Abstract

Heterojunction Bipolar Transistors (HBTs) are among the most advanced semiconductor devices. They match well today's requirements for high-speed operation, low power consumption, high-integration, low cost in large quantities, and operation capabilities in the frequency range from 0.9 to 100 GHz. At present III-V HBT MMICs on six-inch wafers and SiGe HBT circuits as part of the CMOS technology on eight-inch wafers are in volume production. To cope with the explosive development costs of today's semiconductor industry Technology Computer-Aided Design (TCAD) methodologies are extensively used. Technology, device, and circuit simulation tools save expensive technological efforts while improving the device performance.

The thesis discusses the status of research regarding HBTs, including a review of state-of-the-art devices, a review of state-of-the-art device simulators, with emphasis on MINIMOS-NT, and a discussion on the materials and material systems on which HBTs are based on. MINIMOS-NT is a generic two-dimensional device/circuit simulator used in the VISTA TCAD framework. A large part of the work presented in this thesis is on the development and the practical application of MINIMOS-NT. A detailed discussion on the physical modeling in MINIMOS-NT is presented. It contains models for the lattice, thermal, and transport properties of various semiconductor materials, as well as models for several important effects taking place in HBTs. Critical issues concerning simulation of heterostructures are analyzed, such as interface modeling at heterojunctions and insulator surfaces, band structure and bandgap narrowing, the modeling of self-heating and high-field effects.

Simulation results for several different types of GaAs-based and Si-based HBTs demonstrating the extended capabilities of MINIMOS-NT are shown, most of them in comparison with experimental data. Special emphasis is put on the simulation of high-power AlGaAs/GaAs and InGaP/GaAs HBTs. Two-dimensional DC-simulations of different types of one-finger devices in very good agreement with measured data in a wide temperature range are demonstrated. Self-heating effects are accounted for the output device characteristics. The work is extended with transient simulation of small signal parameters to connect DC- and RF- device operation. A comparison of simulated and measured S-parameters and the dependence of $f_{\mathrm{T}}$ on some device parameters are presented. Device reliability investigations which confirm the usefulness of device simulation for practical applications are also offered. Examples of SiGe HBTs and polysilicon emitter BJT conclude the work presented in the thesis.