Performance of κ-Ga₂O₃/GaN HEMTs and Normally off Operation by p-GaN Gate

Abstract

The κ-phase gallium oxide (κ-Ga₂O₃) has emerged as a promising material for next-generation electronic devices owing to its ultra-wide band gap, remarkable spontaneous polarization and unique ferroelectricity. We have investigated the two-dimensional electron gas (2DEG) characteristics and device performance of κ-Ga₂O₃/GaN HEMTs via numerical simulations. The κ-Ga₂O₃/GaN heterostructure exhibits a significantly enhanced 2DEG density (~1.05 × 10¹⁴ cm⁻²), which is nearly an order of magnitude higher than that of conventional AlGaN/GaN HEMTs, due to the strong polarization effect. For a barrier thickness of 25 nm, the κ-Ga₂O₃/GaN HEMT exhibits a maximum drain current density (I_D,max) of 4.40 A/mm at V_GS = 2 V and a peak transconductance (g_m,max) of 0.45 S/mm, accompanied by a steep subthreshold swing (SS) of 63.2 mV/decade. Furthermore, we find that the absolute value of threshold voltage increases with the barrier thickness and the peak transconductance decreases with the increase in barrier thickness. When the thickness reaches 40 nm, the 2DEG density becomes saturated with a value of 1.12 × 10¹⁴ cm⁻². Moreover, by incorporating a p-type GaN cap layer into the κ-Ga₂O₃/GaN heterostructure, a normally off operation is achieved, with a positive threshold voltage as the acceptor concentration exceeds 8.0 × 10¹⁷ cm⁻³. These results highlight the potential of κ-Ga₂O₃/GaN heterostructures for high-performance power electronic applications.

1. Introduction

High-electron-mobility transistors (HEMTs) based on GaN are key devices for achieving high-power and high-frequency performance in applications such as power regulation, radar systems, and microwave transmitters [1,2,3]. These devices are highly favored due to their high current density, large power output, and fast switching speed, particularly under high electric field and high-temperature operating conditions. These superior characteristics originate from the polarization-induced two-dimensional electron gas (2DEG), which has a high carrier density (~1 × 10¹³ cm⁻²) and high mobility (~2000 cm² V⁻¹ s⁻¹) at room temperature [4,5]. Further boosting the 2DEG density at the heterointerface is critically essential to enhance the output performance of HEMTs.

Ultra-wide bandgap semiconductor, Ga₂O_3, has emerged as a research hotspot for next-generation power electronics. Notably, κ-Ga₂O₃, owing to its non-centrosymmetric orthorhombic crystal structure, exhibits a high spontaneous polarization. The theoretical spontaneous polarization coefficient reaches up to 23 μC/cm², exceeding those of III-nitride semiconductors such as AlN (−8.1 μC/cm²) and GaN (−2.9 μC/cm²) [6,7]. Heterostructures based on κ-Ga₂O₃ can support extremely high-density 2DEG [8,9,10]. In addition, κ-Ga₂O₃ possesses a high dielectric constant [7] and unique ferroelectric properties [6,8]. These features introduce an additional degree of freedom for realizing the high density of 2DEG [11,12]. The growth of κ-Ga₂O₃ on GaN and other III-nitride semiconductors has been demonstrated to be feasible [13,14,15,16,17,18]. Facilitated by high elastic strain, high-quality κ-Ga₂O₃ thin films can be achieved on lattice-mismatched substrates such as sapphire, GaN, AlN, and SiC using techniques including halide vapor phase epitaxy (HVPE), mist chemical vapor deposition (mist-CVD), and metal–organic chemical vapor deposition (MOCVD) [13,19,20,21,22,23,24,25,26]. These suggest the potential for the design and fabrication of high-performance HEMT devices based on κ-Ga₂O₃ and GaN heterostructures.

