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The parameters of open-gate structures treated with different etching time were monitored during the gate recess process, and their impacts on the threshold voltage (Vth) of final fabricated AlGaN/ GaN high electron mobility transistors (HEMTs) based on open-gate structures were discussed in this paper. It is found that Vth can exceed 0V when channel resistance in the recessed region (Ron-open) increases over ~275 Ω mm, maximum current (IDmax) decreases below ~29 mA/mm, or recessed barrier thickness (tRB) is below ~7.5 nm. In addition, tRB obtained by atomic force microscopy measurements and C-V measurements are also compared. Finally, theoretical common criteria based on the experimental results of this work for tRB and Ron-open were established to evaluate the Vth of a regular normally-off AlGaN/GaN HEMTs. The results indicate that these parameters of open-gate structure can be utilized to achieve normally-off HEMTs with controllable Vth. [ABSTRACT FROM AUTHOR]

In this paper, the influence of a drain field plate (FP) on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate—drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD = 10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR. [ABSTRACT FROM AUTHOR]

A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate (FP) techniques to enhance the frequency performance in GaN-based HEMTs. The influences of the field plate on frequency and breakdown performance are investigated simultaneously by using a two-dimensional physics-based simulation. Compared with the conventional T-gate structures with a field plate length of 1.2 μm, this field plate structure can induce the small signal power gain at 10 GHz to increase by 5-9.5 dB, which depends on the distance between source FP and dramatically shortened gate FP. This technique minimizes the parasitic capacitances, especially the gate-to-drain capacitance, showing a substantial potential for millimeter-wave, high power applications. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the trap states in atomic layer deposition Al2O3/InAlN/GaN high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. Trap densities, trap energies and time constants are determined by frequency-dependent conductance measurements. A high trap density of up to 1.6 × 1014 cm−2eV−1 is observed, which may be due to the lack of the cap layer causing the vulnerability to the subsequent high temperature annealing process. [ABSTRACT FROM AUTHOR]

The conventional AlGaN/GaN high electron mobility transistor (HEMT), the AlGaN/GaN/AlGaN HEMT, and the AlxGa1−xN/AlyGa1−yN HEMT are fabricated on sapphire substrates to study the drain-induced barrier-lowering (DIBL) effect. It is found that the AlxGa1−xN/AlyGa1−yN HEMT with AlGaN channel has the lowest DIBL coefficient of 6.7 mV/V compared with the other two HEMTs. This is attributed to the best two-dimensional electron gas confinement of the AlxGa1−xN/AlyGa1−yN structure. This opinion is further confirmed by the conduction band diagrams and electron distribution calculated from the one-dimensional Poisson—Schrödinger equation. [ABSTRACT FROM AUTHOR]

In this paper, we present a 1.8-kV circular AlGaN/GaN/AlGaN double-heterostructure high electron mobility transistor (DH HEMT) with a gate-drain spacing . Compared with the regular DH HEMT, our circular structure has a high average breakdown electric-field strength that increases from 0.42 MV/cm to 0.96 MV/cm. The power figure of merit for the circular HEMT is as high as . The divergence of electric field lines at the gate edge and no edge effect account for the breakdown enhancement capability of the circular structure. Experiments and analysis indicate that the circular structure is an effective method to modulate the electric field. [ABSTRACT FROM AUTHOR]

A novel AlGaN/GaN high electron mobility transistor (HEMT) with double buried p-type layers (DBPLs) in the GaN buffer layer and its mechanism are studied. The DBPL AlGaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8 μm. [ABSTRACT FROM AUTHOR]

The effects of gate length LG on breakdown voltage VBR are investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) with LG = 1 μm∼ 20 μm. With the increase of LG, VBR is first increased, and then saturated at LG = 3 μm. For the HEMT with LG = 1 μm, breakdown voltage VBR is 117 V, and it can be enhanced to 148 V for the HEMT with LG = 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage. A similar suppression of the impact ionization exists in the HEMTs with LG > 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG = 3 μm∼20 μm, and their breakdown voltages are in a range of 140 V–156 V. [ABSTRACT FROM AUTHOR]

We present an AlGaN/GaN high-electron mobility transistor (HEMT) device with both field plate (FP) and low-density drain (LDD). The LDD is realized by the injection of negatively charged fluorine (F–) ions under low power in the space between the gate and the drain electrodes. With a small-size FP and a LDD length equal to only 31% of the gate-drain spacing, the device effectively modifies the electric field distribution and achieves a breakdown voltage enhancement up to two times when compared with a device with only FP. [ABSTRACT FROM AUTHOR]

In this paper, we present a two-dimensional (2D) fully analytical model with consideration of polarization effect for the channel potential and electric field distributions of the gate field-plated high electron mobility transistor (FP-HEMT) on the basis of 2D Poisson's solution. The dependences of the channel potential and electric field distributions on drain bias, polarization charge density, FP structure parameters, AlGaN/GaN material parameters, etc. are investigated. A simple and convenient approach to designing high breakdown voltage FP-HEMTs is also proposed. The validity of this model is demonstrated by comparison with the numerical simulations with Silvaco—Atlas. The method in this paper can be extended to the development of other analytical models for different device structures, such as MIS-HEMTs, multiple-FP HETMs, slant-FP HEMTs, etc. [ABSTRACT FROM AUTHOR]

A non-recessed-gate quasi-E-mode double heterojunction AlGaN/GaN high electron mobility transistor (quasi-E-DHEMT) with a thin barrier, high breakdown voltage and good performance of drain induced barrier lowering (DIBL) was presented. Due to the metal organic chemical vapor deposition (MOCVD) grown 9-nm undoped AlGaN barrier, the effect that the gate metal depleted the two-dimensiomal electron gas (2DEG) was greatly impressed. Therefore, the density of carriers in the channel was nearly zero. Hence, the threshold voltage was above 0 V. Quasi-E-DHEMT with 4.1-μm source-to-drain distance, 2.6-μm gate-to-drain distance, and 0.5-μm gate length showed a drain current of 260 mA/mm. The threshold voltage of this device was 0.165 V when the drain voltage was 10 V and the DIBL was 5.26 mV/V. The quasi-E-DHEMT drain leakage current at a drain voltage of 146 V and a gate voltage of −6 V was below 1 mA/mm. This indicated that the hard breakdown voltage was more than 146 V. [ABSTRACT FROM AUTHOR]