• Khairul Nabilah Zainul Ariffin

Student thesis: Phd


It has been over a half-century since Leo Esaki in the early 1960 reported the first tunnel diodes. These first quantum electron tunnelling devices were named Esaki diode in his honour. This was a testament to quantum transport in a semiconductor which was subsequently demonstrated to be extremely stable. The work reported in this thesis probed into the functionality of three new and different types of tunnel diodes, namely a Single Barrier Asymmetric Spacer Tunnel (ASPAT), a Double Quantum Well Asymmetric Spacer Tunnel (QASPAT), and a Double Barrier Quantum Well Resonant Tunnelling Diode (RTD), with the aim to investigate the capabilities of each tunnel device. Adorned with the status of a maturing tunnel diode within the semiconductor arena, the ASPAT diode appears to be an exceptionally promising candidate for high-frequency applications, due to its highest theoretical cut-off frequency which can reach up to 2 THz. Its asymmetric spacer structure leads to a unique asymmetrical I-V characteristic that offers significant improvement over Schottky and Planar Doped Barrier (PDB) diodes without sacrificing sensitivity or dynamic range aspects. Such stimulating feature is indeed paramount for implementations of high-speed detectors, especially for operations in the mm-wave/THz regime. In this research, an original and novel idea to tweak the ASPAT structure has led to a most remarkable feature that reflects a dual-function device in a single diode. Originating from the ASPAT structure, the I-V characteristic has zero-bias turn-on feature but showed a most interesting feature of negative differential resistance (NDR) region in reverse bias enabling this device to function as both a detector and an oscillator, depending on bias voltage. This device is temperature independent as its I-V characteristics does exhibit insensitivity to temperature over a wide range of temperature variations. It displays less than ~ 5 % current change when compared to the I-V characteristics at selected temperatures (from 77 K to 400 K), to the I-V at room temperature. Quantum based devices, particularly RTD, appears to be promising devices that possess the capability of providing close to ~ 1 mW of RF power in the millimetre wave and THz regions of the electromagnetic spectrum. This feature is mainly attributed to their unique NDR feature showcased in the I-V characteristic of the RTDs reported here. Following modelling and validation of ASPAT and QASPAT diodes with high indium-rich material profiles, the study was then extended to quantum modelling of advanced double barrier In0.8Ga0.2As/AlAs RTD. The work culminated in an accurate physical model which was exploited to minimise fabrication costs in developing experimental devices. The two-dimensional (2D) simulation for all devices under study demonstrated outstanding agreement with the measured DC and RF characteristics validating the models used.
Date of Award1 Aug 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMohamed Missous (Supervisor) & Robin Sloan (Supervisor)


  • RTD
  • Tunnel Diode
  • InGaAs/AlAs
  • GaAs/AlAs

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