Hybrid density functional theory predicted that the κ-Ga₂O₃/GaN heterostructure exhibits an ultra-high-density 2DEG with a sheet concentration exceeding 10¹⁴ cm⁻² without intentional doping [6,27,28]. Although theoretical studies predict an ultrahigh 2DEG density in κ-Ga₂O₃/GaN heterostructures, experimentally reported carrier concentrations are usually lower than the ideal values. This discrepancy may originate from trap states within the barrier layer and interface nonidealities, including oxygen vacancies, impurity-related traps, interface roughness, and surface/interface states. These defects can trap electrons, screen the polarization field, reduce the effective interfacial charge density, and degrade carrier mobility [13,25]. Therefore, it is important to distinguish the intrinsic polarization-induced charge-control mechanism from extrinsic defect-related limitations. In this work, we propose a ferroelectric/polar HEMT based on a κ-Ga₂O₃/GaN heterostructure. Numerical simulations are carried out to clarify the ideal electrostatic behavior of κ-Ga₂O₃/GaN HEMTs and to examine how the κ-Ga₂O₃ barrier thickness and p-GaN cap layer modulate the 2DEG density, threshold voltage, and device performance.

The results reveal that the κ-Ga₂O₃/GaN heterostructure exhibits a significantly enhanced 2DEG density (~1.05 × 10¹⁴ cm⁻²), leading to markedly improved current density, transconductance, and reduced on-resistance compared with conventional AlGaN/GaN devices. For a barrier thickness of 25 nm, the κ-Ga₂O₃/GaN HEMT exhibits a maximum drain current density (I_D,max) of 4.40 A/mm and a peak transconductance (g_m,max) of 0.45 S/mm, accompanied by a steep subthreshold swing (SS) of 63.2 mV/decade. The barrier thickness is found to effectively modulate the 2DEG density and threshold voltage. The absolute value of Vth increases with the barrier thickness, and the peak transconductance decreases with the increase in barrier thickness. Furthermore, the introduction of a p-GaN cap layer enables normally off operation through depletion of the 2DEG, dependent on acceptor concentration. The threshold voltage is positive as the acceptor concentration exceeds 8.0 × 10¹⁷ cm⁻³.

2. Model and Methods

The κ-Ga₂O₃/GaN HEMT consists of a 25 nm-thick κ-Ga₂O₃ barrier layer and a 1.5 μm-thick GaN channel layer, as shown in Figure 1a. An Al_0.3Ga_0.7N/GaN HEMT is also investigated for comparison (Figure 1b). The width of both HEMTs is 100 μm. The gate length (L_G), gate-source distance (L_GS) and gate-drain distance (L_DS) were set to 2 μm, 3 μm and 3 μm, respectively. The source and drain electrodes were defined as Ohmic contacts, while the gate electrode was defined as a Schottky contact with a work function of 5.0 eV [29]. In the present simulations, the gate was modeled as an ideal Schottky contact with a fixed work function, enabling us to clarify the intrinsic electrostatic modulation induced by the κ-Ga₂O₃/GaN polarization discontinuity and the barrier thickness. However, in realistic devices, the effective gate barrier height and threshold voltage can be affected by the detailed band alignment at the metal/κ-Ga₂O₃ or dielectric/κ-Ga₂O₃ interface, as well as by interfacial dipoles and trap states. Therefore, the calculated threshold-voltage values should be interpreted as idealized trends. Experimental techniques such as angle-resolved XPS, UPS, and C-V characterization are required to determine the actual band offsets and validate the simulated gate-control behavior [30]. We assume that κ-Ga₂O₃/Al_0.3Ga_0.7N was grown along the [001] direction upon the polar plane (0001) of Ga-faced GaN with spontaneous polarization opposite to the z-axis. Considering the difference in crystalline structure and large lattice mismatch, the κ-Ga₂O₃ film was considered fully relaxed, eliminating piezoelectric polarization (P_PE), and only spontaneous polarization (P_SP) was considered [21,26].

Figure 1. Cross-section structure of (a) κ-Ga₂O₃/GaN and (b) AlGaN/GaN HEMTs.

