High-reliability passivation of hydrogen-terminated diamond surface by atomic layer deposition of Al2O3

Abstract

Although the two-dimensional hole gas (2DHG) of a hydrogen-terminated diamond surface provides a unique p-type conducting layer for high-performance transistors, the conductivity is highly sensitive to its environment. Therefore, the surface must be passivated to preserve the 2DHG, especially at high temperature. We passivated the surface at high temperature (450 °C) without the loss of C-H surface bonds by atomic layer deposition (ALD) and investigated the thermal reliability of the Al2O3 film. As a result, C-H bonds were preserved, and the hole accumulation effect appeared after the Al2O3 deposition by ALD with H2O as an oxidant. The sheet resistivity and hole density were almost constant between room temperature and 500 °C by the passivation with thick Al2O3 film thicker than 38 nm deposited by ALD at 450 °C. After the annealing at 550 °C in air The sheet resistivity and hole density were preserved. These results indicate the possibility of high-temperature application of the C-H surface diamond device in air. In the case of lower deposition temperatures, the sheet resistivity increased after air annealing, suggesting an insufficient protection capability of these films. Given the result of sheet resistivity after annealing, the increase in the sheet resistivity of these samples was not greatly significant. However, bubble like patterns were observed in the Al2O3 films formed from 200 to 400 °C by air annealing at 550 °C for 1 h. On the other hand, the patterns were no longer observed at 450 °C deposition. Thus, this 450 °C deposition is the sole solution to enabling power device application, which requires high reliability at high temperatures.

Low On-Resistance H-Diamond MOSFETs With 300 °C ALD-Al2O3Gate Dielectric

“…In this work, the 25-nm-thick ALD-grown Al 2 O 3 layer was used as both a gate insulator and a passivation layer. As reported by Daicho et al [16] and Kawarada et al [21], during grown Al 2 O 3 using ALD with water as oxidants, a fresh 2DHG layer produces on the C-H diamond and Al 2 O 3 interface. This conductive layer is protected by the Al 2 O 3 dielectric layer, which lead to the improvement of the stability of the 2DHG.…”

“…Proper dielectrics are useful to improve the device performance [28], [29]. Among them, the Al 2 O 3 dielectric grown at high temperature using atomic layer deposition (ALD) has shown the highest potential for use in H-diamond FETs due to the high breakdown voltage and high stability [14]- [16]. However, the output current is not sufficiently high.…”

High Performance Single Crystalline Diamond Normally-Off Field Effect Transistors

“…The state-of-the-art Hdiamond field effect transistors (FETs) have achieved the cutoff frequency of 53 GHz [3], and the maximum oscillation frequency of 120 GHz [4], and the breakdown voltage over 2 kV [5]. The thermal stability at 400 • C [6] has also been achieved on the devices passivated by Al 2 O 3 .…”

Potential barrier heights at metal on oxygen-terminated diamond interfaces

“…But the chemical stability is not guaranteed at temperatures as high as in other interfaces and reverse current densities turn out not to be lower than 10 −7 A/cm 2 at room temperature, still higher than the thermionic limit. Improvement has been achieved with the help of an oxide layer deposited on the Hterminated surface to build field effect transistors [14,15] but this solution is not relevant for Schottky barrier diodes firstly because it is very difficult to control accurately and in a reproducible way an oxide interlayer made of foreign species with thickness in the subnanometer range. Secondly, the Schottky barrier heights are known to be much smaller than 1 V and even zero for noble metals [16] on the hydrogenated diamond surface, thus inducing far too high reverse currents in rectifiers.…”