the measured devices can be reliably predicted.

Today's GaAs PHEMTs make it possible to cover applications of an extremely wide frequency range, as high as 100 GHz, with a single device type. In this paper, a set of models and calibrations for the predictive device simulation of GaAs PHEMTs is developed. The simulation setup includes a description of the device geometry. In particular, a realistic representation of the region between the ohmic contacts and the channel is included along with the fitting procedure of the simulation parameters and the necessary transport and interface models. In addition, special emphasis has been placed on a simultaneous fitting of currents and capacitances. The resulting setup allows to describe different devices without changing any nontechnology dependent parameters and thus provides a global calibration within a given device family. This capability is demonstrated by comparing the measured and simulated results of five very different devices which cover gate lengths from 120 to 500 nm, transconductances from 400 to 800 mS/mm, and ungated channel lengths from 70 to 600 nm Index Terms-Calibration, GaAs, millimeter wave devices, MODFET, semiconductor heterojunctions, simulation. I. INTRODUCTIONT HE GaAs wafer industry has experienced phenomenal growth over the last few years [1]. Today, MESFETs are the working horse for most large volume applications. As the demands on device performance are increased other transistors like pseudomorphic HEMTs (PHEMTs) and HBTs are becoming very important.PHEMTs on GaAs are able to cover an extremely wide frequency range with very good competitiveness over other technologies. Depending on the application, different requirements arise. The lower important frequency range 0.9/1.9 GHz is used for mobile communication where HEMTs are competing with various other technologies such as LDMOS, Si/Ge-HBTs, III-V-HBTs, and GaAs-MESFETs. Therefore, cheap volume production is one of the most important requirements. These HEMTs will typically have gate lengths between 500 nm and 1 m and breakdown voltages over 10 V. Frequency bands around 40 GHz for base stations lead to a trade off between RF performance and power capability. HEMTs for applications around 77 GHz and 94 GHz are usually optimized in first place with respect to their RF performance. Therefore, they typically exhibit gate lengths below 150 nm and breakdown voltages around 5 V.

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