The electrical characteristics of the two HEMTs were calculated using the TCAD device simulator Silvaco Atlas (version 5.0.10.R). The models included a parallel electric field model for velocity saturation, Shockley-Read-Hall, an incomplete ionization model and polarization model. All calculations were based on the Fermi-Dirac statistics [29,31]. The density of states of conduction band for κ-Ga₂O₃ was estimated to be 2.95 × 10¹⁸ cm⁻³, based on an effective electron mass (m_n*) of 0.24 m₀ [32]. The dielectric constant (${\epsilon }_r$) of 32 was used for κ-Ga₂O₃ [7]. The material parameters, including bandgap energy (E_g), conduction band offset between the barrier layer and GaN (ΔEc), electron effective mass relative to free electron mass (m_n*/m₀), ε_r, and P_SP, for κ-Ga₂O₃, Al₀.₃Ga₀.₇N and GaN are listed in Table 1 [7,32,33,34]. An Al mole fraction of 0.30 was selected for the reference AlGaN/GaN HEMT because Al_0.3Ga_0.7N is commonly used in conventional GaN-based HEMTs to achieve a relatively high polarization-induced 2DEG density while avoiding excessive lattice mismatch and material degradation [35]. Thus, Al_0.3Ga_0.7N/GaN serves as a representative benchmark for evaluating the potential advantage of the κ-Ga₂O₃/GaN heterostructure. The κ-Ga₂O₃ barrier and GaN channel were treated as unintentionally doped, and the 2DEG was mainly induced by polarization discontinuity rather than intentional donor doping. For the p-GaN-gated structure, the acceptor concentration in the p-GaN cap layer was varied from 1 × 10¹⁷ to 1 × 10¹⁸ cm⁻³ to study the threshold-voltage shift.

Table 1. Key material parameters for GaN, κ-Ga₂O₃ and AlN in simulations.

Materials	Eg (eV)	ΔEc (eV)	mn*/m0	${\mathit{\epsilon }}_{\mathit{r}}$	PSP (μC/cm2)
GaN	3.4	0	0.20	8.9	−2.9
κ-Ga2O3	5.0	1.38	0.24	32	23
AlN	6.1	1.9	0.33	8.5	−8.1

3. Results and Discussion

3.1. Comparison of κ-Ga₂O₃/GaN and AlGaN/GaN

Figure 2a presents the calculated band structure and electron density distribution of the κ-Ga₂O₃/GaN heterojunction. The conduction band (E_C) and valence band (E_V) exhibit a pronounced linear bending across the κ-Ga₂O₃ barrier layer, which originates from the strong polarization fields in κ-Ga₂O₃/GaN heterostructure. At the κ-Ga₂O₃/GaN heterointerface, a conduction band offset of 1.38 eV is formed [34], creating a triangular potential well on the GaN side that serves to confine charge carriers. The electron concentration shows a distinct, sharp peak localized at the interface, confirming the formation of a 2DEG. The peak volume concentration reaches 9.90 × 10²⁰ cm⁻³, corresponding to a sheet electron density (n_s) of 1.05 × 10¹⁴ cm⁻². For comparison, the band structure and electron density distribution of the conventional AlGaN/GaN heterojunction are calculated (Figure 2b). A confined 2DEG is also formed due to the polarization discontinuity at the Al₀.₃Ga₀.₇N/GaN interface. The peak density of the 2DEG is about 8.21 × 10¹⁹ cm⁻³, corresponding to a sheet concentration ns of 1.09 × 10¹³ cm⁻², which is in line with the experimental observations [36]. Compared with the κ-Ga₂O₃/GaN heterojunction, the Al₀.₃Ga₀.₇N/GaN system exhibits a weaker polarization-induced electric field, a shallower potential well, and a significantly lower 2DEG sheet density. The κ-Ga₂O₃/GaN heterojunction achieves a 2DEG sheet density one order of magnitude higher than that of Al₀.₃Ga₀.₇N/GaN, exceeding the reported upper limit of 6 × 10¹³ cm⁻² for AlN/GaN heterojunctions [37,38]. This superior performance originates from the stronger polarization-induced electric field and deeper potential well in κ-Ga₂O₃/GaN, demonstrating its excellent carrier confinement capability for high-power electronic devices.

Figure 2. Energy band and electron density distribution for (a) κ-Ga₂O₃/GaN and (b) AlGaN/GaN heterostructures with the barrier thickness of 25 nm. n_s is the sheet concentration obtained by integrating n.

