(B.Sc./M.Sc.) Design and Technology Development for THz Transistors in 6G Applications and Optoelectronic Front-Ends

Data rates in both wireless and fiber-optic transmission systems continue to increase exponentially. This demands carrier frequencies and bandwidths in the terahertz (THz) range—capabilities that cannot yet be achieved with existing transistor technologies.

This challenge can be addressed using indium phosphide (InP)-based transistors and tunnel diodes currently under development at our chair. A critical bottleneck limiting the speed of these chips is the electrical conductivity of the semiconductor material, as well as the contact resistance to these highly doped layers.  

Currently, the focus is on optimizing p-doped GaAsSb—a ternary alloy with an atomic lattice constant matching that of InP—enabling its integration into complex InP-based heterostructures. Supported by the EU JU CHIPS project Move2THz, InP/GaAsSb heterostructures for bipolar transistors are being realized via metalorganic chemical vapor deposition (MOCVD), alongside the development of corresponding chip fabrication processes.

In the context of bachelor’s and master’s theses (B.Sc./M.Sc.), students will analyze test layers using techniques such as X-ray diffraction, photoluminescence, and atomic force microscopy. Submicrometer test structures for contact resistance and high-frequency transistors will be fabricated using electron-beam lithography, plasma etching, and metal deposition, aiming to achieve optimal device performance.

The optimization process is carried out in the context of the complete device, including physical modeling of DC and high-frequency behavior, as well as comparison with physical simulations (TCAD). This research contributes to advancing next-generation THz electronics for future 6G wireless systems and optoelectronic front-ends.

Supervisor: M.Sc. Jan Ebbert

(B.Sc./M.Sc.) Implementation of Nanometer-Scale Lithography Processes for Scalable High-Frequency Devices

State-of-the-art semiconductor chips for AI accelerators, high-performance mobile processors, and similar applications feature structural dimensions on the order of 10 nm. Electron-beam lithography enables the fabrication of such nanoscale features. At our research group (BHE), a modern 100 keV electron-beam lithography system is operated, capable of achieving line widths below 10 nm and alignment accuracy between different lithographic layers at the 10 nm level.

In the electron-beam lithography process, desired patterns are transferred onto dose-sensitive resist layers using a focused electron beam. These resist layers are composed of various polymer systems. To optimize the lithography steps, different resist materials are systematically investigated on specialized substrates such as InP, sapphire, and glass. Electron scattering within both the substrate and resist layers is modeled using Monte Carlo simulation methods, and patterns are pre-corrected accordingly to compensate for scattering effects.

These lithography processes are integrated into device fabrication workflows for transistors and THz diodes within our group, and are also applied in joint technology development projects at the Joint Lab InP Devices at the Ferdinand-Braun-Institut (FBH), Berlin.

Nanoscale structure analysis is performed using a high-resolution scanning electron microscope (SEM) and atomic force microscopy (AFM). A key component of a bachelor’s or master’s thesis in this area includes training on the electron-beam lithography system, SEM, and AFM, as well as the use of the modeling software package “TRACER/BEAMER” for proximity effect correction.

This research contributes to the development of advanced nanoscale fabrication techniques essential for next-generation high-frequency and high-performance electronic devices.

Supervisor: M.Sc. Jan Ebbert

(B.Sc./M.Sc.) Development and Characterization of GaN-Based Devices

Nitrogen-containing compound semiconductors are generally referred to as nitride semiconductors. The most well-known compound here is Gallium Nitride (GaN), which forms the basis of modern lighting technology in the form of LEDs, among other applications. In addition to their high optoelectronic relevance, III-nitride semiconductors are utilized in high-performance devices, such as High Electron Mobility Transistors (HEMTs). A specific feature of nitride semiconductors lies in their crystal structure. In the material, a spontaneous and piezoelectric polarization field exists directionally. This is purposefully utilized for the fabrication of simple HEMTs but generally negatively impacts the efficiency of quantum devices, such as LEDs.

