AlGaN/GaN heterostructures with an AlGaN layer grown directly on reactive-ion-etched GaN showing a high electron mobility (>1300 cm²V⁻¹s⁻¹)

Abstract

In this study, the metal–organic-vapor-phase-epitaxial growth behavior and electrical properties of AlGaN/GaN structures prepared by the growth of an AlGaN layer on a reactive-ion-etched (RIE) GaN surface without regrown GaN layers were investigated. The annealing of RIE-GaN surfaces in NH3 + H2 atmosphere, employed immediately before AlGaN growth, was a key process in obtaining a clean GaN surface for AlGaN growth, that is, in obtaining an electron mobility as high as 1350 cm2 V−1 s−1 in a fabricated AlGaN/RIE-GaN structure. High-electron-mobility transistors (HEMTs) were successfully fabricated with AlGaN/RIE-GaN wafers. With decreasing density of dotlike defects observed on the surfaces of AlGaN/RIE-GaN wafers, both two-dimensional electron gas properties of AlGaN/RIE-GaN structures and DC characteristics of HEMTs were markedly improved. Since dotlike defect density was markedly dependent on RIE lot, rather than on growth lot, surface contaminations of GaN during RIE were believed to be responsible for the formation of dotlike defects and, therefore, for the inferior electrical properties.

Control of V th of the enhancement high-frequency AlGaN/GaN HEMT fabricated by oxygen-based digital etching

“…Moreover, two-dimensional electron gas (2DEG) with high sheet charge densities above 1.0 × 10 13 cm −2 can be formed at AlGaN/GaN heterostructure owing to the strong polarization difference and high conduction band offset at the interface to provide the required high current for the HEMT. [1][2][3][4][5][6][7][8][9] Gate recessed etching is a promising technique to adjust threshold voltage for GaN HEMT. [10][11][12] It is also one of the major techniques to fabricate an enhancement mode (normallyoff) GaN HEMT device.…”

Advancements in energy efficientGaNpower devices and power modules for electric vehicle applications: a review

“…38 The growth of AlGaN/GaN heterostructure with lattice matched AlIn(Ga)N back barrier is proposed for the GaN HEMTs. 39 The growth process is fulfilled at a pressure and temperature of 400 Torr and 900 C. It is superior with good 2DEG properties along with a low off-current of~2 × 10 −7 A/mm as compared to the traditional AlGaN and InGaN back barrier. Another research work is reported based on the AlGaN/RIE (reactive-ion-etched) GaN wafers as highlighted in Figure 4C.…”

Evidence of reduced interface states in Al2O3/AlGaN MIS structures via insertion of ex situ regrown AlGaN layer

“…20) Almost all conceivable approaches have been undertaken with various levels of success. 21) Meanwhile, combining the well-established recessed-gate technology and a recent ex situ regrowth technology developed by Yamamoto et al, [22][23][24] we have reported Al 2 O 3 /AlGaN/GaN MIS-HEMTs exhibiting a record combination of maximum drain current and V th . 25) While the effects of recess structure on the performance of GaN-based HEMTs have been relatively well understood, 26) there have been no reports on the impact of ex situ AlGaN regrowth on the resulting of insulator/AlGaN interfacial properties.…”

“…For the ex situ regrowth of a 3 nm thick Al 0.25 Ga 0.75 N layer using MOVPE, we adopted the method previously developed by our group. [22][23][24] To form ohmic contacts, a metal stack of Ti/Al/ Mo/Au was deposited by electron beam evaporation, immediately followed by rapid thermal annealing at 880 °C for 30 s under N 2 ambient. As a gate insulator, a 24 nm thick Al 2 O 3 insulator layer was then deposited by atomic layer deposition using trimethylaluminum and ozone as aluminum and oxygen sources, respectively.…”

“…Before the actual ex situ regrowth, the sample was first annealed inside the MOVPE chamber in NH 3 and H 2 atmosphere at 850 °C. 23) This annealing process in NH 3 and H 2 atmosphere could have led to slight etching of the original AlGaN surface by hydrogen, 22) removing the disorder of dangling bonds and contributing to the formation of excellent surface. Furthermore, the formation fresh surface after the 3 nm thick AlGaN regrowth, could have further reduced degree of disorder of dangling bonds in RAS devices, and therefore, could have reduced D it as compared to reference devices.…”