Figure 3 shows the transfer characteristics at the drain-source voltage V_DS = 5 V. Drain current density, I_DS, and transconductance as a function of gate-source voltage, V_GS, are plotted. As illustrated, the maximum drain current density (I_D,max) for the κ-Ga₂O₃/GaN and the AlGaN/GaN reaches 4.40 and 0.49 A/mm at V_GS = 2 V, respectively. The I_D,max of κ-Ga₂O₃/GaN is approximately one order of magnitude higher than that of AlGaN/GaN due to the higher 2DEG density at the κ-Ga₂O₃/GaN interface [39]. Additionally, the g_m,max of κ-Ga₂O₃/GaN HEMT (0.45 S/mm) is about 5 times higher than that of AlGaN/GaN HEMT (0.09 S/mm). Further, as shown in the inset of Figure 3, the I_ON/I_OFF ratio is about 10¹³ for the AlGaN/GaN and 10¹² for the κ-Ga₂O₃/GaN with L_G = 2 μm. A distinct discrepancy in reverse leakage current is observed between the two HEMT structures. The different off-state current levels of the two HEMTs are closely related to their different polarization-induced electrostatics. Because the κ-Ga₂O₃/GaN heterostructure possesses a much higher 2DEG density, the channel is more difficult to fully deplete under the same negative gate bias, resulting in a higher residual subthreshold current. Since detailed trap-assisted leakage mechanisms were not explicitly included in the present simulation, the leakage characteristics should be understood as idealized trends associated with polarization-induced charge control.

Figure 3. I_DSV_GS and g_mV_GS for the κ-Ga₂O₃/GaN and AlGaN/GaN HEMTs at V_DS = 5 V. The inset is the transfer characteristics in logarithmic scale for the κ-Ga₂O₃/GaN and the reference AlGaN/GaN HEMTs.

Based on the data, we extracted the threshold voltage (Vth) for both HEMTs via a constant-current method. Vth is defined as the gate voltage when I_DS reaches 10 μA/mm in the subthreshold region [40,41]. The Vth values for the κ-Ga₂O₃/GaN and AlGaN/GaN are −16.8 V and −6.2 V, respectively. The κ-Ga₂O₃/GaN HEMT has a more negative Vth compared with the AlGaN/GaN HEMT. This behavior can be attributed to the higher 2DEG density at the κ-Ga₂O₃/GaN interface. Additionally, we calculated the subthreshold swing (SS). The SS values are 84.0 mV/decade for AlGaN/GaN HEMT, and 63.2 mV/decade, approaching the near-ideal range, for the κ-Ga₂O₃/GaN HEMT [42]. This implies that the polarization-induced higher-density 2DEG at the κ-Ga₂O₃/GaN interface enables the device to achieve a high-power density and a low power consumption [43].

The output characteristics are presented in Figure 4. For the κ-Ga₂O₃/GaN HEMT, the maximum drain current density is 10.87 A/mm at V_DS = 15 V, V_GS = 2 V. For the AlGaN/GaN, the maximum drain current density is only 0.78 A/mm. The on-resistance (R_ON), extracted from the linear region of the case of V_GS = 2 V, is 0.89 Ω·mm for the κ-Ga₂O₃/GaN and 10.21 Ω·mm for the AlGaN/GaN. It means that κ-Ga₂O₃/GaN has a lower conduction loss in comparison with AlGaN/GaN. The findings confirm that κ-Ga₂O₃/GaN is a promising candidate to address the challenges of high-power applications.

Figure 4. I_DSV_DS for (a) the κ-Ga₂O₃/GaN and (b) AlGaN/GaN.

The very high 2DEG density predicted for κ-Ga₂O₃/GaN heterostructures is beneficial for high current drivability. Meanwhile, carrier mobility constitutes another key factor determining the practical performance of κ-Ga₂O₃/GaN HEMTs. The actual channel mobility and dynamic device performance may be limited by dislocations, native surface traps on κ-Ga₂O₃ barrier layer, and κ-Ga₂O₃/GaN interface roughness and traps. These nonidealities can introduce Coulomb scattering, trap-assisted leakage, and current collapse [44,45]. Therefore, high-quality epitaxial growth and interface engineering are expected to be critical for realizing the full potential of κ-Ga₂O₃/GaN HEMTs. High-k passivation layers and nanolaminate dielectrics grown by ALD or PEALD, such as HfO₂/La₂O₃-based stacks used in AlGaN/GaN systems, may provide possible routes to suppress surface states and improve carrier transport [46]. For κ-Ga₂O₃/GaN devices, further studies are needed to evaluate the dielectric/κ-Ga₂O₃ band alignment, threading dislocations and native surface states within the κ-Ga₂O₃ epitaxial layer, as well as trap density at the κ-Ga₂O₃/GaN heterointerface to optimize overall electrical performance.