In our field, we are working on two GaN-based devices. One of these is the resonant tunneling diode (RTD) for applications in oscillator circuits. The other is a HEMT intended for use as a sensor. The work involves the development of the epitaxy of the devices using metal-organic vapor phase epitaxy (only Master's theses), corresponding planning and development of the technology, and the acquisition and application of suitable characterization methods in the various phases of device development. The results obtained will be used for model development and further optimization of the processes and devices.

If you are interested in the nitride devices, please feel free to contact us for more information.

Supervisor: Dr.-Ing. Patrick Häuser

(M.Sc.) Design of Integrated Circuits in InP Semiconductor Technologies

In the next-generation mobile communication standard (6G), frequency ranges from 110 GHz to 170 GHz and from 220 GHz to 330 GHz are to be utilized to achieve particularly high data transmission rates. Systems designed for these frequency ranges place especially high demands on the performance of the semiconductor technology used. Promising semiconductor technologies include indium phosphide (InP)-based double heterojunction bipolar transistor (DHBT) technologies. The DHBTs and passive components are employed to realize circuits for the transmission systems.

We design circuits using InP semiconductor technology and investigate various topologies to implement functions such as mixers, amplifiers, or oscillators for the specified frequency ranges.

Possible topics: Implementation and investigation of a circuit for the conversion of symmetric to asymmetric signals (Balun).

Supervisor: M.Sc. Konrad Müller

(M.Sc.) Precision Structuring of Robust TiW Contacts for InP High-Frequency Electronics with CMOS Compatibility

InP-based device technologies are of critical importance for optoelectronic applications—such as 1.55 µm lasers—as well as for wireless transmission beyond 6G frequencies in the D-band (110–170 GHz) and H-band (~300 GHz), enabling electronic THz circuits and THz sources. The heterogeneous integration of InP devices with CMOS technology allows combining the inherent advantages of InP (high-efficiency photonics and high-frequency electronics) with the high integration complexity and scalability of silicon-based CMOS processes. To enable this integration, CMOS-compatible process steps are essential—particularly the replacement of gold or platinum, which can contaminate CMOS fabrication lines, with CMOS-compatible materials, especially refractory metals such as tungsten (W).

In our group, TiW metal layers are deposited in a sputtering system and structured using plasma-based processes. A key focus of this work is the optimization of process parameters, including pre-treatment of semiconductor surfaces to ensure reliable adhesion and low contact resistance. The resulting structures are thoroughly characterized using a range of analytical techniques—such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM)—as well as test structures for contact resistance measurement (Transfer Length Method, TLM).

This research contributes to the development of robust, high-performance, and CMOS-compatible TiW contacts for next-generation InP-based high-frequency and optoelectronic devices, paving the way for advanced heterogeneous integration platforms.

Supervisor: M.Sc. Jan Ebbert

Here you will find a list of the project and thesis works that have been completed at our chair so far.

Completed Works 2025

Bachelor theses

• Optimization of p+ doped arsenide layers for application in MOCVD-grown InP DHBT structures (Assignment/Summary)

Master's theses

• Analysis and development of a communication link based on resonant tunneling diodes (Assignment/Summary)
• Development of MOVPE-grown InP-based layerstacks for resonant tunneling diodes (Assignment/Summary)
• Optimization of p-InGaAs Base Layers and Their Integration into an MOVPE Process for Submicrometer InP Double-Heterojunction Bipolar Transistors (DHBTs) (Assignment/Summary)
• Design of Deembedding Structures and a Frequency Doubler Circuit for Application in the Next-Generation Communication Standard (6G) (Assignment/Summary)

Master's project works

• Development of an RTD Module for the Electronic Readout of a Terahertz Biosensor (Assignment/Summary)

Completed Works 2024

Bachelor theses

• Investigation of Mouse Brain Slice in Presence of Terahertz RTD Oscillators and Detectors (Assignment/Summary)
• Development of lithography for sub-100 nm T-gate structures (Assignment/Summary)

Bachelor project works

• Electron beam lithography-based technology development of III-V semiconductor devices (Assignment/Summary)
• Extension of an automated wafer probe station for precise device characterization (Assignment/Summary)

