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This paper reports a non-recessed normally off AlGaN/GaN high-electron-mobility transistor (HEMT) with a charge trapping gate dielectric stack. The charge trapping gate dielectric stack featuring a low density of fixed positive charges consists of an O3-based Al2O3 tunneling layer and an O3-based HfO2 blocking layer, both deposited via atomic layer deposition. For HEMT with a 15 nm AlGaN barrier layer, a threshold voltage of 2.57 V and an on-resistance of 8.50 Ω × mm are achieved. For positive bias temperature instability (PBTI) testing, the electric field provided by the 15 nm AlGaN layer serves as a barrier to channel carriers, significantly enhancing the PBTI test stability. The optimized gate dielectric stack enables the fabrication of the non-recessed normally off metal–insulator–semiconductor-HEMT with enhanced threshold voltage (Vth) stability. [ABSTRACT FROM AUTHOR]

This study presents a β-Ga2O3 Schottky barrier diode (SBD) with a Mg current blocking layer (Mg-CBL) fabricated via the Mg-doped spin-on-glass (Mg-SOG) technique, affording a surface roughness damage-free thermal doping process. The proposed technique improves the breakdown voltage (BV) of the β-Ga2O3 SBD from 580 to 2200 V and marginally increases the specific on-resistance from 4.0 to 4.8 mΩ cm2, yielding a notable power figure of merit exceeding 1 GW/cm2. The Mg-CBL effectively captures the electrons and mitigates the electric field, leading to a significant increase in BV and slight decrease in the forward current loss. The temperature-dependent I–V curves reveal that the reverse saturation current decreases owing to the physical mechanism of the Mg-CBL structure. Moreover, the Gaussian distribution model is applied to correct the Schottky barrier inhomogeneity stemming from the Mg-CBL. The results illustrate the promising potential of the Mg-CBL fabricated via the Mg-SOG technique for yielding high-performance β-Ga2O3 SBDs. [ABSTRACT FROM AUTHOR]

We report an experimental investigation on the effect of ground-state charge transfer and its induced electric field on photoexcited charge transfer in van der Waals heterostructures. Two heterostructure samples were fabricated by stacking an undoped WSe2 monolayer with either a Nb-doped or undoped MoSe2 monolayer. While no ground-state charge transfer is expected in the MoSe2/WSe2 heterostructure, the doped holes in the MoSe2:Nb/WSe2 heterostructure can transfer to WSe2, creating a space-charge electric field. By comparing the photoluminescence and time-resolved differential reflectance of the two heterostructures, we find that photoexcited hole transfer from MoSe2 to WSe2 is largely blocked by this field, whereas photoexcited electron transfer from WSe2 to MoSe2 is less affected. These results provide insight into the impact of doping on the charge-transfer performance of van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

In this work, high threshold voltage and breakdown voltage E-mode GaN HEMTs using an Al:HfOx-based charge trapping layer (CTL) are presented. The developed GaN HEMTs exhibit a wide threshold modulation range of ΔVTH ∼ 17.8 V, which enables the achievement of enhancement-mode (E-mode) operation after initialization process owing to the high charge storage capacity of the Al:HfOx layer. The E-mode GaN HEMTs exhibit a high positive VTH of 8.4 V, a high IDS,max of 466 mA/mm, a low RON of 10.49 Ω mm, and a high on/off ratio of ∼109. Moreover, the off-state breakdown voltage reaches up to 1100 V, which is primarily attributed to in situ O3 pretreatment effectively suppressing and blocking leakage current. Furthermore, thanks to the VTH of GaN HEMTs being tunable by initialization voltage using the proposed CTL scheme, we prove that the direct-coupled FET logic-integrated GaN inverters can operate under a variety of conditions (β = 10–40 and VDD = 3–15 V) with commendable output swing and noise margins. These results present a promising approach toward realizing the monolithic integration of GaN devices for power IC applications. [ABSTRACT FROM AUTHOR]

This work adopts interface charge engineering to fabricate normally off metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) on an in situ SiNx/AlGaN/GaN platform using an in situ O3 treatment performed in the atomic layer deposition system. The combination of in situ SiNx passivation and an O3-treated Al2O3/AlGaN gate interface allows the device to provide an excellent breakdown voltage of 1498 V at a low specific on-resistance of 2.02 mΩ cm2. The threshold voltage is increased by 2 V by significantly compensating the net polarization charges by more than five times with O3 treatment as well as reducing the interface traps and improving the high-temperature gate stability. Furthermore, a physical model of fixed charges at the Al2O3/AlGaN interface is established based on dielectric thickness-dependent linear fitting and numerical calculations. The matched device performance and simulated energy band bending elucidate the O3-treated fixed-charge modulation mechanism, providing a practical method for producing normally off GaN MIS-HEMTs. [ABSTRACT FROM AUTHOR]

In this work, we use Si/Tl5Al1/TiN for a source/drain ohmic contact to demonstrate an ultra-low contact resistance of 0.11 Ω mm (ρc = 2.62 × 10−7 Ω cm2) on non-recessed i-InAlN/GaN heterostructures. The Ti5Al1 alloy was used to suppress the out-diffusion of Al and extract N from the InAlN layer, which aided the formation of ohmic contact by improving the tunneling efficiency of electrons, as we have reported in the past work. A thin Si inter-layer combined with the Ti5Al1 alloy is proposed to further reduce contact resistance. A heavy n-type InAlN layer was obtained through doping with Si atoms to improve the tunneling transport of electrons. Furthermore, the TiN inclusions penetrated into the GaN channel because the in-diffused Si promoted the decomposition of GaN at a high annealing temperature and the in-diffused Ti reacted with GaN. These TiN inclusions provided direct contact with two-dimensional electron gas, offering an additional path for the injection of electrons into the channel. The tunneling and spike mechanism worked alternately to lower the contact resistance at different annealing temperatures (dividing at 900 °C), implying that the joint effect of tunneling and the spike mechanism was initially promoted in the formation of ohmic contact. The mechanism of this Si/Ti5Al1/TiN ohmic contact was fully understood through microscopic and thermodynamic analyses. These results shed light on the mechanism for the formation of ohmic contact in a gold-free metal stack for GaN-based HEMTs. [ABSTRACT FROM AUTHOR]