Diamond-based diodes for high voltage applications

Abstract: Diamond - the ultimate semiconductor for high power electronics. This statement is justified by diamond's unique material properties: The combination of an ultra-wide bandgap, resulting in a high breakdown field and low leakage current, together with high thermal conductivity and high carrier mobility should theoretically result in the perfect material for manufacturing high voltage, high current electronic devices. The reality, however, looks different: Several research groups have reported premature breakdowns or high leakage currents, influenced by non-optimal device design, poor material quality, or lack of edge termination. Some of these issues have been investigated recently, leading to advances in understanding the detrimental factors. However, especially for high voltage (> 1 kV) devices, there is a crucial need to understand key aspects that limit the performance of diamond devices.

In this work, high voltage diamond vertical Schottky barrier diodes (VSBD) with the capability to block up to 2.6 kV are fabricated and analyzed to gain a better understanding of detrimental factors for diamond electronic devices. A separation of substrate-, epitaxy-, and surface-related effects on device performance indicates that some of the previously unexplained current-voltage characteristics in diamond Schottky diodes can be related to the presence of nitrogen during the epitaxy. To analyze the properties of diodes fabricated on smooth, rough, and polished diamond surfaces, a modified model for forward current-voltage behaviour is applied, showing that a rough surface promotes the formation of a dual Schottky barrier. Additionally, a statistical analysis shows that the advantage of using a high-quality substrate can be masked if the surface preparation is improper - an increase in median field strength accompanied by a decrease in median reverse current density despite the use of an inferior substrate can be explained by the surface finish of the drift layer. As is well known for diamond epitaxy, a substrate with a higher misorientation can be used to obtain smooth as-grown surfaces - this work demonstrates that such Schottky diodes exhibit a poorer performance despite the exceptionally low roughness of these layers. This is attributed to an increased incorporation of scattering centers during growth of the drift layer, which reduce the carrier mobility. On several diamond VSBD in this work, the peculiar effect of a negative temperature coefficient of the reverse current is observed for the first time and explained theoretically.

Although the diodes in the present work exhibit the best unipolar figure of merit for diamond devices above 2 kV, there remains a need for improvement with regard to the missing edge termination and the low substrate quality. To address these issues, the potential of using newly developed buried junction barriers and guard rings is demonstrated. Furthermore, a path to independence from the commercially available substrates of low and varying quality is shown: A well-controllable CVD process yields highly conductive (< 0.1 Ohm cm), freestanding p-doped substrates with low defect density suitable for drift layer epitaxy that exhibit an enhanced crystal quality and carrier mobility. Schottky diodes fabricated on these layers show exceptionally low reverse current densities and achieve the highest unipolar figure of merit in this work.

Combined with the deeper understanding of the factors that negatively impact device performance, these findings support the future development of high-performance diamond electronic devices

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2022

Klassifikation und Themen

• Schlagwort: Diamant ; Galliumnitrid ; Epitaxie ; CVD-Verfahren ; Schottky-Diode ; Siliciumcarbid ; Diamant ; Leistungselektronik ; Halbleiterdiode

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2023
• Urheber: Reinke, Philipp
• Beteiligte Personen und Organisationen: Ambacher, Oliver ; Fiederle, Michael ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/241580
• URN: urn:nbn:de:bsz:25-freidok-2415805
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 15.08.2025, 07:21 MESZ