3.2. Effect of Barrier Thickness

Now, we investigate the influence of κ-Ga₂O₃ thickness on the conduction band and 2DEG concentration for the κ-Ga₂O₃/GaN HEMT. As shown in Figure 5a, the Fermi level penetrates into the conduction band, leading to the formation of a triangular quantum well for all the thicknesses we studied. This causes the generation of 2DEG due to polarization-induced electron transfer from donor-like surface states on the top surface of the barrier layer to the GaN conduction band at the interface. The 2DEG density increases with κ-Ga₂O₃ thickness and gradually approaches saturation with a value of 1.12 × 10¹⁴ cm⁻² when the thickness is around 40 nm within the investigated range (Figure 5b). This behavior originates from the electrostatic balance between the polarization field and the screening field generated by the transferred electrons. A thicker κ-Ga₂O₃ barrier produces a larger potential drop and promotes electron transfer to the interface, while the accumulated 2DEG screens the polarization field and limits further increase in sheet density. Therefore, in the ideal model, the 2DEG density is expected to saturate rather than increase indefinitely [47,48]. In practical devices, however, an excessively thick κ-Ga₂O₃ layer may introduce defects, roughness, strain relaxation, and trap states, which can reduce the effective carrier density and mobility. Thus, the optimized barrier thickness should consider both the saturated 2DEG density and the carrier mobility degradation caused by trap states, defects and interface quality issues.

Figure 5. (a) Conduction band profiles and (b) 2DEG sheet concentrations of the κ-Ga₂O₃/GaN heterostructure with varying κ-Ga₂O₃ thickness.

Vth and g_m,max, as a function of κ-Ga₂O₃ thickness, are plotted in Figure 6. The transfer characteristics are also given. The value of Vth is negative (Figure 6a), and its absolute value increases with the barrier thickness due to the deepening of the quantum well. It indicates that one can achieve the desired Vth by tuning the thickness of the κ-Ga₂O₃ barrier. In addition, the maximum drain current also increases with κ-Ga₂O₃ thickness due to the enhanced electron density in the channel.

Figure 6. Vth (a) and g_m,max (b) as a function of κ-Ga₂O₃ thickness for the κ-Ga₂O₃/GaN HEMTs. The insets are g_mV_GS and I_DSV_GS with various thicknesses of κ-Ga₂O₃, respectively.

The peak transconductance (Figure 6b) decreases with the increase in barrier thickness, owing to the strong impact of the lowering gate capacitance for thicker barriers [48]. It implies that the HEMT suffers from loss of gate control with the increase in κ-Ga₂O₃ thickness. After careful analysis, we observed that he g_m,max reaches 1.08 S/mm when the barrier layer is 2 nm. For this thin barrier, the maximum drain current is close to 2.0 A/mm (see the insets of Figure 6). The value is still much larger than that of conventional AlGaN/GaN HEMT. It can be concluded that the κ-Ga₂O₃/GaN heterostructure is suitable for fabricating ultra-thin devices, which maintains a large drain current and a high transconductance.

3.3. Effect of p-GaN Gate

The above κ-Ga₂O₃/GaN HEMTs display a normally on operation due to the presence of a 2DEG channel at zero gate bias. However, normally off enhancement mode devices with positive threshold voltages are more desirable in power electronic applications, especially in the design of fail-safe power switches and RF power amplifiers [48,49]. To realize the normally off operation, a p-GaN gate layer was introduced at the top of the channel layer, as shown in Figure 7a. The thicknesses of the κ-Ga₂O₃ barrier and p-GaN cap layer were set to be 3 nm and 50 nm, respectively.

Figure 7. (a) Schematic structure of the p-GaN gated κ-Ga₂O₃/GaN HEMT. (b) Transfer characteristics and (c) Ec at V_GS = V_DS = 0 V for the κ-Ga₂O₃/GaN HEMTs with and without p-GaN layer. Na denotes the acceptor concentration in the p-GaN layer, and E_F represents the Fermi level. The magnified view of the circled region in (c) is displayed in (d).

From the transfer characteristics of HEMTs (shown in Figure 7b), we found that the κ-Ga₂O₃/GaN HEMT without a cap layer exhibits a threshold voltage of −1.50 V at V_DS = 5 V and a maximum drain current density of 2.26 A/mm at V_GS = 2 V. For the p-GaN capped devices, Vth shifts positively as the acceptor concentration in the p-GaN layer increases above 8 × 10¹⁷ cm⁻³, implying the realization of enhancement-mode operation. To understand the reason for the positive shift in Vth, we plot the Ec diagrams in Figure 7c. For the heterostructure without the p-GaN layer, the conduction band edge lies below the Fermi level near the interface. The p-type conductivity of the GaN cap layer effectively lifts up the potential, depletes the 2DEG and consequently results in the positive shift in Vth [50]. It should be noted that the incorporation of a p-GaN cap layer does not guarantee normally off operation. An appropriate choice of the acceptor concentration of p-GaN is crucial for efficiently depleting the 2DEG and realizing a normally off operation.

