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Title: Modelling of advanced submicron gate InGaAs/InAlAs pHEMTs and RTD devices for very high frequency applications
Author: Mat Jubadi, Warsuzarina
ISNI:       0000 0004 6497 7224
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2016
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InP-based InAlAs/InGaAs pseudomorphic High Electron Mobility Transistors (pHEMTs) have shown outstanding performance; this makes them prominent in high frequency mm-wave and submillimeter-wave applications. However, conventional InGaAs/InAlAs pHEMTs have major drawbacks, i.e., very low breakdown voltage and high gate leakage current. These disadvantages degrade device performance, especially in Monolithic Microwave Integrated Circuit (MMIC) low noise amplifiers (LNAs). The optimisation of InAlAs/InGaAs epilayer structures through advanced bandgap engineering offers a key solution to the problem. Concurrently, device modelling plays a vital role in the design and analysis of pHEMT devices and circuit performance. In this research, two-dimensional (2D) physical modelling of 1 m and sub-micro metre gate length strained channel InAlAs/InGaAs/InP pHEMTs has been developed, in ATLAS Silvaco. All modelled devices were optimised and validated by experimental devices, which were fabricated at the University of Manchester. An underlying device physics insight is gained, i.e., the effect of changes to the device's physical structure, theoretical concepts and its general operation, and a reliable pHEMT model is obtained. The kink anomalies in the I-V characteristics were reproduced. The 2D simulation results demonstrate an outstanding agreement with measured DC and RF characteristics. The aim of developing linear and non-linear models for sub-micro metre transistors and their implementation in MMIC LNA design is achieved with the 0.25 m In0.7Ga0.3As/In0.52Al0.48As/InP pHEMT. An accurate method for the extraction of empirical models for the fabricated active devices has been developed, and optimised using the Advance Design System (ADS) software. The results demonstrate excellent agreement between experimental and modelled DC and RF data. Precise models for MMIC passive devices are also obtained, and incorporated in the proposed design for a single- and double-stage MMIC LNAs at C- and X-band frequencies. The single-stage LNA is designed to achieve a maximum gain ranging from 9 to 13 dB over the band of operation, while the gain is increased to between 20 dB and 26 dB for the double-stage LNA designs. A noise figure of less than 1.2 dB and 2 dB is expected, for the C- and X-band LNAs respectively, while retaining stability across all frequency bands. Although the RF performance of pHEMT is being vigorously pushed towards the terahertz (THz) region, novel devices such as the Resonant Tunnelling Diode (RTD) are needed to support future ultra-high-speed, high-frequency applications. Hence, the study of physical modelling is extended to quantum modelling of an advanced In0.8Ga0.2As/AlAs RTD device. The aim is to effectively model both large-size and submicron RTDs, using Silvaco's ATLAS software to reproduce the peak current density, peak-to-valley-current ratio (PVCR), and negative differential resistance (NDR) voltage range. The physical modelling for the RTD devices is optimised to achieve an excellent match with the fabricated RTD devices; variations in the spacer thickness, barrier thickness, quantum well thickness and doping concentration are included.
Supervisor: Missous, Mohamed Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: pHEMT ; InGaAs/InAlAs ; physical model ; RTD