Advanced hydrogen-terminated diamond field effect transistor technology

Qu, Chunlin (2024) Advanced hydrogen-terminated diamond field effect transistor technology. PhD thesis, University of Glasgow.

Abstract

Diamond demonstrates excellent properties for use in high-power and high-frequency electronic devices due to its wide band gap, high carrier mobility, and thermal conductivity. Traditional doping methods prove difficult in diamond due to its strong carbon to carbon bonds and the deep energy levels of most dopants. To overcome these difficulties, transfer doping has emerged as a viable alternative, particularly for hydrogen terminated p-type doped diamond. Hydrogen terminated diamond is widely used for MOSFET fabrication because of its low thermal activation energy.

Given the sensitive nature of hydrogen termination of diamond, this work explores multiple alternative fabrication methods to replace the conventional gold sacrificial layer and protect the hydrogen termination from damage caused by plasma or air exposure during the fabrication process. H-diamond MESFETs with and without ALD Al2O3 encapsulation were fabricated and measured. Device properties such as drain current and gate leakage current were observed to improve after Al2O3 deposition. After the encapsulation, the drain current improved from 16.3 mA/mm to 37.5 mA/mm, while the gate leakage current dropped from 2.49 mA/mm to 0.05 mA/mm. However, high-temperature measurements revealed device degradation at elevated temperatures up to 450K, with the drain current decreasing from 39.6 mA/mm at room temperature to 10 mA/mm at 450K.

Accumulation channel MOSFETs on H-diamond were fabricated using high-temperature annealing and both PVD and ALD Al2O3. With this method, MOSFETs on H-diamond do not rely on transfer doping formed by air adsorbates and hydrogen termination. However, hydrogen termination is still required under the gate to form an accumulation channel. These devices exhibited normally-off properties (Ion/Iof f = 109) and achieved a maximum drain current of 110 mA/mm. The threshold voltage (Vth < −5 V) represents the lowest state-of-the-art value for hydrogen-terminated diamond MOSFETs. The carrier concentration and mobility extracted by the CV analysis is 2×1012 cm−2 and 110 cm2/V ·s, respectively.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Moran, Professor David A.J.
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84831
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 29 Jan 2025 08:12
• Last Modified: 29 Jan 2025 12:17
• Thesis DOI: 10.5525/gla.thesis.84831
• URI: https://theses.gla.ac.uk/id/eprint/84831

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