Master's theses

• Design of a D-Band Power Amplifier in InP DHBT MMIC Technology (Assignment/Summary)
• Development of InP-based layer stacks for DHBTs based on a low-temperature MOVPE process (Assignment/Summary)
• Design of a D-Band down-conversion mixer based on InP-HBTs for 6G applications (Assignment/Summary)
• Design and realization of compact THz sources (Assignment/Summary)
• Development of a measurement routine for semiconductor characterization (Assignment/Summary)
• Development of back-to-back structures for characterization of flip-chip interfaces on InP and InP/SiGe technology (Assignment/Summary)
• Development of a novel control algorithm for a bidirectional drive inverter with minimized line-bound EM emission characteristics (Assignment/Summary)
• Design of low-noise amplifiers for application in the 6G standard (Assignment/Summary)

Master's project works

• Further development and optimization of III-V high-frequency devices (Assignment/Summary)
• Investigation of Nonlinear Dynamics of Resonant Tunneling Diode Oscillators (Assignment/Summary)
• Process Development of Passive RF Components realized in Microstrip Technology (Assignment/Summary)

Completed Works 2023

Bachelor theses

• Process Control of Contacting for Indium Phosphide-Based Double Hetero Bipolar Transistor (InP DHBT) (Assignment/Summary)
• Analysis of Mutual-Injection Locking of RTD Patch-Arrays  (Assignment/Summary)
• Contact characterization for indium phosphide based double hetero bipolar transistor (InP DHBT) (Assignment/Summary)
• Investigation in THz RTD Oscillator Array and Concepts (Assignment/Summary)
• Development of a quaternary InGaAsP intermediate layer for use in the collector of InP-DHBTs (Assignment/Summary)

Master's theses

• Wafer-Level Calibration on Indium Phosphide (Assignment/Summary)
• Sensitivity analysis of the Gamma model at varying vehicle parameters in ETCS signal-controlled rail traffic (Assignment/Summary)
• Optimization of active layer in resonant tunnelling diodes (Assignment/Summary)

Master's project works

• Design of high-performance differential THz oscillators in SiGe BiCMOS technology (Assignment/Summary)

 Completed Works 2022

Bachelor theses

• Conceptualization of an on-wafer measurement setup and high-frequency characterization of Indium-Phosphide double-heterostructure bipolar transistors (Assignment/Summary)
• X-Ray Diffractometry Analysis of Epitaxially Grown Semiconductor Layers for Electronic High Frequency Devices (Assignment/Summary)
• Implementation of a transfer-substrate THz measurement setup for characterization of RTD oscillators (Assignment/Summary)
• Modeling of a slot antenna for THz oscillators (Assignment/Summary)
• Process development for the emitter-base diode of an InP HBT (Assignment/Summary)

Master's theses

• Development of epitaxy of 3D GaN nano/microstructures on sapphire (Assignment/Summary)
• Development of an integrated thin-film resistor in the frequency range up to 0.5 THz (Assignment/Summary)
• Design of over 30 GHz Bandwidth Down-Conversion Active Mixer based on InP-HBTs for 6G Applications (Assignment/Summary)
• Design of a Low Noise D-Band Amplifier with more than 20 GHz Bandwidth based on InP-HBTs for 6G Applications (Assignment/Summary)

Completed Works 2021

Bachelor theses

• Optimization of electrical contacts in resonant tunneling diodes (Assignment/Summary)
• Investigation and correction of the proximity effect in the electron-beam lithography process for InP-HBTs (Assignment/Summary)
• Process development for contacting GaN nanowire LED arrays (Assignment/Summary)
• Performance optimization and process development of the resonant tunneling diode for oscillator application (Assignment/Summary)

Bachelor project works

• Concept development of a sub-THz oscillator with patch antennas (Assignment/Summary)

Master's theses

• Design of an InP DHBT and Physical Analysis of Linearity Trade-Offs (Assignment/Summary)
• Abrupt Nanowire pn-Heterojunctions for Detector Applications (Assignment/Summary)