It should be noted that a κ-Ga₂O₃ thickness of 3 nm is adopted for the p-GaN-gated structure. This ultrathin barrier yields a reduced 2DEG density and a less negative threshold voltage, which enables full depletion of the channel via the p-GaN cap layer. For a thicker κ-Ga₂O₃ barrier, such as 25 nm, the much higher polarization-induced 2DEG density would make the threshold voltage more negative, and the same p-GaN cap may become insufficient to realize normally off operation. In that case, stronger depletion would be required through a higher acceptor concentration, a thicker p-GaN cap, gate recess engineering, high-work-function gate metals, or dielectric/interface charge engineering. Therefore, the design of p-GaN-gated κ-Ga₂O₃/GaN HEMTs involves a trade-off between high current density and normally off operation [51].

Although the p-GaN cap layer can deplete the 2DEG and shift the threshold voltage positively, the threshold voltage of a practical p-GaN-gated κ-Ga₂O₃/GaN HEMT may also be affected by surface and interfacial layers [52]. Native oxide vacancies, residual interlayers, fixed charges, interface dipoles, and trap states at the metal/p-GaN, p-GaN/κ-Ga₂O₃, or κ-Ga₂O₃/GaN interfaces can modify the local band bending and further alter the equilibrium 2DEG sheet density as well as threshold voltage. Therefore, surface passivation processes and careful interface control are required for reproducible normally off operation.

Because experimental demonstrations of complete κ-Ga₂O₃/GaN HEMTs, especially p-GaN-gated normally off devices, remain limited, the present simulation results should be regarded as predictive design guidelines rather than fully benchmarked device datasets, highlighting the necessity of further experimental verification. Hall measurements can be used to determine the 2DEG density and mobility; C–V measurements can evaluate charge control and threshold behavior; and XPS/UPS or angle-resolved XPS can determine the band offsets and band bending at the gate and p-GaN/κ-Ga₂O₃ interfaces. Such systematic experimental characterizations would enable comprehensive verification of device performance and establish a direct quantitative correlation among interfacial band alignment, p-GaN-mediated channel depletion, and threshold voltage shift.

4. Conclusions

In summary, we have systematically investigated the 2DEG characteristics and performance of κ-Ga₂O₃/GaN HEMTs through numerical simulations, in comparison with conventional AlGaN/GaN devices. Owing to the strong polarization effect of κ-Ga₂O₃, the κ-Ga₂O₃/GaN heterostructure yields an ultrahigh interfacial 2DEG sheet concentration of ~1.05 × 10¹⁴ cm⁻², nearly one order of magnitude higher than that of conventional AlGaN/GaN heterostructures. The enhanced 2DEG density enables a maximum drain current density of 4.40 A/mm, a peak transconductance of 0.45 S/mm, and a markedly reduced on-resistance of 0.89 Ω·mm in the κ-Ga₂O₃/GaN HEMT at the barrier thickness of 25 nm and V_GS = 2 V. Furthermore, the influence of barrier thickness on the electronic properties has been clarified. The absolute value of Vth increases with the barrier thickness, and the peak transconductance decreases with the increase in barrier thickness. The interfacial 2DEG density exhibits saturation behavior at a barrier thickness of 40 nm, with a saturated value of 1.12 × 10¹⁴ cm⁻². This tunability enables flexible control of threshold voltage and output performance.

Moreover, by integrating a 50 nm-thick p-GaN cap layer with an acceptor concentration exceeding 8.0 × 10¹⁷ cm⁻³ into the 3 nm-thick κ-Ga₂O₃ barrier-based GaN HEMT, the interfacial 2DEG can be effectively depleted, enabling the successful realization of normally off operation with a positive threshold voltage of 0.92 V. Our findings reveal the significant advantages of κ-Ga₂O₃/GaN heterostructures for high-performance and normally off power electronics, and provide important physical insights and design guidelines for next-generation polarization-engineered devices.