(NH[sub 4])[sub 2]S[sub x]-Treated AlGaN∕GaN MOS-HEMTs with ZnO Gate Dielectric Layer

Abstract

The function of the ͑NH 4 ͒ 2 S x surface treatment on the AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors ͑MOS-HEMTs͒ was investigated by using the pulsed output characteristics and the low frequency noise measurements. The low carrier concentration and high resistivity 30-nm-thick ZnO film was deposited using the designed vapor cooling condensation system and utilized as the gate dielectric layer of the AlGaN/GaN MOS-HEMTs. The significant improvement of the pulsed output performance and low frequency noise behavior of the ͑NH 4 ͒ 2 S x -treated AlGaN/GaN MOS-HEMTs showed that the ͑NH 4 ͒ 2 S x surface treatment was an effective technique to reduce the surface state density and to obtain high quality interface between the ZnO gate dielectric layer and the AlGaN layer. The decrease of the surface states is attributed to the reduction of Ga dangling bonds and passivation of N vacancies by the formation of Ga-S bond on the AlGaN surface.In recent years, GaN-based semiconductors were successfully utilized in gas sensors, 1,2 electronic devices, 3,4 and optoelectronic devices 5,6 due to the inherent advantages including large and direct energy bandgap, high electron drift velocity, high breakdown field strength, and chemical stabilities. Because the two-dimensional electron gas of the AlGaN/GaN-based heterostrucure reveals high electron mobility, the metal-semiconductor high electron mobility transistors ͑MES-HEMTs͒ for use in high power and high frequency applications were reported previously. 7 However, the performance of the GaN-based MES-HEMTs inevitably suffered from the large gate leakage current and the high surface state density. The surface states on the GaN-based semiconductors surface resulted in the Fermi level pinning effect and the reduction of the Schottky barrier height. 8 To mitigate those drawbacks, passivation method of the high electron mobility transistors structure, which consist of inserting a dielectric layer between the gate metal and the GaN-based semiconductors, was developed. 9,10 Among them, the zinc oxide ͑ZnO͒-based semiconductors are promising candidates of the gate dielectric layer because the ZnO-and the GaN-based semiconductors possess the same wurtzite crystalline structure, nearly identical lattice constant, and bandgap energy. Furthermore, in view of the inherent properties including wide direct band ap ͑3.37 eV͒, large exciton binding energy ͑60 meV͒, and compatibility for wet etching process, ZnO-based semiconductors were used in various electronic and optoelectronic devices. 11-13 Although, several methods were used to deposit ZnO-based semiconductors onto various substrates, 14,15 ZnO usually exhibits n-type conductivity properties owing to the compensation effect of shallow donors induced by oxygen vacancies or zinc interstitials. 16,17 Recently, the vapor cooling condensation system was designed to deposit a high quality intrinsic ZnO ͑i-ZnO͒ film with low carrier concentration ͑7.6 ϫ 10 15 cm −3 ͒ and high resistivity. 18 In this work, the i-ZnO gat...

Improvement of Electron Transport Property and on-Resistance in Normally-OFF Al₂O₃/AlGaN/GaN MOS-HEMTs Using Post-Etch Surface Treatment

“…[11]- [14] The other one is surface pre-passivation of nitride materials with oxidation plasma or alkaline solutions. [15]- [21] The interface issues will become even worse for the gate-recess devices, where a large amount of surface damage and residues (e. g. photoresist, AlClx, and GaClx) may be left after dry etch process. [6] Therefore, interface engineering is much more critical to GaN-based gate-recess MOS-HEMTs.…”