(M.Sc./B.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: M.Sc. Patrick Häuser

(M.Sc.) Optimization of Emitter and Base Contacts for Nano-Scaled HBTs

Background:

The indium phosphide double heterojunction bipolar transistor (InP DHBT) is a promising candidate for high-frequency applications. For high-performance HBTs, low-resistance metal-semiconductor contacts are necessary.

Task:

In the context of this work, the parameters of the evaporation process for n- and p-contacts will be developed. Various pre-treatment methods for the wafer will be investigated for the development of nano-scaled contacts. Different apparatus and measurement techniques will be used for the characterization of the wafer and the contacts, such as SEM, AFM, TLM measurements, and Hall measurements.

Supervisor: M.Sc. Hao Zhang

(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.) Development of an RTD Terahertz Receiver

In the frequency range around 1 terahertz (THz), many new applications are currently being developed, such as contactless sensor arrays for simultaneous material detection and object localization. The interface between the sensor array and conventional silicon-based electronics is formed by frequency converters, which convert the THz signals into the single-digit GHz range for further processing. Commercially available systems are based on actively cooled split-block integrated mixer/amplifier/multiplier chains (Mix-AMC) and exhibit high mixer losses and power dissipation. The use of novel circuit concepts based on resonant tunneling diodes (RTD) promises to improve mixer loss, power dissipation, and integration density by orders of magnitude. However, circuit design for RTDs is non-trivial and unconventional.

The goal of this work is to develop robust circuit concepts and a physical layout for an RTD receiver, as well as to investigate the theory of nonlinear frequency conversion in RTD circuits through symbolic harmonic-balance calculations. The field has detailed preliminary work on the technological realization of corresponding circuits, the epitaxial growth of RTD layer stacks, and the design and simulation of various RTD oscillator circuits and arrays, allowing the receiver to be designed from a toolbox of high-frequency components (MIM capacitors, vias, patch antennas, etc.).

Supervisor: M.Sc. Jonas Watermann

(M.Sc.) Atomistic Simulations of Quaternary Semiconductor Compounds

The double heterojunction bipolar transistor (DHBT) exhibits impressive high-frequency characteristics and is a candidate for broadband communication applications. However, for data transmission, not only the cutoff frequency but also the linearity of the transistor is crucial. A quaternary material grading in the collector of the transistor is essential for linearity. By clever band engineering, energetic barriers in the conduction band can be avoided, and nonlinear current sources such as direct band-to-band tunneling or trap-state-assisted tunneling can be minimized.

Since experimental data on the band structure and particularly the electron affinity are lacking for most quaternary material combinations, the goal of this master’s thesis is to support our MOVPE epitaxy development with atomistic simulations using the commercial software "QuantumATK" and "Sentaurus TCAD." Target parameters include band structure and electron affinity, as well as transport simulations based on the non-equilibrium Green's function (NEGF) formalism and hydrodynamic electron transport. The theoretical results will also be experimentally verified through epitaxial test structures.

Supervisor: M.Sc. Jonas Watermann

(M.Sc.) Design and Fabrication of Metasensors

A metasensor is formed from a periodic meta-surface whose resonance frequency changes depending on its dielectric environment, for example, through strong coupling to resonances of organic molecules or nanoparticles. By measuring this frequency shift, the meta-surface can be used as a sensor. The frequency shift is usually determined through complex laser-based terahertz spectroscopy. Therefore, the goal of this work is to couple the metasensor to an electronic oscillator based on a resonant tunneling diode (RTD) to transfer the frequency shift to the RTD. The main task of the work is to design and fabricate suitable meta-surfaces through metal evaporation on silicon wafers. Subsequently, the coupling to our already characterized RTD oscillators will be verified in a free-space setup.

Supervisor: M.Sc. Jonas Watermann

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

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)